Akbari, H., Taha, H. 1992. The Impact of Trees and White Surfaces on Residential Heating and Cooling Energy Use in Four Canadian Cities. Energy, 17(2), 141-149.
Abstract: We have investigated the potential of using vegetation and high-albedo materials in Toronto, Edmonton, Montreal, and Vancouver, Canada, to modify the urban microclimate, thereby saving residential heating and cooling energy use. Parametric computer simulations of microclimates and energy performance of prototypical houses were our primary analysis tools. The building prototypes included a detached one-story and a detached two-story single family house, as well as a row house. The simulations indicated that by increasing the vegetative cover of the neighborhood by 30% (corresponding to about three trees per house) and increasing the albedo of the houses by 20% (from moderate-dark to medium-light color), the heating energy in Toronto can be reduced by about 10% in urban houses and 20% in rural houses, whereas cooling energy can be reduced by 40 and 30%, respectively. The annual savings in heating and cooling costs for different houses ranged from $30 to $180 in urban areas and from $60 to $400 in rural zones. In urban houses of Edmonton, Montreal, and Vancouver, savings in heating energy use were about 10%. Cooling energy can be totally offset in Edmonton and Vancouver, and average savings of 35% can be achieved in Montreal.
Akbari, H., Davis, S., Dorsano, S., Huang, J., Winnett, S. 1992. Cooling Our Communities: A Guidebook on Tree Planting and Light-colored Surfacing. Lawrence Berkeley Lab, LBL-31587. US EPA Policy, Planning and Evaluation Jan. 1992 (PM-221).
Abstract: This book is a practical guide that presents the current state of knowledge on potential environmental and economic benefits of strategic landscaping and altering surface colors in our communities. The guidebook, reviews the causes, magnitude, and impacts of increased urban warming, then focuses on actions by citizens and communities that can be undertaken to improve the quality of our homes and towns in cost-effective ways.
Akbari, H., Kurn, D.M., Bretz, S.E., Hanford, J.W. 1997. Peak Power and Cooling Energy Savings of Shade Trees. Energy and Buildings, 25(2), 139-148.
Abstract: In summer of 1992, we monitored peak power and cooling energy savings from shade trees in two houses in Sacramento, CA. The collected data include air-conditioning electricity use, indoor and outdoor dry bulb temperatures and humidities, roof and ceiling surface temperatures, inside and outside wall temperatures, insolation, and wind speed and direction. Shade trees at the two monitored houses yielded seasonal cooling energy savings of 30%, corresponding to an average daily savings of 3.6 and 4.8 kWh/d. Peak demand savings for the same houses were 0.6 and 0.8 kW (about 27% savings in one house and 42% in the other). The monitored houses were modeled with the DOE-2.1E simulation program. The simulation results underestimated the cooling energy savings and peak power reductions by as much as twofold.
Akbari, H., Pomerantz, M., Taha, H. 2001. Cool Surfaces and Shade Trees to Reduce Energy Use and Improve Air Quality in Urban Areas. Solar Energy, 70(3), 295-310.
Abstract: Elevated summertime temperatures in urban 'heat islands' increase cooling-energy use and accelerate the formation of urban smog. Except in the city’s core areas, summer heat islands are created mainly by the lack of vegetation and by the high solar radiation absorptance by urban surfaces. Analysis of temperature trends for the last 100 years in several large U.S. cities indicate that, since ∼1940, temperatures in urban areas have increased by about 0.5–3.0°C. Typically, electricity demand in cities increases by 2–4% for each 1°C increase in temperature. Hence, we estimate that 5–10% of the current urban electricity demand is spent to cool buildings just to compensate for the increased 0.5–3.0°C in urban temperatures. Downtown Los Angeles (L.A.), for example, is now 2.5°C warmer than in 1920, leading to an increase in electricity demand of 1500 MW. In L.A., smoggy episodes are absent below about 21°C, but smog becomes unacceptable by 32°C. Because of the heat-island effects, a rise in temperature can have significant impacts. Urban trees and high-albedo surfaces can offset or reverse the heat-island effect. Mitigation of urban heat islands can potentially reduce national energy use in air conditioning by 20% and save over $10B per year in energy use and improvement in urban air quality. The albedo of a city may be increased at minimal cost if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads. Similar incentive-based programs need to be developed for urban trees.
Akbari, H. 2002. Shade Trees Reduce Building Energy Use and CO2 Emissions from Power Plants. Environmental Pollution, 116(Suppl. 1), S119-S126.
Abstract: Urban shade trees offer significant benefits in reducing building air-conditioning demand and improving urban air quality by reducing smog. The savings associated with these benefits vary by climate region and can be up to $200 per tree. The cost of planting trees and maintaining them can vary from 10 to $500 per tree. Tree-planting programs can be designed to have lower costs so that they offer potential savings to communities that plant trees. Our calculations suggest that urban trees play a major role in sequestering CO2 and thereby delay global warming. We estimate that a tree planted in Los Angeles avoids the combustion of 18 kg of carbon annually, even though it sequesters only 4.5-11 kg (as it would if growing in a forest). In this sense, one shade tree in Los Angeles is equivalent to three to five forest trees. In a recent analysis for Baton Rouge (Louisiana), Sacramento (California), and Salt Lake City (Utah), USA, we estimated that planting an average of four shade trees per house (each with a top view cross section of 50 m2) would lead to an annual reduction in carbon emissions from power plants of 16 000, 41 000 and 9000 tons, respectively (the per-tree reduction in carbon emissions is about 10-11 kg per year). These reductions only account for the direct reduction in the net cooling- and heating-energy use of buildings. Once the impact of the community cooling is included, these savings are increased by at least 25%.
Arendt, R. G., (Ed.). 1997. Putting Conservation into Local Codes. Growing Greener, Natural Lands Trust, Inc. Media, PA 19063.
Abstract: This booklet summarizes how municipalities can use the development process to their advantage to protect interconnected networks of open space: natural areas, greenways, trails and recreational land. Four basic actions underlie the Growing Greener process: Envision the future with community audits; protect open space networked through conservation planning; conservation zoning choices; conservation subdivision design process.
Armson, D., Stringer, P., Ennos, A.R. 2012. The Effect of Tree Shade and Grass on Surface and Globe Temperatures in an Urban Area. Urban Forestry & Urban Greening, 11(3), 245-255.
Abstract: The process of urbanization alters the thermal balance of an area resulting in an urban heat island effect where cities can be several degrees centigrade warmer than the surrounding rural landscape. This increased heat can make cities uncomfortable places and, during heat waves, can pose serious health risks. This study looked at the role that trees and grass can play in reducing regional and local temperatures in urban areas during the summer within the urban landscape of Manchester, UK. In June and July 2009 and 2010, we monitored the surface temperatures of small plots composed of concrete and grass in the presence or absence of tree shading, and measured globe temperatures above each of the surfaces. The same measures were also recorded at mid-day on larger expanses of asphalt and grass in an urban park. Both surface and shade greatly affected surface temperatures. Grass reduced maximum surface temperatures by up to 24 °C, similar to model predictions, while tree shade reduced them by up to 19 °C. In contrast, surface composition had little effect upon globe temperatures, whereas shading reduced them by up to 5–7 °C. These results show that both grass and trees can effectively cool surfaces and so can provide regional cooling, helping reduce the urban heat island in hot weather. In contrast grass has little effect upon local air or globe temperatures, so should have little effect on human comfort, whereas tree shade can provide effective local cooling.
Armson, D., Rahman, M.A., Ennos, A.R. 2013. A Comparison of the Shading Effectiveness of Five Different Street Tree Species in Manchester, UK. Arboriculture & Urban Forestry, 39(4), 157-164.
Abstract: One major benefit of urban trees is the shade they provide on sunny days; this reduces the heat stored in engineered surfaces and lowers the heat load on people, increasing their comfort. This study compared the shading effectiveness of five small street tree species within the urban landscape of Manchester, UK. The area of shade produced by each tree during early and midsummer 2012 was calculated from morphological measurements, such as canopy height, width, and aspect ratio. The effect of tree shade on air, mean radiant and surface temperatures was also compared and related to the leaf area index (LAI) of the canopy. It was found that tree shade reduced mean radiant temperatures by an average of 4°C, though neither tree species nor LAI had a significant effect. Tree shade reduced surface temperatures by an average of 12°C, and the tree species and LAI both had significant effects. Tree species with higher LAI, Crataegus laevigata and Pyrus calleryana, provided significantly more cooling than the other species, and surface temperature reduction was positively correlated with LAI. This study has shown that trees are useful in improving both human thermal comfort and reducing surface temperatures in urban areas, and that selection of tree species with high LAI can maximize the benefits they provide.
Arnold, C.L., Gibbons, C.J. 1996. Impervious Surface Coverage: the Emergence of a Key Environmental Indicator. Journal of the American Planning Association, 62(2), 243-258.
Abstract: Planners concerned with water resource protection in urbanizing areas must deal with the adverse impacts of polluted runoff. Impervious surface coverage is a quantifiable land-use indicator that correlates closely with these impacts. Once the role and distribution of impervious coverage are understood, a wide range of strategies to reduce impervious surfaces and their impacts on water resources can be applied to community planning, site-level planning and design, and land use regulation. These strategies complement many current trends in planning, zoning, and landscape design that go beyond water pollution concerns to address the quality of life in a community.
Bernatzky, A. 1982. The Contribution of Tress and Green Spaces to a Town Climate. Energy and Buildings, 5(1), 1-10.
Abstract: The urban climate is deprived of its natural characteristics in many ways. Trees and open spaces make an important contribution to the improvement of the artificial climate of towns. They lower the temperature considerably by evaporative cooling. A beech forest evaporates 83.8% of its radiated energy serves to warm the air. A small green area in Frankfurt which lowered the temperature by 3 - 3.5 °C and intensified the relative humidity by 5 - 10% ventilated the overheated, dirty, and polluted town center and provided fresh air. Parks are able to filter up to 80% of the pollution from the air, and trees in avenues by up to 70%. Even without leaves (in winter) the plants still retain 60% of their efficiency: they reduce the lead content of the air, reduce noise by up to 12 dB and provide a supply of oxygen under calm weather conditions. In consequence, grassed areas and trees should be planted more systematically in towns.
Bowler, D.E., Buyung-Ali, L., Knight, T.M., Pullin, A.S. 2010. Urban Greening to Cool Towns and Cities: A Systematic Review of the Empirical Evidence. Landscape and Urban Planning, 97(3), 147-155.
Abstract: 'Urban greening' has been proposed as one approach to mitigate the human health consequences of increased temperatures resulting from climate change. We used systematic review methodology to evaluate available evidence on whether greening interventions, such as tree planting or the creation of parks or green roofs, affect the air temperature of an urban area. Most studies investigated the air temperature within parks and beneath trees and are broadly supportive that green sites can be cooler than non-green sites. Meta-analysis was used to synthesize data on the cooling effect of parks and results show that, on average, a park was 0.94 °C cooler in the day. Studies on multiple parks suggest that larger parks and those with trees could be cooler during the day. However, evidence for the cooling effect of green space is mostly based on observational studies of small numbers of green sites. The impact of specific greening interventions on the wider urban area, and whether the effects are due to greening alone, has yet to be demonstrated. The current evidence base does not allow specific recommendations to be made on how best to incorporate greening into an urban area. Further empirical research is necessary in order to efficiently guide the design and planning of urban green space, and specifically to investigate the importance of the abundance, distribution and type of greening. Any urban greening programme implemented would need to be appropriately designed and monitored to continue to evaluate benefit to human health through reducing temperature.
Carver, A.D., Unger, D.R., Parks, C.L. 2004. Modeling Energy Savings from Urban Shade Trees: An Assessment of the CITYgreen® Energy Conservation Module. Environmental Management, 34(5), 650-655.
Abstract: CITYgreen® software has become a commonly used tool to quantify the benefits of urban shade trees. Despite its frequent use, little research has been conducted to validate results of the CITYgreen energy conservation module. The first objective of this study is to perform a familiar application of CITYgreen software to predict the potential energy savings contribution of existing tree canopies in residential neighborhoods during peak cooling summer months. Unlike previous studies utilizing CITYgreen, this study also seeks to assess the software’s performance by comparing model results (i.e., predicted energy savings) with actual savings (i.e., savings derived directly from energy consumption data provided by the electric utility provider). Homeowners in an older neighborhood with established trees were found to use less energy for air-conditioning than homeowners in a recently developed site. Results from the assessment of model performance indicated that CITYgreen more accurately estimated the energy savings in the highly vegetated, older neighborhood.
Cantón, M.A., Cortegoso, J.L., de Rosa, C. 1994. Solar Permeability of Urban Trees in Cities of Western Argentina. Energy and Buildings, 20(3), 219-230.
Abstract: The extensive use of trees in urban environments is a common feature of many cities of the temperature mid-latitude arid zones of western Argentina. Although beneficial in summer, trees can reduce solar access in urban buildings to an important extent. Permeability to solar radiation of the crowns of the most commonly used deciduous trees in the city of Mendoza was measured throughout their yearly foliation cycle. Results of permeabilities of four species of trees to global, diffuse and direct radiation are presented, for different zones, of their canopies and at typical stages of their annual cycle. Discussion of results and proposals for future research are also included.
Davey Research Group. 1993. Updating Research Data on the Benefits and Costs of the Urban Forestry for Enhanced Technology Transfer in the Southern Region. Davey Resource Group, Irvine, California 92714.
Abstract: The updates list the research topics (list) reviewed and the issues and topics needing further research including: environmental functions such as air quality, energy use, carbon storage and storm water; and the socioeconomic functions of property value, environmental perception, urban wildlife and tree program costs.
DeWalle, D.R., Heisler, G.M. 1983. Windbreak Effects on Air Infiltration and Space Heating in a Mobile Home. Energy and Buildings, 5(4), 279-288.
Abstract: During winter experiments in central Pennsylvania a windbreak, 61 meters long and composed of a single row of white pine trees, significantly reduced air infiltration rates and space heating energy needs in a small mobile home by up to 54% and 18%, respectively. Greatest reductions in air infiltration rates occurred with the home at one windbreak height (1H) downwind, even though maximum reductions in wind velocity occurred at 2H or 4H downwind. Space heating energy savings were less sensitive to downwind position, with maximum energy savings measured at both 1H and 2H. Maximum energy savings due to the windbreak for an entire winter heating season were estimated to be 12%.
DeWalle, D.R., Heisler, G.M., Jacobs, R.E. 1983. Forest Home Sites Influence Heating and Cooling Energy. Journal of Forestry, 81(2), 84-88.
Abstract: Experiments with small mobile homes in Pennsylvania indicated that shade of trees can significantly reduce solar heating and that by lowering wind speeds forests can lessen infiltration of outside air. In one deciduous stand in summer, cooling energy needs were 75 percent less than in the open. In winter shading is counterproductive, offsetting savings from reduced infiltration of cold air. In the deciduous stand, savings in winter heating energy were only 8 percent, and with greater shading in a dense pine forest heating energy needs rose 12 percent. Forests and windbreaks are especially effective with poorly sealed houses and in windy weather. On forested sites in most of the United States, energy use can probably be lessened by manipulating forest growth to allow the sun to strike the house in winter. On open sites windbreaks and carefully located shade trees would lessen year-round energy use.
Donovan, G.H., Butry, D.T. 2009. The value of shade: Estimating the effect of urban trees on summertime electricity use. Energy and buildings, 41(6), 662-668.
Abstract: We estimated the effect of shade trees on the summertime electricity use of 460 single-family homes in Sacramento, California. Results show that trees on the west and south sides of a house reduce summertime electricity use, whereas trees on the north side of a house increase summertime electricity use. The current level of tree cover on the west and south sides of houses in our sample reduced summertime electricity use by 185 kWh (5.2%), whereas north-side trees increased electricity use by 55 kWh (1.5%). Results also show that a London plane tree, planted on the west side of a house, can reduce carbon emissions from summertime electricity use by an average of 31% over 100 years.
Dwyer, J.F., McPherson, E.G., Schroeder, H.W., Rowntree, R.A. 1992. Assessing the benefits and costs of the urban forest. Journal of Arboriculture, 18(5), 227-234.
Abstract: With effective planning and management, urban trees and forests will provide a wide range of important benefits to urbanites. These include a more pleasant, healthful, and comfortable environment to live, work, and play in, savings in the costs of providing a wide range of urban services, and substantial improvements in individual and community well-being. Urban forestry plans should begin with consideration of the contribution rat trees and forests can make to people's needs. Planning and management efforts should focus on how the forest can best meet those needs. Past planning and management efforts have not been as effective as they might have been because planners and managers have under estimated the potential benefits that urban trees and forests can provide, and have not understood the planning and management efforts needed to provide those benefits, particularly the linkages between benefits and characteristics of the urban forest and its management.
Ewing, R., Rong, F. 2008. The Impact of Urban Form on U.S. Residential Energy Use. Housing Policy Debate, 19(1), 1-30.
Abstract: While the impact of urban form on transportation energy use has been studied extensively, its impact on residential energy use has not. This article presents a conceptual framework linking urban form to residential energy use via three causal pathways: electric transmission and distribution losses, energy requirements of different housing stocks, and space heating and cooling requirements associated with urban heat islands. Two of the three can be analyzed with available national data. After we control for other influences, residents of sprawling counties are more likely to live in single‐family detached houses than otherwise comparable residents of compact counties and also more likely to live in big houses. Both lead to higher residential energy use. Because of the urban heat island effect, residents of sprawling counties across the nation on average pay a small residential energy penalty relative to residents of compact counties. Implications for urban planning are explored.
Fahmy, M., Sharples, S., Yahiya, M. 2010. LAI Based Trees Selection for Mid Latitude Urban Developments: a Microclimatic Study in Cairo, Egypt. Building and Environment, 45(2), 345-357.
Abstract: To study the leaf area index, LAI, based thermal performance in distinguishing trees for Cairo's urban developments, ENVI-met plants database was used as platform for a foliage modeling parameter, the leaf area density, LAD. Two Egyptian trees; Ficus elastica, and Peltophorum pterocarpum were simulated in 2 urban sites with one having no trees, whilst the second is having Ficus nitida trees. Trees LAD values were calculated using flat leaves' trees LAI definition to produce maximum ground solid shadow at peak time. An empirical value of 1 for LAI is applied to numerically introduce LAD values for ENVI-met. Basically, different meteorological records showed improvements for pedestrian comfort and ambient microclimate of the building using F. elastica. About 40–50% interception of direct radiation, reductions in surfaces' fluxes around trees and in radiant temperature Tmrt in comparison to base cases gave preferability to F. elastica. The lack of soil water prevented evapotranspiration to take place effectively and the reduced wind speeds concluded negligible air temperature differences from both base cases except slightly appeared with the F. elastica. Results show that a flat leaves tree if does not validate LAI of 1, the ground shading would not fulfill about 50% direct radiation interception and this value can be used as a reference for urban trees selection. Further simulations were held to investigate LAI value of maximum direct radiation interception. Performing additional simulations, F. elastica of LAI of 3 intercepted almost 84% of direct radiation and revealed implications about urban trees in practice and its actual LAI.
Federer, C.A. 1976. Trees Modify the Urban Microclimate. Journal of Arboriculture, 2(7), 121-127.
Abstract: A person's feeling of thermal comfort is affected by environmental conditions, including solar radiation, air temperature, wind, humidity, long wave radiation, and precipitation. Trees modify all of these variables and therefore affect individual thermal comfort. Shade and wind protection are well recognized efforts. But trees and other vegetation also contribute to cooling the air by the evaporative process of transpiration. An urban shade tree can produce as much cooling as five room air conditioners running 20 hours a day. The lack of transpiring vegetation in cities is one reason why cities are often several degrees hotter than the surrounding countryside.
Gardener, T.J., Sydnor, T.D. 1984. Interception of summer and winter Insolation by five shade tree species. The Journal of the American Society for Horticultural Science, 109, 448-450.
Abstract: Five species of ornamental trees were examined with an Eppley pyranometer for interception of total solar radiation between 380 nm and 1100 nm. Measurements were made at the northern dripline and expressed as percentage of shade. Trees were selected for varying forms, branch and canopy densities. Mean percentage of shade for the fully foliaged and leafless canopies, respectively, were Pyrus calleryana 'Chanticleer' 75% and 43%, Acer rubrum 'Red Sunset' 69% and 25%, Zelkova serrata 'Village Green' 61% and 24%, Gymnocladus dioicus 60% and 15%, and Gleditsia triacanthos inermis 'Moraine' 56% and 21%. No statistically significant (PSO.05) correlation was observed among solar radiation intercepted and photosynthetically active radiation (PAR) intercepted, pathlength, silhouette area and canopy volume. Growth habit did not affect shading capacities significantly.
Georgi, J.N., Dimitriou, D. 2010. The Contribution of Urban Green Spaces to the Improvement of Environment in Cities: Case Study of Chania, Greece. Building and Environment, 45(6), 1401-1414.
Abstract: This paper investigates how vegetation, mainly through evapotranspiration, affects the improvement of microclimatic conditions in urban areas and, more specifically, it examines the case for the city of Chania in Crete. The objectives of this study are to examine the bioclimatic role of green areas in urban sites as they affect the thermal comfort of residents, and to study the cross-correlation of factors that participate in this process. To achieve these objectives, we have examined the parameters that contribute to the microclimate of a space and consider how it is influenced by vegetation. In addition, we have analyzed the effect of vegetation with respect to evapotranspiration, and have recorded the existing vegetation of Chania city and the relationship with the geomorphologic and urban characteristics of the city. This has involved calculating the evapotranspiration of various plant species, and collecting measurements at various places in Chania. These studies are designed to determine the cause of the changes of thermal comfort in different parts of the city, and to examine the differentiation of thermal comfort that is observed between different plant species with respect to the evapotranspiration measure that has been calculated for each of them. The intention of this work is to aid efforts to improve the environment of Chania through better planning and the appropriate choice of the species used for planting open spaces. Finally, it is hoped that the results of this work will be of use in planning the environments of spaces in other cities that have similar characteristics.
Gómez-Muñoza, V.M., Porta-Gándarab, M.A., Fernándezc, J.L. 2010. Effect of Tree Shades in Urban Planning in Hot-arid Climatic Regions. Landscape and Urban Planning, 94(3-4), 149-157.
Abstract: The present study is carried out for dry hot climate places, where excessive solar heating is felt throughout the year. The effect of tree shadowing buildings is found to reduce heating loads; hence trees have a beneficial effect in energy economics. The emerging economic value of tree shadows in hot climate cities grants the development of an appropriate simulation numerical method to establish relative advantages on energy savings related to dwelling envelopes. The results demonstrate that large trees can provide up to 70% shade during spring and autumn, thus saving a very large amount of energy along the whole year. Hence, economic value of larger trees is greater than that of younger species.
Greene, C.S., Millward, A.A., Ceh, B. 2011. Who is likely to plant a tree? The use of public socio-demographic data to characterize client participants in a private urban forestation program. Urban Forestry & Urban Greening, 10(1), 29-38.
Abstract: City trees, and the ecosystems of which they are a part, provide important benefits to urban residents. In many cities across North America, suitable locations for the planting of trees – expansion of the urban forest – are mostly confined to privately owned land. Our primary motivation for conducting this study was to investigate whether aggregate socio-demographic characteristics, represented geographically by census tract, have explanatory value concerning participation in a large urban forestation program. Specifically, we used 2006 Statistics Canada census data and known geographic locations of participants in a privately administered urban forestation program to conduct a two-stage multiple regression analysis for East York, Etobicoke, Markham, North York, Scarborough, Toronto, and York (all densely populated centers within the Greater Toronto Area of southern Ontario, Canada). A priori assumptions about program participants were evaluated first based on a review of the literature and through solicitation of expert opinion. The second step employed an exploratory data analysis approach to identify variables that may have differed from a priori assumptions. Results indicate that there are marked regional differences in both the a priori assumptions, as well as in the variables identified through the exploratory regression analysis. The explanatory ability of the baseline regression model is strongest for East York and weakest for Markham, whereas the ability to explain program participation using the exploratory regression model is strongest for Markham and weakest for North York. While participation of Toronto and York residents is largely explained by a dwelling-specific variable (the number of homes constructed pre-1946), the participation of Markham residents is typified by a gender-specific income variable (the number of females reporting a gross income range of $50 to <$60k). Beyond provision of location-specific client information, our study presents a methodological framework that is of value to the refinement of current forestation efforts and to future target marketing of similar initiatives.
Hafner, J., Kidder, S.Q. 1989. Urban Heat Island Modeling in Conjunction with Satellite-Derived Surface/Soil Parameters. Journal of Applied Meteorology and Climatology, 38(4), 448-465.
Abstract: The main purpose of this work is to improve UHI modeling by using AVHRR (Advanced Very High Resolution Radiometer) satellite data to retrieve the surface parameters. A hydrostatic three-dimensional mesoscale model was used to perform the numerical modeling. The net urban effect was determined as the difference between urban and nonurban simulations, in which urban parameters were replaced by rural parameters. Two winter days were each used for two numerical simulations: a control and an urban-to-rural replacement run. Moisture availability values on the less windy day showed generally a south to north gradient downwind of the city and urban values less than rural values (the urban dry island day). Moisture availability was higher on the windy day, with uniform values in the rural and urban areas (uniform soil moisture day). The observed lack of corresponding urban change is expected, as its thermal inertia values depend more on urban building materials than on moisture of soil. In both cases both the 2-m and surface skin UHIs showed positive values at night and negative values (an urban cool island, UCI) during the day. The larger nighttime 2-m UHI was on the dry day (0.8° vs 0.6°C), while the larger daytime 2-m UCI was on the moist soil day (−0.3° vs −0.5°C). Note that the surface differences were almost always greater than the 2-m differences. These day–night differences imply a rural thermal inertia lower than its urban values on both days, which is in conflict with the observations on the wet uniform soil moisture day. On the uniform thermal inertia day (wet day), both the UHI and UCI amplitudes should be less than on the other day, but this is not the case. A possible explanation for both of these conflicts is the improper influence of the urban plume on this day on lowering the thermal inertia and moisture availability values used in the replacement urban simulation.
Heisler, G.M. 1974. Trees and Human Comfort in Urban Areas. Journal of Forestry, 72(8), 466-469.
Abstract: The most important contribution of trees to amelioration of urban microclimate is in interception of solar radiation. Shielding of long-wave radiation by trees has usually been underemphasized. Transpiration by trees may be important in urban energy budgets, but the total effect of transpiration by city trees is not well understood. Use of trees for control of air flow requires care because in summer increased wind speed is desired, but in winter trees can greatly increase human comfort by reducing wind speed. Metabolism and photosynthesis by trees have no significant impact on microclimate.
Heisler, G.M. 1977. Trees Modify Metropolitan Climate and Noise. Journal of Arboriculture, 3(11), 201-207.
Abstract: Human comfort in urban areas is altered by trees primarily through their influence on the exchange of radiant energy — both solar and long-wave. Although urban trees probably use large amounts of heat for transpiration, this process does not result in significantly cooler air in the vicinity of single or small groups of trees. Even low winds quickly disperse the cooled air. Outdoor spaces that receive heavy pedestrian use should be made as versatile as possible by providing both sunny and shady sites for sitting and walking. Windbreaks may reduce energy requirements for heating buildings by 10 to 25 percent. Although shade obviously is a benefit in summer; winter shade is a disadvantage, and even deciduous-tree shade is significant in winter. Trees are useful for noise control primarily because they scatter sound waves, which are then absorbed by the ground. Dense forests or plantings of trees can reduce transmission of traffic noise, but if highways carrying high-speed truck traffic pass through residential areas, tree barriers alone cannot reduce sound levels to an acceptable maximum within about 350 feet of the highway.
Heisler, G.M. 1986. Effects of Individual Trees on the Solar Radiation Climate of Small Buildings. Urban Ecology, 9(3-4), 337-359.
Abstract: Under clear skies, a mid-sized sugar maple tree (Acer saccharum Marsh.) reduced irradiance in its shade on a south-facing wall by about 80% when in leaf, and by nearly 40% when leafless. Reductions by a similar-sized London plane (Platanus acerifolia W.) were generally slightly smaller. The percentage reductions varied with the fraction (DR) of diffuse radiation, and could be approximated by regressions with DR2 as the independent variable.
The significance of the irradiance reductions for building radiation climate was tested by using physical models of representative tree crowns (similar to sugar maple) and a representative house to evaluate shadow patterns, along with a mathematical model of average hourly solar radiation for an average day of each month. For a mid-sized tree with a 2-m clear bole located south of the house in a cloudy climate, the ratio of desirable insolation reductions during the cooling season to undesirable insolation reductions during the heating season was a low 0.74; whereas, with the same tree on the west, the ratio was a much more beneficial 4.6. In a sunny climate, the ratios were 0.55 and 3.3 for the tree on the south and west, respectively. A taller tree with a longer clear bole on the south produced more favorable ratios of cooling season to heating season insolation reductions than the tree with the short clear bole on the south.
Heisler, G.M. 1986. Energy Savings with Trees. Journal of Arboriculture, 12(5), 113-125.
Abstract: In conventional buildings, trees increase, decrease, or have little effect on energy use depending on general climate, building type, tree species, and tree location. Tree arrangements that save energy provide shade primarily for east and west walls and roofs and wind protection from the direction of prevailing winter winds. Particularly for buildings specially designed to use solar energy and those with solar collectors, it is important to place tree crowns so they do not block sun from collectors and south walls. But conventional houses also benefit from winter sun. Deciduous trees provide better year-round shade than conifers, but do reduce solar energy significantly even without leaves. In winter, reductions in solar energy on south walls by a deciduous tree may be greater than reductions by the same tree in summer. Hence, growth rate and crown shape are important criteria in selecting shade trees, and the placement of trees around the house is important. A summary of research data suggests that the maximum potential annual effect of trees on energy use in conventional houses is about 20 to 25% compared to the same house in the open.
Heisler, G.M. 1990. Mean Wind Speed below Building Height in Residential Neighborhoods with Different Tree Densities. ASHRAE Transactions, 96(1), 1389-1396.
Abstract: There is little available knowledge of the absolute or relative effects of trees and buildings on wind at or below building height in residential neighborhoods. In this study, mean wind speed was measured at a height of 6.6 ft (2 m) in neighborhoods of single-family houses. Building densities ranged between 6% and 12% of the land area, and tree-cover densities were between 0 and 77%. Measurements were made with cup anemometers at points either 1/2 or 1 building height from 15 sample houses. An anemometer at 6.6 ft at a local airport provided the reference wind speed, Uo. Approach wind speeds toward houses in 8 neighborhood with no trees were reduced an average of 22% compared to Uo. In a neighborhood with similar building density and 77% tree density, reductions in approach wind by both trees and buildings averaged 65% in winter and 70% in summer. Empirical models were derived to predict the effect of trees on wind separately from the effect of buildings. The models were based on tree and building geometry derived from map measurements, aerial photos, and fisheye photos from wind-measuring points.
Henry, J.A., Dicks, S.E. 1987. Association of Urban Temperatures with Land Use and Surface Materials. Landscape and Urban Planning, 14, 21-29.
Abstract: This paper shows the correlations of urban-rural temperatures in Lawrence, Kansas, with land-use types and surface materials. Temperatures were acquired at 168 points using the auto-traverse technique on 15 mornings, afternoons and evenings in late summer-early autumn. The relationships of these 45 detailed temperature patterns with 12 land-use types and 10 surface materials over the entire city and adjacent rural areas show that the land-use types most frequently associated with temperature patterns are residential, commercial (including the CBD) and undeveloped. Among the surface materials, surface asphalt, asphaltic roofing and water are related most often to temperatures. Several of these findings corroborate many results of previous urban numerical simulation modeling analyses.
Heynen, N.C. 2003. The Scalar Production of Injustice within the Urban Forest. Antipode, 35(5), 980-998.
Abstract: Research has recently argued, quite successfully, for a more dialectic appreciation of urban nature/society relations. Despite this progress, there is still the need to recognize that the social production of urban environments explicitly leads to uneven urban environments and environmental injustice. Environmental inequalities clearly exist within cities; when taking into account how environmental externalities play out at different scales, the degree to which something is unjust becomes less clear. This paper discusses how the scales at which socially produced urban forest externalities play out pose difficulties for considering environmental injustice. This issue, while interesting from the point of view of considering scalar nature/social dialects, also makes policy considerations for urban reforestation problematic as a result of the ways in which urban forests contribute to local/global ecological scenarios.
Heynen, N., Perkins, H. A. and Roy, P. 2006. The Political Ecology of Uneven Urban Green Space (The Impact of Political Economy on Race and Ethnicity in Producing Environmental Inequality in Milwaukee). Urban Affairs Review 42 (1): 3-25.
Abstract: This article investigates the role of urban political economy, private-public property relations, and race and ethnicity in the social production of Milwaukee's urban forest. By integrating urban-forest canopy-cover data from aerial photography, United States Census data, and qualitative data collected through in-depth interviews, this analysis suggests that there is an inequitable distribution of urban canopy cover within Milwaukee. Since urban trees positively affect quality of life, the spatially inequitable distribution of urban trees in relation to race and ethnicity is yet another instance of urban environmental inequality that deserves greater consideration in light of contemporary and dynamic property relations within capitalist societies.
Higuchi, Y., Udagawa, M. 2007. Effects of Trees on the Room Temperature and Heat Load of Residential Building. Building Simulation, Beijing, China. International Building Performance Simulation Association (IBPSA). pp. 223-230.
Abstract: In summer, the shady planting is expected for providing shadow on building envelope and reducing reflected solar radiation from the front yard. The heat load simulation program which can take into consideration the shadow effects caused by trees including the effect of the long wave radiation exchange is developed by the authors. The program used to examine the effects of trees on the room thermal environment as well as heating and cooling loads of a model house. In the simulation, two kinds of trees, evergreen broad-leaved tree and deciduous broad-leaved tree were assumed. The simulation results for several cases of tree arrangements around the house showed that the cooling load was reduced by 15% - 20%. While the difference in cooling load was small, the heating load increased by 26% and 8.5% in case of the evergreen broad-leaved tree and the deciduous broad-leaved tree, respectively.
Hildebrandt, E.W., Kallet, R., Sarkovich, M., Sequest, R. 1996. Maximizing the Energy Benefits of Urban Forestation. The 1996 Summer Study on Energy Efficiency in Buildings, "Profiting from Energy Efficiency", Washington, DC. American Council for an Energy Efficient Economy (ACEEE). pp. 9.123-9.131.
Abstract: This paper examines key issues involved in evaluating beneﬁts of tree planting programs from the perspective of electric utilities, as well as from a wider perspective of public and private entities that may beneﬁt from such programs. The nation’s largest shade tree program, sponsored by the Sacramento Municipal Utility District (SMUD) in collaboration with the Sacramento Tree Foundation (STF), is used as a case study. Results of a recent analysis of the energy beneﬁts of SMUD's Shade Tree Program are presented, along with program modifications being implemented to improve program cost-effectiveness. A sensitivity analysis of the relative importance of major uncertainties surrounding the beneﬁts of the Shade Tree Program is presented, and priorities for future research are discussed.
Hildebrandt, E.W., Sarkovich, M. 1998. Assessing the Cost-Effectiveness of SMUD's Shade Tree Program. Atmospheric Environment, 32(1), 85-94.
Abstract: This paper examines key issues involved in evaluating benefits (avoided cost of energy and capacity) of tree planting programs from the perspective of electric utilities, as well as from a wider perspective of public and private entities that may benefit from such programs. The nation's largest shade tree program, sponsored by the Sacramento Municipal Utility District (SMUD) in collaboration with the Sacramento Tree Foundation (STF), is used as a case study. Results of a recent analysis of the energy benefits of SMUD's Shade Tree Program are presented, along with program modifications being implemented to improve program cost-effectiveness. A sensitivity analysis of the relative importance of major uncertainties surrounding the benefits of the Shade Tree Program is presented, and priorities for future research are discussed. This article presents findings from a study on residential development patterns and urban heat island formation in the Atlanta, Georgia, metropolitan region. High-resolution thermal imagery collected by the National Aeronautical and Space Administration (NASA) is used in conjunction with parcel-level tax records to examine the interaction between the design of single-family residential parcels and the emission of radiant heat energy. Results from a path analysis illustrate that lower density patterns of residential development contribute more radiant heat energy to surface heat island formation than higher density development patterns within the Atlanta region. Compact moderate-to-high- density new construction and area-based tree ordinances are recommended as policy strategies for mitigating the effects of urban development on regional climate change.
Hongbing, W., Jun, Q., Yonghong, H., Li, D. 2010. Optimal Tree Design for Daylighting in Residential Building. Building and Environment, 45(12), 2594-2606.
Abstract: Urban reforestation is advocated as an efficient countermeasure to the intensification of urban heat islands. The greening and beautification of residential quarters is one of the main concerns of residents, while lighting and ventilation are two main energy-consuming building services. Hence, the tree layout in green space between buildings is important, and it is necessary to determine the relationships between trees and buildings. This study takes Shanghai as a case study to optimize tree design between residential buildings and meet good daylighting requirements. Models were made using software such as AutoCAD and SketchUp. The relationships between maximum tree height and building separation were determined. For the same building layout, there were different tree height limits according to crown shape; the order of decreasing height limits was cylindrical, conical, spherical, and inverted conical crowns. Three cases having different green space between building layouts were studied. Their maximum tree heights differed. Overall, our model helps us realize good daylighting of a building environment. The formula allows us to determine which trees to plant between buildings in that we can predict the effects of future tree growth on building daylighting.
Hoyano, A. 1984. Relationships between the Type of Residential Area and the Aspects of Surface Temperature and Solar Reflectance. Energy and Buildings 7(2): 159-173.
Abstract: To document the relationships between the basic parameters for environmental planning, such as land use, and the thermal environment in Japan, the article presents a study of aspects of seasonal conditions and solar heat balance. Using information of radiation observed by multispectral scanners (MSS) compared with information obtained through terrestrial surveys, radiation characteristics are compared for (a) the type of residential areas and (b) the land coverage conditions and the changes of these aspects in winter and summer environments.
Hoyano, A., Iino, A., Ono, M., Tanighchi, S. 1999. Analysis of the Influence of Urban Form and Materials on Sensible Heat Flux — a Case Study of Japan's Largest Housing Development "Tama New Town". Atmospheric Environment, 33(24-25), 3931-3939.
Abstract: In this study, the relationship between the form and materials of urban blocks and sensible heat flux from total surfaces was analyzed in the case of `Tama New Town', which is one of the largest housing developments in Japan and is under continuing development. First, urban blocks were divided into five categories depending on the building plot types. The characteristics of the form and thermal properties of each building, as well as the land cover condition (area of vegetation, bare soil, asphalt pavement, and built area) of each category was considered. Furthermore, 6 urban blocks were selected for numerical simulation of heat balance of the total surfaces, and sensible heat flux from the total surfaces of each urban block on clear sky summer day was calculated. It was confirmed that the influence of the direction that buildings faced and floor area ratio was as great as that of building materials upon the amount of sensible heat flux in each urban block.
Huang, Y.J., Akbari, H., Taha, H., Rosenfeld, A.H. 1987. The Potential of Vegetation in Reducing Summer Cooling Loads in Residential Buildings. Journal of Applied Meteorology and Climatology, 26(9), 1103-1116.
Abstract: The potential of trees and other vegetation to reduce building cooling loads has been recorded in a number of studies but the meso- and microclimate changes producing such savings are not well understood. This paper describes a preliminary attempt to model the effects of landscaping on temperature, humidity, wind speed and solar gain in urban climates using information from existing agricultural and meteorological studies, with particular attention placed on quantifying the effects of plant evapotranspiration. The climate model is then used in conjunction with the DOE-2.1C building simulation program to calculate the net reductions in air-conditioning requirements due to trees and other vegetation. There are additional benefits in lowering peak power consumption, where the savings are as much as 34% in Sacramento, 18% in Phoenix, 22% in Lake Charles, and 44% in Los Angeles. Parametric analysis reveals that most of the savings can be attributed to the effects of increased plant evapotranspiration, and only 10% to 30% to shading. The energy penalties of reduced wind speeds are found to be small in all four locations. The preliminary results suggest that while the conservation benefits of planting trees are appreciable at the individual house level, equally dramatic savings can be realized at the urban level through modifications of the urban climate by increasing the total amount of vegetative cover. Such a conservation strategy may be elective in counteracting the summer heat island evident in cities and may improve ambient conditions as well as reduce summertime air-conditioning requirements.
Huang, Y.J., Akbari, H., Taha, H. 1990. The Wind-shielding and Shading Effects of Trees on Residential Heating and Cooling Requirements. ASHRAE Transactions, 96, 1403-1411.
Abstract: The US Department of Energy (DOE) has funded several research projects, including this study, to assess the effects of site design on building space conditioning energy use. An important strategy being investigated is the use of vegetation for shading, wind control, and temperature modification. The study described in this report has been conducted concurrently with a closely related research project at the Northeastern Forest Experiment Station of the USDA Forest Service in Pennsylvania (Heisler 1990). The objective of that project was to measure wind-speed reductions and solar obstructions caused by trees around representative houses within typical neighborhoods and to develop an empirical model for estimating these effects based on the physical characteristics of different neighborhoods. The objective of this work is to combine the results of the on-site microclimate measurements from the Heisler study with work in building energy simulation to calculate the energy impacts of the observed microclimatic changes due to trees.
Hull, R. Bruce. 1992. "How the Public Values Urban Forests." Journal of Arboriculture 18(2): March 1992.
Abstract: Results of this study confirm the intensity with which people value urban forests. Following Hurricane Hugo, residents of Charleston, South Carolina were interviewed and over 30% identified urban forests as being the most significant feature that was damaged. Results also indicate the numerous and diverse values associated with the urban forest: positive emotions evoked by the urban forests (11.6%), contribution to community image and aesthetics (9.5%), energy conservation (6.4%). personal values and memories (5%), environmental quality (3.4%), opportunities for leisure activities (2.3%) and functional concerns (1%). Trees symbolize spiritual values, personal memories, reminders of the past, preservation and endurance. All these symbols are highly valued by the public.
Hutchison, B.A., Taylor, F.G., Panel, T.G.R. 1983. Energy Conservation Mechanisms and Potentials of Landscape Design to Ameliorate Building Microclimates. Landscape Journal, 2(1), 19-39.
Abstract: An assessment of the space-conditioning energy conservation potentials of landscapes designed to ameliorate building microclimates is made. The physical bases for vegetative modifications of climate are discussed, and results of past studies concerning the effects of vegetation on space-conditioning energy consumption in buildings are reviewed. The state-of-the-art of energy-conserving landscape designs is assessed and recommendations for further research are presented.
Jensen, R.R., Boulton, J.R., Harper, B.T. 2003. The Relationship between Urban Leaf Area and Household Energy Usage in Terre Haute, Indiana, U.S. Journal of Arboriculture, 29(4), 226-230.
Abstract: The accrual of urban forest amenities and the estimation of these benefits is an essential step in the process of preserving and expanding urban forest resources. The purpose of this paper is to demonstrate that these benefits, specifically decreased cooling costs, can be effectively estimated using a mixed methodological approach that combines remotes sensing technologies with standard statistical analysis. This study tests the relationship between urban forest leaf area index (LAI) and household energy usage in summer 2001 in a mid-sized city. Results indicate an inverse relationship between LAI and energy usage, signifying that as LAI increases, energy usage decreases. This study could be used by urban planners and others to promote urban forests, justify urban forest projects, and assess the outcomes current policy.
Ko, Y. 2013. Urban Form and Residential Energy Use: A Review of Design Principles and Research Findings. Journal of Planning Literature, 28(4), 327-351.
Abstract: The effect of urban form on residential energy use has attracted much research, but it may be difficult to grasp the conclusions of that research because of inconsistencies in scope and methods employed. This article reviews the literature on how urban form affects residential energy use, particularly energy for space-conditioning (heating and cooling). Climate-responsive design principles are examined first and linked to research on how several factors affect residential energy use: housing type, density (physical compactness and dwelling unit density), community layout (street orientation and building configuration), and planting and other surface coverage. The research on each of these factors is summarized under three categories: experiments, simulation modeling, and statistical analysis of empirical data. Finally, implications for future research are discussed and suggestions for planning are made.
Kollin, C. A., M. Beaudouin, J. McBride, R. Roundtree. 1991. "On Balance: Weighing the Benefits and Costs of Urban Trees." A collaborative project of U.S. Forest Service Northeastern Forest Experiment Station, University of California, Berkeley, City of San Jose and San Jose Beautiful. 21 pp. City of San Jose, California 95133-1034.
Abstract: Trees have made a dramatic impact on our cities; they provide shade, produce oxygen, soften the hard urban edges. provide wildlife habitat, connect us with our natural environment, and offer the ephemeral qualities of seasonal change and beauty. Although these qualities are valued, it is often difficult to justify trees and their care in the face of shrinking public budgets. However, the recognition of global warming and of urban heat islands has added a new value to urban trees. One that, on balance, can provide enough environmental and economic benefits to tip the cost/benefit scale that justifies their net worth.
Laband, D.N., Sophocleus, J.P. 2009. An Experimental Analysis of the Impact of Tree Shade on Electricity Consumption. Arboriculture & Urban Forestry, 35(4), 197-202.
Abstract: The article presents a study which analyzes the impact of tree shade on electricity consumption in the U.S. The study was administered by comparing the electricity consumption of two identical buildings with the same temperature and located in different shade conditions using regression model. Trees cast shade on homes and buildings, lowering the inside temperatures and thus reducing the demand for power to cool these buildings during hot times of the year. The potential monetary savings may be sizable, especially for those who live in hot climates, because electricity usage for cooling residential and commercial structures in summer months is costly. The study examined electricity consumption used to run air conditioning units set at identical temperatures in two otherwise identical buildings, one set in full sun, the other in full shade during the summer months of 2008 in Beauregard, Alabama. The building in full sun required 2.6 times more electricity for cooling than the building in full shade. The findings contribute to a growing body of research which demonstrates that owners of residential and commercial properties located in hot regions can reap sizable monetary savings from shade trees that serve as natural complements to their artificial air-conditioning.
Laverne, R.J., Lewis, G.M. 1996. The Effect of Vegetation on Residential Energy use in Ann Arbor, Michigan. Journal of Arboriculture, 22(5), 234-243.
Abstract: Computer models have shown that proper placement of trees around climate- controlled buildings can significantly contribute to energy conservation by lowering cooling requirements in summer months and heating requirements in the winter. A study conducted in a residential neighborhood of Ann Arbor, Michigan, uses electric and natural gas utility company records to examine energy demand for homes in 3 areas with distinctly different levels of tree stocking. Field measurements quantify the density of vegetation that casts shade directly on homes, and aerial photo interpretation is used to evaluate potential wind shielding offered to individual homes by vegetation and adjacent buildings. Statistical analysis of data indicates that variability of structures, including different levels of insulation, infiltration, and efficiencies of space-conditioning appliances mask the effects of vegetation on energy use. Analysis is further complicated by a wide range of energy use habits of individual homeowners. However, trends are observed that suggest proper placement of trees with regard to seasonal solar gain and wind patterns may yield substantial savings of energy. Improper placement of trees may yield a significant increase in net levels of energy used for space conditioning.
Lorenzo, A.B., Blanche, C.A., Qi, Y.D., Guidry, M.M. 2000. Assessing residents' willingness to pay to preserve the community urban forest: a small-city case study. Journal of Arboriculture, 26(6), 319-325.
Abstract: Residents' willingness to pay for community urban forest preservation was assessed using a survey questionnaire mailed to 3009 households in the city of Mandeville, a suburb of New Orleans, Louisiana, USA. Survey responses indicated the following: (1) residents' willingness to pay for urban forest protection and preservation is positively associated with their perceptions of the benefits of trees but negatively associated with their perceptions of the annoying features of trees; (2) the willingness to pay a higher premium ($12) for tree preservation and protection is directly related to income levels; (3) more female than male respondents are willing to pay $6 to $12 per year for tree preservation but more male than female respondents are willing to pay more than $12 per year for tree preservation; (4) age, level of education, and type of residential ownership are not significantly associated with willingness to pay for tree preservation and protection; (5) more than 80% of respondents view the protection and preservation of urban trees as very important functions of the city and are willing to pay additional taxes for tree protection and preservation; and (6) more than 88% of respondents rate the city's overall performance in tree protection and maintenance as good to excellent. The survey results may find utility in crafting more effective support programs for urban tree protection and preservation.
Luly, C. J. A., Inc.) (996). "Final Analysis and Recommendations: Feasibility Study of Urban Forest's Economic Value (Part 1: Air Pollution Reduction Credits, Part 2: Carbon Credits or Offsets." Feasibility Study of the Urban Forest's Economic Value: Air Pollution Emission Reduction Credits. Presented by ACRT, Inc. (July 25, 1996) to National Urban and Community Forestry Advisory Council (NUCFAC).
Abstract: An investigation of the feasibility of funding urban forest management through the sale of air pollution emission-reduction credits (F.RCs). ERCs are created when an air pollution source, such as a utility company or industrial factory, reduces its pollution emission more than is required by regulation. The specific legislative, regulatory and market factors affecting creation of urban forestry ERCs are discussed in detail. Despite existence of these key elements, urban forestry ERCs are not feasible based on the findings of this investigation and the recommendation of the scientific review committee. Ozone was identified as the air pollutant most likely to be included in an air quality improvement program. Quantification of the removal or air pollutants by the urban forest is one of the most important issues limiting ERC program development. For urban forestry ERCs to be considered in the future, the EPA will require evidence that their mandated air quality goals will not be compromised. More importantly, the EPA will not jeopardize the environmental and health issues it is charged with protecting without sufficient evidence that urban forestry ERCs are real and verifiable.
Marotz, G.A., Coiner, J.C. 1973. Acquisition and Characterization of Surface Material Data for Urban Climatological Studies. Journal of Applied Meteorology and Climatology, 12, 919-923.
Abstract: A sampling and analysis scheme is presented and briefly illustrated for examination of the type, amount and degree of areas contiguity among surface materials in urban areas. Such data are necessary if we are to understand and model the spatial and temporal effects of urban places on atmospheric variables. Medium-scale aerial photographs are used as the data source; surface material information is extracted using a systematic grid-cell routine. Percent coverage values are computed and a linkage technique is used to compare areal contiguity of materials within and among five selected eastern Kansas cities. Results suggest that 1) the amount of vegetated surface within a city has been grossly underestimated, 2) materials tend to aggregate by types in essentially bimodal fashion, 3) materials within each modal category change with city size, and 4) geographic location affects the nature of the surface material matrix.
Mattingly, G.E., Peters, E.F. 1977. Wind and Trees: Air Infiltration Effects on Energy in Housing. Journal of Wind Engineering and Industrial Aerodynamics, 2(1), 1-19.
Abstract: A series of wind tunnel tests have been conducted to examine the ways in which wind influences air infiltration energy losses in residential housing. A quantitative model for air infiltration has been developed that is based upon a linear relationship between air flow and pressure difference across walls and roof surfaces. With the model, a variety of windhouse orientations are tested, and the sheltering effects provided by solid fences, adjacent houses, and tall evergreen trees are assessed and compared.
McHale, M.R., McPherson, E.G., Burke, I.C. 2007. The potential of urban tree plantings to be cost effective in carbon credit markets. Urban Forestry & Urban Greening, 6(1), 49-60.
Abstract: Emission trading is considered to be an economically sensitive method for reducing the concentrations of greenhouse gases, particularly carbon dioxide, in the atmosphere. There has been debate about the viability of using urban tree plantings in these markets. The main concern is whether or not urban planting projects can be cost effective options for investors. We compared the cost efficiency of four case studies located in Colorado, and used a model sensitivity analysis to determine what variables most influence cost effectiveness. We believe that some urban tree planting projects in specific locations may be cost effective investments. Our modelling results suggest that carbon assimilation rate, which is mainly a function of growing season length, has the largest influence on cost effectiveness, however resource managers can create more effective projects by minimizing costs, planting large-stature trees, and manipulating a host of other variables that affect energy usage.
McPherson, E.G., Stilgoe, J.R., Herrington, L.P., Zanetto, J., Thayer, R.L., Heisler, G.M., Pitt, D.G., Hrabak, R., Socwell, D., Morris, D. 1984. Energy-Conserving Site Design. American Society of Landscape Architects, Washington, DC.
Abstract: Papers by 11 contributors of different backgrounds emphasize the importance of an interdisciplinary approach in guiding landscape architects, architects, planners, developers, students, and the lay public toward energy-efficient site planning and design. The papers are grouped into four major sections: Overview, Analysis and Planning, Landscape Design, and Alternative Futures. Three appendices present material on modifications to the planning process, data and tools for analyzing climate, and precision planting for solar control and solar access. A separate abstract was prepared for 14 chapters selected for the Energy Data Base and Energy Abstracts for Policy Analysis.
McPherson, E.G., Herrington, L.P., Heisler, G.M. 1988. Impacts of Vegetation on Residential Heating and Cooling. Energy and Buildings, 12(1), 41-51.
Abstract: Computer simulation has been used to test the effects of irradiance and wind reductions on the energy performance of similar residences of 143 m2 in four U.S. cities — Madison, Salt Lake City, Tucson and Miami — representing four different climates. Irradiance reductions from vegetation were modeled using SPS, which simulates shade cast from plants on buildings, and MICROPAS, a microcomputer-based energy analysis program. Space cooling costs were found to be most sensitive to roof and west wall shading, whereas heating costs were most sensitive to south and east wall shading. Irradiance reductions were shown to substantially increase annual heating costs in cold climates ($128 or 28% in Madison), and reduce cooling costs in hot climates ($249 or 61% in Miami). Dense shade on all surfaces reduced peak cooling loads by 31% – 49% or 3108 – 4086 W. A 50% wind reduction was shown to lower annual heating costs by $63 (11%) in Madison, and increased annual cooling costs by $68 (15%) in Miami. Planting designs for cold climates should reduce winter winds and provide solar access to south and east walls. This guideline also applies for temperate climates, however it is also important to avoid blocking summer winds. In hot climates, high-branching shade trees and low ground covers should be used to promote both shade and wind.
McPherson, E.G., Simpson, J.R., Livingston, M. 1989. Effects of Three Landscape Treatments on Residential Energy and Water Use in Tucson, Arizona. Energy and Buildings, 13(2), 127-138.
Abstract: Vegetation can reduce the cooling loads of buildings in hot arid climates by modifying air temperature, solar heat gain, longwave heat gain, and heat loss by convection. However, savings from reduced mechanical cooling may be offset by increased irrigation water costs. In this study, three similar "1/4 - scale" source model buildings were constructed and surrounded with different landscapes: turf, rock mulch with a foundation planting of shrubs, and rock mulch with no plants. Irrigation water use and electricity required to power the three room-sized air conditioners and interior lights were measured for two approximately week-long periods. Electrical energy consumed for air-conditioning by the rock model was 20 – 30% more than for the turf and shade models. Factors accounting for these differences in energy performance include dense shade that substantially reduced solar heat gain for the shaded model, a 16% difference in long wave radiation flux between the rock and turf treatments, and a maximum drybulb depression of 4 °C over the turf compared with the rock. Air-conditioning savings exceeded water costs for shade treatments that were simulated to receive moderate and low amounts of irrigation water. These preliminary findings suggest that the localized effects of vegetation on building microclimate may be more significant than boundary layer effects in hot arid regions.
McPherson, E.G., Rowntree, R.A. 1993. Energy conservation potential of urban tree planting. Journal of Arboriculture, 19(6), 321-331.
Abstract: Findings from monitoring and computer simulation studies are reviewed which indicate that trees can be a cost-effective energy conservation measure for some electric utilities. Simulations reported here suggest that a single 25-ft tall tree can reduce annual heating and cooling costs of a typical residence by 8 to 12% ($10-25). Assuming annual savings of $10 per household, a nationwide (US) residential tree planting program could eventually save about $1 billion each year. A study of the potential for energy-conserving shade tree plantings within residential sections of San Diego, California, found that over 40% of all houses surveyed had space available for a tree opposite their west wall. The 30-year net present value of proposed shade tree plantings for demand side management in Fresno, California, was projected to be $22.3 million, with an overall benefit/cost ratio of 19. The largest benefits were attributed to property value enhancement, energy savings, storm water runoff avoided and atmospheric carbon removal, while greatest projected costs were from pruning, planting and program administration.
McPherson, E.G. 1993. Evaluating the Cost Effectiveness of Shade Trees for Demand-Side Management. The Electricity Journal, 6(9), 57-65.
Abstract: Proper planning and placement of trees as part of a utility DSM strategy offers a number of benefits to utilities and their customers in certain markets. When all of the benefits — including those not easily quantified — are counted, trees may be a resource and customer service tool your utility should consider.
McPherson, E.G., Nowak, D.J., Rowntree, R.A. 1994. Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. Radnor, PA. General technical report NE-186.
Abstract: Results of the 3-year Chicago Urban Forest Climate Project indicate that there are an estimated 50.8 million trees in the Chicago area of Cook and DuPage Counties; 66 percent of these trees rated in good or excellent condition. During 1991, trees in the Chicago area removed an estimated 6,145 tons of air pollutants, providing air cleansing valued at $9.2 million dollars, these trees also sequester approximately 155,000 tons of carbon per year, and provide residential heating and cooling energy savings that, in turn, reduce carbon emissions from power plants by about 12,600 tons annually. Shade, lower summer air temperatures, and a reduction in windspeed associated with increasing tree cover by 10 percent can lower total heating and cooling energy use by 5 to 10 percent annually ($50 to $90 per dwelling unit). The projected net present value of investment in planting and care of 95,000 trees in Chicago is $38 million ($402 per planted tree), indicating that the long-term benefits of trees are more than twice their costs. Policy and program opportunities to strengthen the connection between city residents and city trees are presented.
McPherson, E.G. 1994. Energy-saving potential of trees in Chicago. Chp 7 in Chicago's Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate Project. US Forest Service, General technical report NE-186, 95-113.
Abstract: Parametric computer simulations of microclimates and building energy performance were used to investigate the potential of shade trees to save residential heating and cooling energy use in the City of Chicago. Prototypical buildings included one-, two-, and three-story brick buildings similar to residences in the Chicago area, and one-and two-story wood-frame buildings representing suburban construction. To validate the energy performance of prototypes, building performance indices of reference buildings were calculated.in some cases using whole-house metered data and compared with indices of the prototypes. Increasing tree cover by 10 percent (corresponding to about three trees per building) could reduce total heating and cooling energy use by 5 to 10 percent ($50 to $90). On a per-tree basis, annual heating energy can be reduced by about 1.3 percent ($10, 2 M Btu),cooling energy by about 7 percent ($15. 125 kilowatt-hours),and peak cooling demand by about 6 percent (0.3 kilowatts).Simulation results were used in a 20-year economic analysis of costs and benefits associated with a hypothetical shade-tree program. Benefit-cost ratios of 1.35 for trees planted around typical two-story residential buildings and 1.90 for trees near energy-efficient wood-frame buildings indicate that a utility-sponsored shade-tree program could be cost-effective for both existing and new construction in Chicago.
McPherson, E. G., E. G. McPherson, D.J. Nowack, and R.A. Roundtree. 1994. Benefits and Costs of Tree Planting and Care in Chicago. Radnor, PA, USDA Forest Service. Gen. Tech. Rep. NE-186: 114-132.
Abstract: Benefit-cost analysis is used to estimate the net present value, benefit-cost ratio, and discounted payback periods of proposed tree plantings in the City of Chicago. A typical 'tree species, green ash (Fraxinus pennsylvanica), was located in 'typical" park, residential yard, street, highway, and public housing sites. The 30-year stream of annual costs and benefits associated with planting 95,000 trees was estimated using a computer model called Cost-Benefit Analysis of Trees(C-BAT) and discount rates of 4, 7, and 10 percent. NPV were positive and projected benefit-cost ratios were greater than 1 at all discount rates. Assuming a 7-percent discount rate, a net present value of $38 million or $402 per planted tree was projected. Benefit-cost ratios were largest for trees planted in residential yard and public housing sites (3.5), and least for park (2.1) and highway (2.3) sites. Discounted payback ranged from 9 to 15 years. Expenditures for planting alone accounted for more than 80 percent of projected costs except at public housing sites, while the largest benefits were attributed to "other" benefits (e.g., scenic, wildlife, improved water quality, noise abatement, and social values) and energy savings. Considerations for planting and managing Chicago's urban forest to maximize return on investment are presented.
McPherson, E. G. and J. R. Simpson 1995. Shade Trees as a Demand-side Resource. Home Energy. Berkeley, CA, the Home Energy Magazine. 12: 11-17.
Abstract: Shade tree programs offer opportunities for utilities to take civic leadership roles with respect to environmental issues, conservation education, neighborhood revitalization and job training. Trees can increase of decrease energy used for buildings. Large parks or residential neighborhoods with extensive vegetation can produce air temperature reductions as great as 10 degrees F compared to nearby areas with little vegetation. At this scale, large trees increase the aerodynamic roughness of the urban canopy layer, thereby reducing wind speeds by as much as 50%. The paper discusses relations between cooling savings, climate and building insulation level and gives examples from various landscape settings. The authors conclude that shade trees that are carefully selected, located and maintained can be cost-effective energy conservation measures but caution that benefits are highly site-specific.
McPherson, E.G., Nowak, D., Heisler, G., Grimmond, S., Souch, C., Grant, R., Rowntree, R. 1997. Quantifying Urban Forest Structure, Function, and Value: the Chicago Urban Forest Climate Project. Urban Ecosystems, 1(1), 49-61.
Abstract: This paper is a review of research in Chicago that linked analyses of vegetation structure with forest functions and values. During 1991, the regions trees removed an estimated 5575 metric tons of air pollutants, providing air cleansing worth 9.2 million. Each year they sequester an estimated 315 800 metric tons of carbon. Increasing tree cover 10% or planting about three trees per building lot saves annual heating and cooling costs by an estimated 50 to 90 per dwelling unit because of increased shade, lower summertime air temperatures, and reduced neighborhood wind speeds once the trees mature. The net present value of the services trees provide is estimated as 402 per planted tree. The present value of long-term benefits is more than twice the present value of costs.
McPherson, E.G. 2001. Sacramento's Parking Lot Shading Ordinance: Environmental and Economic Costs of Compliance. Landscape and Urban Planning, 57(2), 105-123.
Abstract: A survey of 15 Sacramento parking lots and computer modeling were used to evaluate parking capacity and compliance with the 1983 ordinance requiring 50% shade of paved areas (PA) 15 years after development. There were 6% more parking spaces than required by ordinance, and 36% were vacant during peak use periods. Current shade was 14% with 44% of this amount provided by covered parking. Shade was projected to increase to 27% (95% CI 24–37%) when all lots in the sample were 15-year-old. Annual benefits associated with the corresponding level of tree shade were estimated to be US $ 1.8 million (CI US$ 1.5–2.6 million) annually citywide, or US $ 2.2 million less than benefits from 50% shade (CI US$ 1.4–2.5 million). The cost of replacing dying trees and addressing other health issues was US $ 1.1 million. Planting 116,000 trees needed to achieve 50% shade was estimated to cost approximately US $ 20 million. Strategies for revising parking ordinances to enhance their effectiveness are presented.
McPherson, E.G., Simpson, J.R. 2003. Potential Energy Savings in Buildings by an Urban Tree Planting Program in California. Urban Forestry & Urban Greening, 2(2), 73-86.
Abstract: Tree canopy cover data from aerial photographs and building energy simulations were applied to estimate energy savings from existing trees and new plantings in California. There are approximately 177.3 million energy-conserving trees in California communities and 241.6 million empty planting sites. Existing trees are projected to reduce annual air conditioning energy use by 2.5% with a wholesale value of $ 485.8 million. Peak load reduction by existing trees saves utilities 10% valued at approximately $778.5 million annually, or $ 4.39/tree. Planting 50 million trees to shade east and west walls of residential buildings is projected to reduce cooling by 1.1% and peak load demand by 4.5% over a 15-year period. The present wholesale value of annual cooling reductions for the 15-year period is $ 3.6 billion ($ 71/tree planted). Assuming total planting and stewardship costs of $ 2.5 billion ($ 50/tree), the cost of peak load reduction is $ 63/kW, considerably less than the $ 150/kW benchmark for cost-effectiveness. Influences of tree location near buildings and regional climate differences on potential energy savings are discussed.
McPherson, E.G., Muchnick, J. 2005. Effects of Street Tree Shade on Asphalt Concrete Pavement Performance. Journal of Arboriculture, 31(6), 303-310.
Abstract: Forty-eight street segments were paired into 24 high and low-shade pairs in Modesto, California, U.S. Field data were collected to calculate a Pavement Condition Index (PCI) and Tree Shade Index (TSI) for each segment. Statistical analyses found that greater PCI was associated with greater TSI, indicating that tree shade was partially responsible for reduced pavement fatigue cracking, rutting, shoving, and other distress. Using observed relations between PCI and TSI, an unshaded street segment required 6 slurry seals over 30 years, while an identical one planted with 12 crape myrtles (Lagerstroemia indica, 4.4 m [14 ft] crown diameter) required 5 slurry seals, and one with 6 Chinese hackberry (Celtis sinensis, 13.7 m [45 ft] crown diameter) required 2.5 slurry seals. Shade from the large hackberries was projected to save $7.13/m2 ($0.66/ft2) over the 30-year period compared to the unshaded street.
Mehta, M. 2009. Water Efficiency Saves Energy: Reducing Global Warming Pollution through Water Use Strategies. N.R.D.Council: Water Facts. 4. www.nrdc.org/policy March 2009.
Abstract: The collection, distribution, and treatment of drinking water and wastewater nationwide consume tremendous amounts of energy and release approximately 116 billion pounds of carbon dioxide (CO2) per year—as much global warming pollution each year as 10 million cars.1 The energy water connection is particularly strong in the driest regions of the United States, such as the Southwest, where significant amounts of energy are used to import water. Solutions exist to cut both water and energy use. Through water efficiency measures, we can help to protect dry areas from drought, lower consumers’ utility bills, and reduce global warming pollution.
Moffat, A. S. and M. Schiler. 1981. Landscape Design that Saves Energy. New York, NY, William Morrow and Company, Inc.
Abstract: This book shows homeowners how the selection and placement of trees, plants, pools, and other landscaping features can significantly reduce energy costs for heating and cooling. The text describes many species, reviews landscape principles and covers things from windbreaks to hardiness zones.
Moffat, A. S., et al. (1994). Energy-efficient and Environmental Landscaping: Cut Your Utility Bills by up to 30 Percent and Create a Natural, Healthy Yard. South Newfane, VT, Appropriate Solution Press.
Abstract: Cut Your Utility Bills by up to 30 Percent and Create a Natural, Healthy Yard. The strategy for handling the sun is simple: block it when it's hot, let it in when it's cold. Energy efficient landscaping can substantially reduce a home's utility bills. By how much? Between $300 and $750 a year according to studies, and that doesn't even include the increased value that low utility bills and a well-designed landscape add to home resale prices.
Nikoofard, S., Ugursal, V.I., Beausoleil-Morrison, I. 2011. Effect of External Shading on Household Energy Requirement for Heating and Cooling in Canada. Energy and Buildings, 43(7), 1627-1635.
Abstract: Shading by neighboring buildings and trees impacts the energy requirement of a building by reducing the amount of radiant energy absorbed and stored by its thermal mass. This study intends to quantify the magnitude of the effect of site shading on the energy requirement of residential buildings in Canada using a representative two-story detached house. Site shading effects of neighboring buildings and trees on annual heating and cooling energy requirements are evaluated using a building energy simulation program. The effects of the orientation, distance and size of the neighboring object on heating and cooling energy requirement are investigated for four major cities (Halifax, Toronto, Calgary, Vancouver) representing the major climatic regions in Canada (Atlantic, Central, Prairies, Pacific). It is found that the annual heating and cooling energy requirement of a house in Canada may be affected by as much as 10% and 90%, respectively, by the existence as well as the orientation, size and distance of a neighboring obstruction. Therefore, it is recommended that in building energy simulation studies, external shading should be given due consideration.
Nowak, David J., Mary H. Noble, Susan M. Sisinni, and John F. Dwyer. 2001. Assessing the US Urban Forest Resource. Journal of Forestry March(2001): 37-42.
Abstract: Urban areas in the conterminous United States doubled in size between 1969 and 1994, and currently cover 3.5 percent of the total land area and contain more than 75 percent of the US population. Urban areas contain approximately 3.8 billion trees with an average tree canopy cover of 27 percent. The extent and variation of urban forests across the 48 states are explored to help build a better understanding of this significant national resource. Urbanization and urban forests are likely to be a significant focus of forestry in the 21st century.
Nowak, D.J., Crane, D.E. 2002. Carbon storage and sequestration by urban trees in the USA. Environmental Pollution, 116(3), 381-389.
Abstract: Based on field data from 10 USA cities and national urban tree cover data, it is estimated that urban trees in the coterminous USA currently store 700 million tons of carbon ($14 300 million value) with a gross carbon sequestration rate of 22.8 million t C/year ($460 million/year). Carbon storage within cities ranges from 1.2 million t C in New York City, New York, to 19 300 t C in Jersey City, New Jersey. Regions with the greatest proportion of urban land are the northeast (8.5%) and the southeast (7.1%). Urban forests in the north central, northeast, south central and southeast regions of the USA store and sequester the most carbon, with average carbon storage per hectare greatest in southeast, north central, northeast and Pacific northwest regions, respectively. The national average urban forest carbon storage density is 25.1 t C/ha, compared with 53.5 t C/ha in forest stands. These data can be used to help assess the actual and potential role of urban forests in reducing atmospheric carbon dioxide, a dominant greenhouse gas.
Nowak, D.J. 2006. Institutionalizing urban forestry as a "biotechnology" to improve environmental quality. Urban Forestry & Urban Greening, 5(2), 93-100.
Abstract: Urban forests can provide multiple environmental benefits. As urban areas expand, the role of urban vegetation in improving environmental quality will increase in importance. Quantification of these benefits has revealed that urban forests can significantly improve air quality. As a result, national air quality regulations are now willing to potentially credit tree planting as means to improve air quality. Similarly, quantification of other environmental benefits of urban trees (e.g., water quality improvement, carbon sequestration) could provide for urban vegetation to be incorporated in other programs/regulations designed to improve environmental quality.
Nowak, D.J. and E.J. Greenfield. 2012. Tree and impervious cover change in U.S. cities. Urban Forestry & Urban Greening 11 (2012) 21–30.
Abstract: Paired aerial photographs were interpreted to assess recent changes in tree, impervious and other cover types in 20 U.S. cities as well as urban land within the conterminous United States. National results indicate that tree cover in urban areas of the United States is on the decline at a rate of about 7900 ha/yr or 4.0 million trees per year. Tree cover in 17 of the 20 analyzed cities had statistically significant declines in tree cover, while 16 cities had statistically significant increases in impervious cover. Only one city (Syracuse, NY) had a statistically significant increase in tree cover. City tree cover was reduced, on average, by about 0.27 percent/yr, while impervious surfaces increased at an average rate of about 0.31 percent/yr. As tree cover provides a simple means to assess the magnitude of the overall urban forest resource, monitoring of tree cover changes is important to understand how tree cover and various environmental benefits derived from the trees may be changing. Photo-interpretation of digital aerial images can provide a simple and timely means to assess urban tree cover change to help cities monitor progress in sustaining desired urban tree cover levels.
Pandit, R., and Laband, D.N. 2010. Energy Savings from Tree Shade. Ecological Economics, 69(6), 1324-1329.
Abstract: Trees cast shade on homes and buildings, lowering the inside temperatures and thus reducing demand for power to cool these buildings during hot times of the year. Drawing from a large sample of residences in Auburn, Alabama, we develop a statistical model that produces specific estimates of the electricity savings generated by shade-producing trees in a suburban environment. This empirical model links residential energy consumption during peak summer (winter) months to average energy consumption during non-summer/non-winter months, behaviors of the occupants, and the extent, density, and timing of shade cast on the structures. Our estimates reveal that tree shade generally is associated with reduced (increased) electricity consumption in the summertime (wintertime). In summertime, energy savings are maximized by having dense shade. In wintertime, energy consumption increases as shade percentage in the morning, when outdoor temperatures are at their lowest, increases.
Pandit, R., and Laband, D.N. 2010. A Hedonic Analysis of the Impact of Tree Shade on Summertime Residential Energy Consumption. Arboriculture & Urban Forestry, 36(2), 73-80.
Abstract: Trees cast shade on homes and buildings, lowering the inside temperatures and thus reducing the demand for power to cool these buildings during hot times of the year. Drawing from a large sample of residences in Auburn, Alabama, U.S., a statistical model was developed to produce specific estimates of the electricity savings generated by shade-producing trees in a suburban environment. This empirical model links residential energy consumption to hedonic characteristics of the structures, characteristics/behaviors of the occupants, and the extent and density of shade cast on the structures at different times of the day.
Parker, J.H. 1983. Landscaping to Reduce the Energy Used in Cooling Buildings. Journal of Forestry, 81(2), 82-105.
Abstract: Although much less energy is expended in the United States for space cooling than for space heating, this end use is significant in many areas of the country and is often the major factor in utility peak electrical demands during the warmer months. Vegetative landscaping can reduce the energy required to cool residences by providing shade and wind control and through microclimate cooling via evapotranspiration. "Precision landscaping" design concepts can optimize the energy savings, particularly during utility peak demand periods. Energy analyses of an insulated mobile home show that landscaping can reduce cooling energy by more than 50 percent during warm summer days. Deciduous trees are particularly useful because they allow solar radiation to reach a building during the heating season.
Parker, J.H. 1987. The Use of Shrubs in Energy Conservation Plantings. Landscape Journal, 6(2), 132-139.
Abstract: Although most energy conservation landscape analyses emphasize the use of trees, this study has analyzed the use of shrubs to reduce cooling requirements of buildings in warm-humid climates. Reductions in temperatures of walls of concrete-block houses as a result of shrubs being planted immediately adjacent to the walls have been determined for warm summer days. During periods of direct sunlight, temperatures of walls shaded by shrubs were 24 to 29°F cooler than uncovered walls. Shrub-shaded walls were significantly cooler even during periods of no direct solar radiation. Shrubs located immediately adjacent to walls were also effective in reducing prevailing summer winds impacting on a building by 75 to 93%. These experimental results have been used to develop some specific landscape design strategies which use shrubs to reduce residential air conditioning.
Rosenfeld, A.H., Akbari, H., Romm, J.J., Pomerantz, M. 1998. Cool Communities: Strategies for Heat Island Mitigation and Smog Reduction. Energy and Buildings, 28(1), 51-62.
Abstract: Adopting our 'cool communities' strategies of reroofing and repaying in lighter colors and planting shade trees can effect substantial energy savings, directly and indirectly. In our target city of Los Angeles, annual residential air-conditioning (A/C) bills can be reduced directly by about US$100 M and, because these strategies serve to cool the air in the Los Angeles basin and reduce smog exceedance levels by about 10%, an additional savings of US$70 M in indirect cooling and US $360 M in smog-reduction benefits - a total savings of about US$1/2 B per year - is possible. Trees are most effective if they shade buildings, but the savings are significant even if they merely cool the air by evapotranspiration. In Los Angeles, avoided peak power for air conditioning can reach about 1.5 GW (more than 15% of the city's air conditioning). Generalized to the entire US, we estimate that 25 GW can be avoided with potential annual benefits of about US$5 B by the year 2015. Recent steps taken by cities in the warm half of US towards adoption of cool communities include (1) incorporation of cool roofs in the revised ASHRAE building standards S90.1 and (2) inclusion of cool surfaces and shade trees as tradable smog-offset credits in Los Angeles. Other step underway include (1) plans by the US Environmental Protection Agency (EPA) to approve heat island mitigation measures in the state implementation plan to comply with ozone standards and (2) plans for ratings and labeling of cool surfaces.
Rosenzweig, C., Solecki, W.D. 2001. Climate Change and a Global City: Learning from New York. Environment, 43(3), 8-18.
Abstract: Rosenzweig and Solecki present a case study of metropolitan New York--supported by data from the Metropolitan East Coast Regional Assessment--that analyzes the multidimensional and interactive effects of climate change on megacities. The complex nature of these impacts promises to challenge urban environmental managers worldwide.
Rosenzweig, C., Solecki, W., Parshall, L., Gaffin, S., Lynn, B., Goldberg, R., Cox, J., Hodges, S. 2006. Mitigating New York City’s Heat Island with Urban Forestry, Living Roofs, and Light Surfaces. Am. Meterolo. Soc. J3.2. 5pp.
Abstract: New York City, like other large cities, is warmer than surrounding areas due to the urban heat island effect, which is defined as an increase in urban air temperature as compared to surrounding suburban and rural temperature. The development of a heat island has regional-scale impacts on energy demand, air quality, and public health. Heat island mitigation strategies, such as urban forestry, living/green roofs, and light surfaces, could be implemented at the community level within New York City, but their effects need to be tested with comparable methodologies. This study uses a regional climate model (MM5) in combination with observed meteorological, satellite, and GIS data to determine the impact of each of the mitigation strategies on surface and near-surface air temperature in the New York Metropolitan Region over space and time. The effects of localized changes in land surface cover in six case study areas are evaluated in the context of regional atmospheric mixing.
Rosenzweig, Cynthia, Solecki, Wm. D.; Parshall, Lily; Lynn, Barry; Cox, Jennifer; Goldberg, R; Hodges, S; Gaffin, S; Slosberg, R. B.; Savio, P.; Dunstan, F.; Watson, M. 2009. Mitigating New York City's Heat Island. Bulletin of the American Meteorological Society 90(9): 16.
Abstract: The article presents information on the New York City's heat island mitigation strategies to improve urban vegetation and its plans to increase the ratio of impervious surfaces. It informs about the benefits gained by heat island mitigation and the collaboration between researchers and stakeholders and their interdisciplinary methods and neighborhood-scale strategies that account for common priorities and constraints. The researchers concluded that maximizing the amount of vegetation in the city with tree planting and green roofs is the most effective way to reduce urban air temperature.
Rudie, R.J., Dewers, R.S. 1984. Effects of Tree Shade on Home Cooling Requirements. Journal of Arboriculture, 12, 320-322.
Abstract: This study was implemented to provide more information on the effects of shade trees on summer cooling energy reduction. A sample of 113 homes of similar setting and design in College Station, Texas was used. Electrical data reduced to kilowatt hours per square foot of living area were used as the dependent variable. Shade proved to be the most significant of several variables observed in reducing electrical energy usage.
Sacamano, Paul L., Leonard F. Burkhart, David M. Cole, Roger C. Funk, Stephen G. Holcomb, Trevor F. Vidic, Marianne L. Waindle. 1993. Consolidating and Communicating Urban Forest Benefits and Costs of Urban Forestry for Enhanced Technology Transfer in the Southern Region. Davey Resource Group, Irvine, California 92714.
Abstract: The booklet contains a literature review, urban forest benefit-cost computer program and a communications plan along with a bibliography. Beginning in the spring of 1993, technicians and urban forestry experts with Davey Resource Group conducted a comprehensive review of literature and pertinent information related to the benefits and costs of the urban forest. Information sources were searched for quantifiable data on tree functions. Benefits and costs initially identified were categorized into environmental and socioeconomic impacts. This review first considers the economic approaches used to monetize trees and environmental resources and follows with a survey of benefit and cost research that relates tree characteristics to quantifiable influences and occasionally monetizes these impacts.
Sailor, D.J. 1998. Simulations of Annual Degree Day Impacts of Urban Vegetative Augmentation. Atmospheric Environment, 32(1), 43-52.
Abstract: One approach for reducing summertime energy consumption in cities is through implementation of urban vegetation planting programs. While the direct effect of such programs is to cool individual buildings and air conditioning condenser units, there is also an indirect regional cooling associated with increasing vegetative cover. This paper models the regional cooling impacts of urban vegetation augmentation through a series of meteorological simulations. Numerical experiments were conducted for a hypothetical city located at various latitudes (25–45°N) and subjected to several background climate conditions. Simulations were conducted for one day from each month of the year to determine seasonal variability of the impacts of vegetation on urban climates. To provide a simple and useful index of the climatic impact of urban vegetation, cooling and heating degree days were calculated for each simulation. Comparison of baseline degree days for six modeled cities at various latitudes across the United States with the corresponding historical climate data indicate that the modeling approach was successful in reproducing the general temperature profile characteristics of each city.
Simulation results indicate that the regional climate can be significantly cooled through the planting of urban vegetation. For regions of low-to-moderate ambient humidity, increasing the vegetative fraction of the core of a hypothetical city by less than 0.065 resulted in an estimated 3–5% decrease in summertime cooling loads. It is believed that this effect could be doubled by application of a more ambitious program. This energy saving is due to the indirect regional cooling effects of vegetation, and does not include the direct energy savings associated with shading of individual buildings. The wintertime energy costs associated with vegetative augmentation were found to be smaller than the summertime savings, and may be negligible in the case of deciduous vegetation.
Sailor, D.J., Rainer, L., Akbari, H. 1992. Measured Impact of Neighborhood Tree Cover on Microclimate in: California Institute for Energy Efficiency (CIEE) Annual Conference, California Institute for Energy Efficiency (CIEE). San Diego, CA.
Abstract: In this paper we present results of our investigation into the relationship between urban microclimate and the local density of tree cover as measured in Sacramento, California. These results were obtained through analysis of data collected in a two-month long monitoring program with automatic weather stations installed at 15 residential locations throughout the city. Measured wind speeds showed a highly negative correlation with respect to tree cover. Daily peak air temperatures showed significant variation often differing from site to site by 2 to 4 degrees C (approximately 3.5 to 7 °F). A complex interaction between several competing factors is discussed leading to the conclusion that additional tree cover may actually increase urban air temperatures on synoptically cool days. It is suggested that this does not have a significant adverse effect in terms of overall summer urban cooling load. This is supported by an integrated analysis of the temperature data which yielded preliminary estimates indicating that residential cooling local (as measured by cooling degree days) may decrease by 5 to 10% per 10% increase in tree cover.
Sawka, M., Millward, A.A., McKay, J., Sarkovich, M. 2013. Growing Summer Energy Conservation through Residential Tree Planting. Landscape and Urban Planning, 113, 1-9.
Abstract: Energy conservation strategies are now at the forefront of electrical utility demand-side management planning. Residential shade trees extenuate the heating of buildings in the summertime by intercepting insolation and by evapotranspirative cooling of their immediate surroundings. By modifying location-specific climate data and tree growth characteristics, we adapt the Sacramento Municipal Utility District's (SMUD) Tree Benefits Estimator for application in Toronto, Canada. We then use our tool to model the air conditioning energy conservation savings delivered by 577 trees planted in Toronto backyards between 1997 and 2000. In urban residential neighborhoods, where houses are closely spaced, the energy conservation benefits of planting a tree depend on species, on pre-existing canopy, and on placement of the tree with respect to distance and orientation from buildings. Study trees contributed 77,140 kWh (167 kWh/tree) of electricity savings as of 2009, 54.4% of which was due to shading of neighboring houses. Twenty-five years following planting, we estimate that each study tree will have delivered, on average, between 435 and 483 kWh in energy conservation benefit. Our findings indicate that residential tree-planting program in densely settled urban areas should not focus exclusively on location-driven strategic planting to yield large energy conservation benefits. Instead, we argue that priority should be given to selecting planting locations that will maximize tree survival as neighborhood energy conservation benefits of a tree that achieves mature stature often outweigh the homeowner-specific benefits of a strategically planted tree.
Scott, K.I., Simpson, J.R., McPherson, E.G. 1999. Effects of Tree Cover on Parking Lot Microclimate and Vehicle Emissions. Journal of Arboriculture, 25(3), 129-142.
Abstract: A pilot study was performed to measure the difference in parking lot microclimate resulting from the presence or absence of shade tree cover. Microclimate data from contrasting shade regimes were then used as input to a motor-vehicle emissions model. Model results were used to estimate the potential for regional increases in parking lot tree cover to reduce motor-vehicle hydrocarbon and nitrogen oxide (NOx) emissions.
Scott, J.L. and Betters, D.R. 2000. Economic Analysis of Urban Tree Replacement Decisions. Journal of Arboriculture, 2000(26), 2.
Abstract: Urban forest managers often are required to make decisions about whether to retain or replace an existing tree. In part, this decision relies on an economic analysis of the benefits and costs of the alternatives. This paper presents an economic methodology that helps address the tree replacement problem. The procedures apply to analyzing the benefits and costs of existing trees as well as future replacement trees. A case study, involving a diseased American elm (Ulmus americana) is used to illustrate an application of the methodology. The procedures should prove useful in developing economic guides for tree replacement/retention decisions.
Simpson, J.R. and McPherson, E.G. 1996. Potential of Tree Shade for Reducing Residential Energy Use in California. Journal of Arboriculture, 22(1), 10-18.
Abstract: Electric utilities in California currently sponsor planting of approximately 75,000 yard trees annually as an energy conservation measure. In this study we evaluated the potential effects of tree shade on residential air conditioning and heating energy use for a range of tree orientations, building insulation levels and climate zones in California using computer simulation. Trees shading a home's west exposure produced the largest savings, both annual (kWh) and peak (kW), for all climate zones and insulation levels considered. Next largest savings were for southwest (annual and peak) and east (annual only) locations. Three trees (two on the west, one on the east side) reduced annual energy use for cooling 10 to 50 percent (200 to 600 kWh, $30 to $110) and peak electrical use up to 23 percent (0.7 kW). Except in climates with little air-conditioning demand, cooling load reductions were always greater than increased heating loads associated with shade from south side trees in winter. Air-conditioning savings, both peak and annual, were larger in warmer climates and uninsulated buildings; percentage savings were larger in cooler climates and for more energy efficient buildings. Recommendations are made regarding locating yard trees to maximize energy savings.
Simpson, J.R., McPherson, E.G. 1998. Simulation of Tree Shade Impacts on Residential Energy Use for Space Conditioning in Sacramento. Atmospheric Environment, 32(1), 69-74.
Abstract: Tree shade reduces summer air conditioning demand and increases winter heating load by intercepting solar energy that would otherwise heat the shaded structure. We evaluate the magnitude of these effects here for 254 residential properties participating in a utility sponsored tree planting program in Sacramento, California. Tree and building characteristics and typical weather data are used to model hourly shading and energy used for space conditioning for each building for a period of one year. There were an average of 3.1 program trees per property which reduced annual and peak (8 h average from 1 to 9 p.m. Pacific Daylight Time) cooling energy use 153 kWh (7.1%) and 0.08 kW (2.3%) per tree, respectively. Annual heating load increased 0.85 GJ (0.80 MBtu, 1.9%) per tree. Changes in cooling load were smaller, but percentage changes larger, for newer buildings. Averaged over all homes, annual cooling savings of $15.25 per tree were reduced by a heating penalty of $5.25 per tree, for net savings of $10.00 per tree from shade. We estimate an annual cooling penalty of $2.80 per tree and heating savings of $6.80 per tree from reduced wind speed, for a net savings of $4.00 per tree, and total annual savings of $14.00 per tree ($43.00 per property). Results are found to be consistent with previous simulations and the limited measurements available.
Simpson, J.R. 1998. Urban Forest Impacts on Regional Cooling and Heating Energy Use: Sacramento County Case Study. Journal of Arboriculture, 24(4), 201-214.
Abstract: Urban forests impact energy use for cooling and heating as a result of their moderating influence on climate. To evaluate the regional magnitude of these impacts, a large-scale analysis framework was developed and applied to Sacramento County, California, as a case study. Heating, cooling, and peak electrical energy use changes resulting from modification of solar radiation, air temperature, and wind speed by the existing urban forest were estimated for representative residential and commercial buildings. This is combined with building age and size, canopy and tree cover, and tree density (trees/ha) for 71 county subdivisions. Annual cooling savings are approximately 157 GWh (US$18.5 million) per year—12% of total air conditioning in the county. Net effects on heating are small, with 145 TJ (US$1.3 million) saved annually. Peak energy-use reductions result in avoided costs of US$6 million. The resulting large-scale analysis incorporates a manageable level of detail not previously available. Sensitivity of results to selected input data is demonstrated.
Simpson, J.R. 2002. Improved Estimates of Tree-shade Effects on Residential Energy Use. Energy and Buildings, 34(10), 1067-1076.
Abstract: Tree-shade alters building cooling and heating loads by reducing incident solar radiation. Estimates of the magnitude of this effect, and how it is influenced by urban forest structure (e.g. tree size and location), are difficult due to the complexity inherent in tree–sun–building interactions. The objective of this paper is to present a simplified method for making these estimates appropriate for neighborhood and larger scales. The method uses tabulated energy use changes for a range of tree types (e.g. size, shape) and locations around buildings (lookup tables), combined with frequency of occurrence of trees at those locations. The results are average change in energy use for each tree type that are not explicitly dependent on tree location. The method was tested by comparison to detailed simulations of 178 residences and their associated trees in Sacramento, California. Energy use changes calculated using lookup tables matched those from detailed simulations within ±10%. The method lends itself to practical evaluation of these shading effects at neighborhood or larger scales, which is important for regional assessments of tree effects on energy use, and for development of tree selection and siting recommendations for proposed energy conserving planting programs.
Stone, B., Rodgers, M.O. 2001. Urban Form and Thermal Efficiency: How the Design of Cities Influences the Urban Heat Island Effect. Journal of the American Planning Association, 67(2), 186-198.
Abstract: This article presents findings from a study on residential development patterns and urban heat island formation in the Atlanta, Georgia, metropolitan region. High-resolution thermal imagery collected by the National Aeronautical and Space Administration (NASA) is used in conjunction with parcel-level tax records to examine the interaction between the design of single-family residential parcels and the emission of radiant heat energy. Results from a path analysis illustrate that lower density patterns of residential development contribute more radiant heat energy to surface heat island formation than higher density development patterns within the Atlanta region. Compact moderate-to-high-density new construction and area-based tree ordinances are recommended as policy strategies for mitigating the effects of urban development on regional climate change.
Taha, H. 1997. Urban Climates and Heat Islands: Albedo, Evapotranspiration, and Anthropogenic Heat. Energy and Buildings, 25(2), 99-103.
Abstract: As an introduction to this special issue on urban heat islands and cool communities, this paper reviews some of the characteristics of urban climates and the causes and effects of urban heat islands. In particular, the impacts of surface albedo, evapotranspiration, and anthropogenic heating on the near-surface climate are discussed. Numerical simulations and field measurements indicate that increasing albedo and vegetation cover can be effective in reducing the surface and air temperatures near the ground.
Thayer, R.L. 1981. Designing and Evaluating Energy Efficient Landscape Plantings. Solar Engineering, 6(10), 25-33.
Abstract: Considerations in plant selection and solar access protection are examined. Several shortcuts are provided for assuring that planted landscape will function adequately to conserve energy. The characteristics of the plants that affect energy savings are discussed and include form, ultimate size, growth rate, lead-out period, and branching and leaf density. A California state law protecting solar access (California Solar Shade Control Act of 1978) is examined.
Thayer, R.L., Zanetto, J., Maeda, B.T. 1983. Modeling the Effects of Street Trees on the Performance of Solar and Conventional Houses in Sacramento, California. Landscape Journal, 2(2), 155-164.
Abstract: Street trees have potential for both the beneficial shading of houses during the hot season and the detrimental blocking of incident radiation to solar collectors. Although some states and many local governments have passed regulations to protect solar access from obstruction by vegetation, street tree planners have inadequate data upon which to plan for the necessary trade-offs between providing shade and solar access in much of the temperate United States.
This study describes the computer modeling of the thermal/energy responses of three test houses (solar, conventional, and solar retrofitted) having a continuous row of street trees to the south of the dwelling. Four trees—three deciduous and one evergreen—were tested; each tree was considered at three different setback distances from the south wall of the house. A "no tree" condition was also tested for each house. Predictions were made for annual energy costs for each test house under each tree and setback condition; these results indicated a significant net increase in annual energy costs when street trees were placed in the zone directly south of a solar house.
Thayer, R. L. and B. T. Maeda (1985). "Measuring Street Tree Impact on Solar Performance: A Five-Climate Computer Modeling Study." Journal of Arboriculture 11(1): 1-12.
Abstract: Deciduous trees have been advocated by landscape planners and foresters as ideal "natural" heating and cooling devices for houses and other structures in temperate climates. Conventional wisdom held that deciduous trees blocked unwanted sun from building surfaces in summer, thereby reducing cooling loads, while allowing beneficial sunlight through bare branches to heat building surfaces in winter. This paper attempts to provide empirical information which quantifies the positive and negative effects of deciduous street trees in the solar access zone of conventional (i.e., non-solar) and solar houses. Results of this study underscore a need for concern in placement of street trees and other deciduous or evergreen trees to the immediate south of houses. They are clearly not ideal natural energy conservers when considered in terms of their potential to block solar access and increase winter heating costs. Cost savings between the solar and conventional houses (regardless of tree conditions) are of a greater magnitude than cost savings due to hypothetical removal of street trees. Trees can play secondary and tertiary roles in reducing energy costs. Communities with widespread or increasing use of solar energy should begin re-examining tree planting and management policies with an eye toward reduction of solar access conflicts.
Wagar, J.A. 1984. Using Vegetation to Control Sunlight and Shade on Windows. Landscape Journal, 3(1), 24-35.
Abstract: Precise control of sunlight and shade on windows permits substantial energy savings in the heating and cooling of homes and similar structures. In this investigation, both manual and computerized procedures were developed to guide landscape design to achieve maximum savings. The procedures—which define ideal spatial arrangements of vegetation for windows of various sizes and orientations and for different latitudes and climates—are illustrated for a typical home. Guidelines for choosing suitable species and cultivars are also given.
Wagar, J.A., Heisler, G.M. 1986. Rating Winter Crown Density of Deciduous Trees: A Photographic Procedure. Landscape Journal, 5(1), 9-18.
Abstract: A study was undertaken to develop inexpensive yet accurate procedures for rating trees in terms of winter crown density, which correlates closely with amount of blocked solar radiation. Such procedures provide a basis for identifying better trees for energy-conserving planting. Leafless crowns of 69 trees of three species were photographed. The proportion of each crown image consisting of tree parts was then determined by dot-grid procedures. Crown density was least for the Kentucky coffeetree (Gymnocladus dioica), greatest for Modesto ash trees (Fraxinus velutina 'Modesto'), and intermediate for London plane trees (Platanus x acerifolia). Crown density increased with tree size, and the pattern of this increase differed among species. The azimuth at which trees were photographed did not affect density estimates. The elevation angle at which photos were taken did affect density estimates, but regression procedures permit estimates based on a convenient elevation angle to be adjusted to correspond with estimates based on photos taken at the elevation best expressing the sun's average angle above the horizon during the dates and hours of interest. Photographic and dot-count procedures are rapid, require no specialized equipment, and are well suited to ranking species and cultivars by the density of their winter crowns.
Weidhaas, J. A. 1976. "Goals and Hurdles for Shade Tree Programs." Journal of Arboriculture 2(9): 176-180.
Abstract: A goal suggests a specific result or accomplishment in a designated period of time. It involves action: you have to do something in an orderly manner by a specified deadline. The author lists 10 overall objectives about shade tree programs as related to goals. The goals are grouped into individual and organizational goals and internal and external goals and distinguishes between short-term goals and long term objectives such as the preservation and conservation of trees. Shade tree priorities should no longer be put off by decision-makers in government, in research and educational institutions, in municipalities and counties, or even by us in our own daily activities. Stating that shade trees been considered so essential to environmental quality, challenges, legislation and the need to clarify the roles of the various people and agencies to successful achievements in community shade tree programs.
Westphal, L. M. 2004. Benefits of Trees in an Urban Setting: Selected Bibliography. USDA Forest Service, North Central Res. Stat. Evanston, Illinois: 7pp and CD version.
Abstract: This selected bibliography includes citations for articles under the headings: Social Benefits; Environmental Benefits. The document contains links to several websites with additional information. It also has references to Fact Sheets from the USFA Davis Urban Forestry Lab and Technical Bulletins from the Human Environment Research Lab at the University of Illinois. A CD version is available. There are a number of articles and reports listed in the literature cited.
Wolf, K. 1998. Urban Forest Values: Economic Benefits of Trees in Cities. UW Center for Urban Horticulture, University of Washington. Seattle, WA USA.
Abstract: City-wide, the amount and quality of trees influence both biological and physical urban environments. Plants, if strategically placed and cared for, can become a "living technology," a key part of the urban infrastructure that contributes to more livable urban places.
Wu, C., Xiao, Q., McPherson, E.G. 2008. A Method for Locating Potential Tree-planting Sites in Urban Areas: a Case Study of Los Angeles, USA. Urban Forestry & Urban Greening, 7(2), 65-76.
Abstract: A GIS-based method for locating potential tree-planting sites based on land cover data is introduced. Criteria were developed to identify locations that are spatially available for potential tree planting based on land cover, sufficient distance from impervious surfaces, a minimum amount of pervious surface, and no crown overlap with other trees. In an ArcGIS environment, a computer program was developed to iteratively search, test, and locate potential tree-planting sites by virtually planting large, medium and small trees on plantable areas, with large trees given priority as more benefits are expected to accrue to them. A study in Los Angeles, USA found 2.2 million potential planting sites, approximately 109.3 km2 of potential tree canopy cover.
Youngberg, R. J. (1983). "Shading Effects of Deciduous Trees." Journal of Arboriculture 9(11): 295-297.
Abstract: The shading impact of trees on the energy consumption of buildings, and in particular solar systems is not easy to estimate. With support from the Lincoln Electric system and the U.S. Department of Energy a project was started to monitor deciduous trees, both summer and winter for two years. The project was designed to provide data on widely used tree species in the Midwest. Preliminary analysis of the other monitored trees show a typical 90% blockage during the summer months and a winter blockage ranging from 25 to 60%.