Understanding the Impact of Sustainable Water Use on US Irrigated Agriculture.

Water demand is increasing due to population growth and increases in power generation. In areas where water is scarce, farmers face water shortages and have to reduce irrigation applications or cultivated area. To prevent aquifer depletion, groundwater usage should not exceed aquifer recharge rate. In this work, we calculated the impact on yield of sustainable water use for maize, soybean, and cotton across the United states using a parallel version of the Decision Support System for Agrotechnology Transfer (DSSAT). Model uncertainty in water usage was estimated by comparing evapotranspiration and water use with remotely sensed and survey data.

We estimated sustainable irrigation levels using data from the United States Geological Survey (USGS) on aquifer recharge rates and irrigation water use per county. In regions where groundwater use surpasses recharge, sustainable water use was calculated by reducing the groundwater portion of irrigation water use. We evaluated crop seasonal evapotranspiration over 5 arc-minute grids, and irrigation water use at the county level. DSSAT evapotranspiration was assessed only for rainfed agriculture to test model evapotranspiration equations separate from the irrigation algorithm. DSSAT evapotranspiration was evaluated against the Atmospheric Land Exchange Inverse (ALEXI) modeling product. Irrigation water use was compared against the USGS county level irrigated agriculture water use survey data.

The results of this work highlight the counties that will face the greatest yield reductions if groundwater pumping rules were to be implemented. Most of the affected counties are located in the Great Plains and western US.