Evaluating the hydrologic impact of an irrigation curtailment program using Landsat satellite data in the Upper Klamath Basin

Meeting demand for agricultural water use and environmental water requirement has become a challenge for the Upper Klamath Basin that stretches across southern Oregon and northern California. This basin is home to several threatened and endangered species and to more than 200,000 ac of irrigation land on the U.S. Bureau of Reclamation's (USBR) Klamath Project. Since the 2013 adjudication of water right claims in the basin, curtailment of irrigation diversions have occurred in the tributaries to Upper Klamath Lake. We combined Landsat-based evapotranspiration (ET) data obtained from the Operational Simplified Surface Energy Balance (SSEBop) model with gridded precipitation and streamflow data and station discharge data to quantify water savings from the curtailment program. Analyses were performed for two baseline years (2004 and 2006) and four target years (2013-2016). First, Landsat scale ET maps were derived and anomalies in consumptive water use for baseline and target years were estimated. This information was then combined with gridded rainfall, gridded runoff and stream gauge data to generate volumetric savings (extra water available) from the irrigation curtailment program. The ET analysis also quantified the source of the extra water available from surface water, groundwater, and conjunctive water use irrigation types. With respect to the baseline years, our results indicated the potential increase to stream flow (extra water available) because of savings from irrigation over June to September were the highest in 2013 and gradually declined thereafter. For example, for the Sprague River at Chiloquin station, irrigation water savings for 2013, 2014, 2015, and 2016 were 16,300, 6,000, 800, and 0 ac-ft, respectively. Our estimates of extra water available from irrigation curtailment were found to agree well with other independent assessments. This study demonstrates, for the first time, the use of remote sensing-derived information (Landsat-based ET and other remote sensing datasets) for quantifying the extra water available from the irrigated curtailment program.