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Agricultural irrigation is the largest consumer of water in the United States. Many changes have occurred over the years, but we question the recent attention on efficiency. Comparing 2015 and 1985, we find that more land is being irrigated with less water: irrigation withdrawals fell by 14%, irrigated area expanded by 11%, and flood irrigation was substantially displaced by sprinkler and microirrigation systems. However, consumptive water use fell by only 1%, and return flows-an important part of the water balance that supports many downstream needsdeclined by 39%. This gain in efficiency and loss in return flow, without any apparent saving of water, is the conflicting legacy of U.S. irrigation. We propose the links among irrigation efficiency, return flows, and consumptive water use as a central theme around which to organize future irrigation research, policy, and management. We call on state and federal agencies that fund research and adoption of improved irrigation practices to require accounting of all aspects of the water balance-including return flow-and promote sustainable, basin-scale water conservation.
Sowby et al. (Thu,) studied this question.