Consumptive Water Use Study

Author : Jesse Ryan Jankowski
Publisher :
ISBN 13 : 9780438930001
Total Pages : pages
Book Rating : 4.9/5 (3 download)

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Download or read book Consumptive Water Use in California’s Sacramento-San Joaquin Delta written by Jesse Ryan Jankowski and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Consumptive water use by crops, often referred to as evapotranspiration (ET), is a substantial element of an agricultural region’s water balance. In the Sacramento-San Joaquin Delta of California, ET data can inform water resource management in a region with coexisting demands for agriculture, cities, the environment, and inter-basin transfers through large-scale water projects. Established methods for the estimation of ET include two-step crop coefficient approaches and computational models which process remotely sensed data from satellites to estimate ET on larger spatial scales based on vegetation characteristics and energy flux data. Though ET estimation methods are well-documented in the literature and have been applied globally, there are few comparisons of estimation methods which discuss the impacts of using different methodologies and input datasets to quantify ET in a region. Furthermore, to date few studies have used multiple methods, field-measured data, and land use surveys to inform water management in a region as complex and important as the Delta. This thesis advances analysis and insights from a comparison of seven established ET estimation models which was previously reported by the Center for Watershed Sciences at the University of California Davis (available at https://watershed.ucdavis.edu/project/delta-et). It covers agricultural and non-agricultural lands in the 679,594-acre Delta Service Area in the 2015 and 2016 water years (October 2014 through September 2016). Land use survey data was used to analyze monthly ET estimates at 30-meter resolutions, and a field meteorological campaign was also done to estimate ET from bare soil, alfalfa, corn, and pasture using surface renewal, eddy covariance, and water vapor flux stations. The total estimated ET from agricultural lands in the Delta was about 1.44 million acre-feet (MAF) in 2015 and 1.38 MAF in 2016, with all seven models within 12% of the ensemble mean and averaging an absolute difference of 6% for both years. While most of this consumptive use originated from the primary crops in the Delta (alfalfa, corn, pasture, and to a lesser degree almonds, tomatoes, and vineyards), increased fallow lands in 2016, open water, and non-agricultural vegetation were also estimated to consume large amounts of water. A detailed comparison between model estimates on satellite overpass days over fourteen two-acre sites revealed that methodological similarities and common input datasets encouraged agreement among models, but the operator judgement and unique assumptions of each model will frequently cause systematic, regional, and temporal differences between estimates. Field-based ET estimates at the same sites were generally lower than model estimates, with a mean bias of -1.2 mm/d and a RMSE of 2.1 mm/d, suggesting that microclimates and other factors unique to the Delta and not factored into models may impact crop ET. Some policy implications arise for enhancing collaborative modeling and measurement of ET in California. These include the potential use of ET data to supplement manual diversion reporting, assist with precision irrigation scheduling, inform water management for ecological restoration, and improve the accuracy of data inputs to models for groundwater management, water quality, environmental protection, and inter-basin transfer operations. A preliminary study comparing ET estimates to reported diversions Delta-wide showed strong agreement in timing and magnitude for several islands and large regions of the Delta. With additional data on local conditions and the places and nature of us of water rights, remote ET estimates may help reduce reporting burdens and streamline water rights administration. Continued and improved land use surveys, field measurement stations, model cooperation and comparison, and a collaborative state consortium to advance ET estimation science and applications in California are recommended and to expand the use of consumptive use data in water resource management.