Estimating Crop Consumption of Irrigation Water for the Conterminous U.S.

Abstract

Abstract. Water consumption for crop irrigation is the largest single use of water in the U.S. but is poorly quantified because of limitations in data and the inherent challenges in measuring water consumption. In this study, water consumption for irrigated agriculture was estimated across the U.S. to improve understanding of water budgets in different regions. Published data on cropping patterns and water application were used in conjunction with a national-scale analysis to estimate water application and crop water consumption using the SWAT (Soil and Water Assessment Tool) watershed model. Crop water consumption estimates were based on evapotranspiration, with supporting information on the diversity of crops, irrigated area, water quantity and source, and local weather conditions. Quantification of water consumption supports broader analyses of the food-energy-water nexus and allows evaluation of the efficiency of irrigation water use at different spatial scales. Focusing on 2005 data, it is estimated that 60% of water reported as withdrawn from various sources is applied to fields, indicating a potentially large and poorly understood conveyance loss that occurs in a small number of states. Of the field-applied irrigation water, roughly 65% is directly used by crops or is lost in the field, with large regional variations. This may be compared to consumption estimates in prior studies that ranged from 16% to 90%. Areas that dominate the national aggregate estimate of crop water consumption include California’s Central and Imperial Valleys, areas overlying the Ogallala Aquifer in the central U.S., the Lower Colorado Basin, and the eastern part of the Pacific Northwest Basin. Keywords: Crop water use, Irrigated agriculture, SWAT, Watershed model, Water withdrawal.