Alleviating Water Scarcity by Optimizing Crop Mixtures

Abstract Irrigated agriculture dominates freshwater consumption globally and has led to widespread drying of rivers and depletion of aquifers in regions where water demand exceeds naturally replenishment. In the US, this mismatch between irrigation demand and freshwater availability – combined with recurrent droughts and ongoing climate change – has meant that many farmers are experiencing water shortages. Yet there has been no spatially detailed assessment of where and to what extent the irrigation demands of specific crops contribute to water source depletion across the country. Here we combine modelled crop water requirements and detailed agricultural statistics within a national hydrological model to quantify sub-basin-level depletion, revealing high to severe levels of irrigation scarcity in 30% of sub-basins in the western US, with cattle-feed crops – alfalfa and other hay – being the largest water consumers in 57% of the region’s sub-basins. We also assessed recent trends in irrigation water consumption, crop production, and revenue generation in six high-profile farming areas and find that in recent decades, water consumption has decreased in four of our study areas – in large part due to due to shifts in the production of the most water-consumptive crops – even while farm revenues increased, suggesting the opportunity to decouple irrigation consumption from revenue generation. To examine opportunities for crop shifting to realize further reductions in water consumption, we then performed optimizations on feasible crop mixtures while holding farm revenues constant, finding that additional water savings of 21–59% are possible. These findings demonstrate strong opportunities for economic and environmental co-benefits in irrigated agriculture and provide both hope and direction to regions struggling with water scarcity around the world.