Modeling Water Availability for Irrigation in the U.S.
Environmental change is likely to affect global food production, with some regions under heightened risk to droughts, flooding and other disruption. One powerful countermeasure is irrigation: globally, production on a hectare of irrigated land is 2.7 times that on dry land. The future of irrigation, however, depends on the continued availability of significant volumes of fresh water. Food production now accounts for 70% of global freshwater use, and many areas are already water stressed. Environmental change, together with increased demand from other sectors, could exert further pressure on irrigation capabilities by altering the volume and geographical distribution of available water resources. Warmer temperatures could also increase evapotranspiration, and water demands of irrigated crops. Researchers from the Massachusetts Institute of Technology have explored the complex dynamics and interdependencies that define this space, with a particular focus on energy, water, and land systems interactions.
Model simulations under a business-as-usual scenario indicate that environmental change and economic development would increase water shortages and reduce irrigated yields in some regions of the U.S. (particularly the Southwest) where irrigation is not sustainable, and for specific crops including cotton and forage. Yields of other crops (maize, soybean, sorghum, wheat) and regions would increase under this projection. These developments would require adaptive measures that range from growing less irrigation-intensive crops to relocating crop production, with implications for land use elsewhere, indicating the need for comprehensive integrated assessment of these complex economy-earth system interactions.
A critical component of affect the interaction of complex water-energy-land systems is demand for water for irrigation for crop production. A changing environment coupled with increased demand from other sectors, including for energy production, may limit water availability for irrigation, resulting in reduced crop yields. To investigate these complex, multisectoral interactions, researchers at the MIT Joint Program on the Science and Policy of Global Change developed a unique and comprehensive method to quantify the impact of water stress on irrigation while accounting for changes in water resources and competing uses from all U.S. economic sectors. Incorporating a crop-yield reduction module and water-resources model (representing 99 river basins) into the MIT Integrated Global System Modeling (IGSM) framework (an integrated assessment model linking a global economic model to an Earth-system model), they assessed the effects of environmental change and economic development on water availability for irrigation in the U.S. as well as subsequent impacts on crop yields by 2050. The researchers found that under a business-as-usual scenario, water shortages and reduce irrigated yields may occur in some regions (particularly the Southwest) where irrigation is not sustainable, and for specific crops (e.g., cotton and forage). Simulations with less environmental change show reduced effects of water stress on irrigated crop yields. Some level of adaptation would likely be feasible, for example, relocating croplands to regions with sustainable irrigation or switching to less irrigation-intensive crops or more water-efficient irrigation technology.