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October 17, 2017

Future high temperature extremes and soil moisture conditions may cause some regions to become more suitable for rainfed, or non-irrigated, agriculture, while causing other areas to lose suitable farmland, according to a new U.S. Geological Survey study.  

These future conditions will cause an overall increase in the area suitable to support rainfed agriculture within dryland areas. Increases are projected in North America, western Asia, eastern Asia and South America. In contrast, suitable areas are projected to decline in European dryland areas.

This study focused on understanding and projecting suitability for rainfed agriculture in temperate, or non-tropical, dryland regions. Drylands make up at least 40 percent of the earth’s land area and rainfed croplands account for approximately 75 percent of global cropland. Worldwide, temperate regions account for 31 percent of the area used to grow wheat and 17 percent used for corn.

“Understanding the future potential distribution of rainfed agriculture is important for resource managers in meeting economic and food security needs, especially as the earth’s population grows,” said USGS scientist and lead author of the study, John Bradford.

Future climate conditions are expected to increase the frequency of high temperature events and alter the seasonality of soil moisture in dryland systems, which are the factors found to be important in predicting regions suitable for agriculture in these water-limited areas. Findings for the temperate regions examined by this study indicate that many areas currently too cold for agriculture, particularly across Asia and North America, will likely become suitable for growing crops. However, some areas that are currently heavily cultivated, including regions of the United States such as the southern Great Plains, are likely to become less suitable for agriculture in the future.

USGS scientists and an international team of collaborators from Switzerland, Germany, China, Canada and several U.S. universities found that rainfed agriculture is abundant in areas with adequate soil moisture but restricted in areas with regular high temperature extremes. Bradford and collaborators simulated future soil moisture and temperature conditions, and utilized these results to identify where rainfed agriculture may be located in the future. Scientists referenced previously published estimates of rainfed agriculture areas generated using satellite remote sensing. Models were used to determine conditions that support current rainfed agriculture, as well as future suitability under altered climate conditions.

“Our results indicate the interaction of soil moisture and temperature extremes provides a powerful yet simple framework for understanding the conditions that define suitability for rainfed agriculture in drylands,” said Bradford. “Integrating this framework with long-term projections that include rising temperature and changing soil moisture patterns reveals potentially important future shifts in areas that could support agriculture in the absence of irrigation.”  

Within the dryland regions that were the focus of this study, areas suitable for agriculture are those that experience relatively long periods of moist soils and reasonably warm temperatures. In contrast, areas that frequently experience extreme air temperatures above 93 degrees Fahrenheit are less suitable for rainfed agriculture, even if sufficient moisture is available. Even for relatively cool dryland areas, periods of high temperatures during the growing season can negatively affect agriculture suitability. 

Maps illustrate areas that are expected to become more suitable for rainfed agriculture and areas expected to lose farmland.
These maps illustrate areas that are expected to become more suitable for rainfed agriculture (shown in blue), and areas expected to lose suitable farmland (shown in red).  
Dryland agriculture in the Northwestern Great Plains ecoregion.
Dryland agriculture in the Northwestern Great Plains ecoregion. (Credit: Terry Sohl, USGS)

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