A Comparative Study of Evapotranspiration Estimates for the California's Sacramento-San Joaquin Delta

An improved overall understanding of consumptive water use in the California's Sacramento-San Joaquin Delta is critical not only for water rights administration but also for agricultural irrigation management, regional water planning, and environmental and water quality protection. The purpose of this project is to develop a better understanding of consumptive water use in the Delta by coordinating modeling, measurement and other information derived from independent research efforts. Participating organizations include the University of California, Davis (UC Davis), the California Department of Water Resources (DWR), the Office of the Delta Watermaster, the California Polytechnic State University, San Luis Obispo, NASA-Ames Laboratory Monterey, and the USDA-ARS. The project will consolidate information about methods for measuring and estimating consumptive water use within the Delta. The Center for Watershed Sciences of UC Davis oversees the study and will analyze and disseminate modeled and measured evapotranspiration for crops and other land use classes in the Delta. Field measurements are made using eddy covariance, surface renewal and eddy-covariance energy budget residual evapotranspiration (ET) stations over three dominant crop types. A selection of ET methods are implemented to estimate field-scale ET across the Delta area, involving remotely sensed data, and ground level meteorological stations. Methods include Cal-SIMETAW and DETAW modeling (DWR), and remote sensing based approaches: 1) METRIC (UC Davis, Cal Poly San Luis Obispo, NASA-Ames), 2) Priestley-Taylor (UC Davis), 3) DisAlexi (USDA-ARS) and 4)WRF-ACASA (UC Davis). This paper provides preliminary results’ insights from comparing evapotransporation estimates for the 2015 irrigationn season in the Sacramento-San Joaquin Delta from modeling using the aforementioned methods and bare soil ET measurements. Challenges, limitations and work ahead under this collaborative research are discussed.