Connections between Cropping Trends, Water Availability, and Groundwater Regulations in Arizona

Abstract

Arizona is a highly productive region for agriculture due to its long growing season, high crop yields, and historically reliable water supplies. However, the arid climate means that agriculture relies almost exclusively on irrigation via surface water deliveries and groundwater pumping. Surface water deliveries are limited to areas near the Colorado River, Central Arizona Project (CAP), and the few perennially flowing river systems in the state. Groundwater is more widely accessible and is used in other areas of the state which don’t have access to surface water, and to supplement surface water supplies. Groundwater is regulated within some designated areas but remains unregulated across the majority of the state. Our goal is to explore whether the type of water source (groundwater, local surface water or imported surface water), or groundwater regulations have influenced historical cropping patterns across Arizona. We present a retrospective analysis of cropping patterns across the state of Arizona using satellite data from the United States Department of Agriculture National Agricultural Statistics Service (USDA NASS). We divide our analysis into geo-regions that are defined based on water supply types and regulation. Results show that irrigated acres statewide have remained consistent from 2008-2020. However, the Central and Southeastern geo-regions are experiencing acreage increases in high water use and hard to fallow crops, such as alfalfa and trees. The Lower Colorado River geo-region, despite high water security based on senior water rights, has the largest increase in low water use crops. Comparing unregulated and regulated groundwater areas we find that irrigated acres are increasing in unregulated regions while decreasing in regulated regions. Results indicate that regions of the state which are groundwater dominated are experiencing increases in acreage of high water use crops, in contrast to surface water dominated regions which have growing acres of low water use crops. With surface water cutbacks imminent, the risk of unsustainable pumping or increased fallowing could have profound impacts on the state’s economy and groundwater levels.