Pairing OpenET remotely sensed evapotranspiration with streamflow data to assess the effectiveness of irrigation curtailment for aquatic conservation Journal of Hydrology

As droughts worsen in water-scarce regions, tools to more precisely manage water use will become increasingly important. In particular, managing water supply at the basin scale requires tracking and managing consumptive water use. Remote sensing can quantify changes in evapotranspiration (ET), the primary component of agricultural consumptive water use. Our unique contribution here is to illustrate how to pair remotely sensed agricultural ET with streamflow gage data to assess the hydrologic effects of irrigation curtailment regulations. We employed the satellite-based OpenET to measure ET in two neighboring valleys in California, USA, comparing a baseline year (2020) with a curtailment year (2022) when water extraction was restricted to protect salmon. We used statistical models to account for climate-driven variation in streamflow, isolating the effects of curtailment. We detected substantial ET reductions following irrigation curtailment in Shasta Valley, where streamflow also increased following the curtailment policy. In Scott Valley, ET and streamflow were not affected by curtailment. Differences between the two valleys that could result in the observed patterns include crop type, surface vs. groundwater dependence, and regulatory context. Our findings highlight the need for clear baseline data on irrigation practices to support curtailment design and direct monitoring of applied water use. We found that OpenET is an effective tool for quantifying changes in consumptive water use and assessing the effectiveness of water management actions in places with limited data. This novel methodology may be applied in the future to pair field-scale changes in consumptive use to regional water resources management outcomes.