Rangeland Climate and Drought

Written by Rachel Frost, Montana State University

Drought is once again threatening rangelands across the Western United States. The Rangelands CoP has gathered a list of resources for rangeland and grazing management before, during, and after droughts. Visit Rangeland Drought Resources for more information.

Climate and Drought

Perhaps no single factor influences the amount and kind of vegetation growing on rangelands more than the climate, particularly precipitation.  The lack of sufficient precipitation at the appropriate time of year is drought.  Understanding how changes in climate patterns, both regionally and globally, cause and drive episodes of drought is an important consideration on rangelands. Drought can be devastating to rangelands and agricultural production. Our ability to respond to or recover from the effects of drought requires strategic planning and mitigation strategies.

What constitutes a drought?

Drought is defined in several ways: 

• Meteorological drought
  Defined as lower than "normal' precipitation, generally 3/4 or less of average annual precipitation is considered a drought.
• Agricultural drought
  When water deficits limit vegetation production
• Hydrologic drought
  Period when surface and groundwater levels availability is inadequate to supply esablished uses
• Socio-economic drought
  Period of water shortage that directly affects people's lives through lost choices and changes in behavior (i.e. water rationing)
             See more information on the economic impact of droughts

From: Thurow and Taylor, 1999. Viewpoint, the role of drought in range management. Journal of Range Management. 52: 413-419.

Effects of drought on rangeland vegetation.

The biggest effect on rangeland vegetation  is that there is less of it.  Total production can be dramatically reduced on rangeland receiving sub-normal precipitation especially during the growing season. However, reductions are generally less on ranges in good ecological condition. The ability of plants to recover following drought is dependant on their vigor before and during the drought.  The extent to which plants are grazed also affects their ability to recover from drought.  Excessive grazing (more than 60% of current season's growth) reduces vigor, while moderate use (25 to 55%) does not impair vigor or recovery rate.

Weeds and poisonous plants may increase during drought because they are seldom grazed by livestock and therefore are better able to regrow once precipitation returns. Even if densities of poisonous plants do not increase toxicity problems may occur more often because there is a shortage of residual forage from the year before to help buffer the toxins.  Many poisonous plants initiate growth early in the spring when livestock are seeking green forage and before grasses have begun to grow. 

For more information about the effects of drought on rangeland vegetation visit: 

Effects of climate change on sagebrush regeneration at the leading and trailing edge of its distribution
Response of common plants to annual climate variation in sagebrush communities
Carbon cycling in sagebrush steppe under climate change
Paleorecords of Sage Steppe Communities

Grazing management during drought.

There are several ways that managers can alter their grazing to prevent damage to the range resources during drought. 

• Reduce livestock numbers
  this will reduce the overall forage demand of the herd and balance forage supply with forage demand.
• Wean calves early 
  Dry cows consume about 35% less forage than lactating cows and it eliminates the forage consumed by the calves.
• Lease additional pasture
  Lease additional pasture or graze tame pastures as they can handle excessive use more than native forages.
• Delay turnout in spring
  Delay turnout in spring as much as possible to allow plants an opportunity to recover vigor.  This will also lessen potential problems from grass tetany and poisonous plants.
• Rotate pastures
  Rotate pastures more frequently in rotational grazing systems.
• Alter season of use for pastures whenever possible
  If areas were grazed early the previous year, then try and delay grazing until plant maturity this year.

How to plan and prepare for drought.

Taylor and Thurow contend that "Drought is an inevitable part of normal climatic fluctuation and should be considered as part of a recurring, albeit unpredictable environmental feature which must be included in planning." 

The first step to developing a drought-survival plan is to determine how much forage you have and how long it will last. You must be able to balance forage demand by livestock with forage availability. Ideally, managers should develop a culling strategy prior to drought. Using stocker animals as a percentage of the ranch's normal carrying capacity allows for more flexibility in stocking rate. Develop a supplementation strategy to direct feed to where it will be most effective for production status of the herd. Having a controlled calving season will reduce the age variability in cows and calves and allow for more efficient supplementation. . ..

More information on the Economics of Drought Management

For more information see Drought Strategies Publications website produced by Texas AgriLife Extension.