Calculator for Evaluation of Crop Water Use Fractions in California

Thursday, 18 December 2014
Lee Johnson1, Florence Cassel-Sharma2, Dave Goorahoo2 and Forrest S Melton1, (1)Univ. Corp. Monterey Bay, Moffett Field, CA, United States, (2)CSU Fresno, Fresno, CA, United States
The California Water Conservation Act of 2009 includes a call for improved quantification of agricultural water use efficiency. Metrics for quantifying irrigated agricultural water use can help evaluate irrigation system performance and assess strategies for improved water management. In support of this legislation, the California Department of Water Resources (CDWR) recommends various metrics to help identify opportunities for improving agricultural water use efficiency. Included among these are the Crop Consumptive Use Fraction (CCUF), which evaluates crop consumptive use relative to total applied water, and the Agronomic Water Use Fraction (AWUF), which considers additional beneficial uses of water including soil salinity management, land preparation, and frost protection. A prototype calculator has been built to provide users with a consistent and practical means to derive these metrics over seasonal to annual timeframes. The tool combines Landsat optical data from NASA's Satellite Irrigation Management Support System with reference evapotranspiration from CDWR's California Irrigation Management Information System to estimate crop consumptive water use and evaluate CCUF for non-stressed crops on drip or micro-sprinkler delivery systems. A soil water balance model can then be applied to refine the estimate for crops under deficit irrigation or serviced by sprinkler, flood or furrow water delivery systems during all or part of the season. For AWUF derivation, the user specifies additional values related to agronomic water use, if known, or may use available on-board tools to estimate these values under best professional practices. The calculator operates on several major annual/perennial crop types. Additional input parameters include growing region, season, soil texture, precipitation, and irrigation amount/method.