Concurrent Irrigation Pauses Can Create Streamflow Pulses for Fish During Critical Low-Flow Periods

Abstract

Streamflow augmentation can support endangered fish during low-flow periods. Irrigated agriculture being the largest out-of-stream consumptive use, there is potential to augment streamflow by temporarily leasing from agriculture. This potential has not been fully realized, perhaps due to a focus on leasing at the extensive margin where land is either irrigated or not. Leasing at the intensive-margin—applying less water on the full land extent—has received limited attention but could be promising, especially related to short-term pulse flows for fish. We address this with two questions: Can a concurrent short-term pause of irrigation withdrawals meaningfully increase streamflow for fish during critical periods? What is the associated foregone crop production and revenue loss? We used the CropSyst model to simulate irrigation demands, yield impacts from a 15-day pause, and resulting revenue reductions for three focal watersheds in eastern Washington State of the United States, and generated water supply curves that provide the marginal cost of augmentation. We evaluated the strategy's ability to bring flows to levels beneficial for fish for at least two consecutive days. Results indicate that a short-term irrigation pause can provide meaningful levels of pulse-flows if conducive conditions related to upstream crop mix, acreage, and augmentation needs are met. The mean cost from lost revenue across years from reduced yields ranged from $1 to $125/acre in scenarios where the targeted streamflow was achieved. This water leasing strategy has potential in some locations to represent a win-win situation for agricultural and environmental stakeholders and warrants further exploration.