Estimating irrigation use and improving water resources management using energy balance (METRIC) estimates of evapotranspiration

Water managers require information and analytical tools to estimate crop evapotranspiration (ET) and irrigation water requirements in large irrigated areas. Conventional ET computations use spatial information on crop types and ground-based meteorological data to estimate ET over an irrigation season. The satellite-based surface energy balance method METRIC generates instantaneous ET estimates from satellite imagery and conventional weather data for multiple dates over the course of a growing season and are used to compute monthly and seasonal ET over large irrigated areas. Three water management applications of the METRIC method for ET estimation are presented: 1) ET estimates in the South Platte River basin for 200 irrigation ditches, and nearly 500,000 acres, are compared with ET derived from traditional methods for the Colorado Decision Support System, a State of Colorado program for improving water management; 2) estimates of ET in the upper North Platte River basin for monitoring an interstate water compact; 3) water balance analyses estimating irrigated crop ET from both surface and groundwater in representative study areas of the Oum Er Rbia basin in Morocco as part of a World-Bank funded initiative to improve the efficiency of irrigation projects. The METRIC method offers particular advantages in areas where water delivery records are sparse or unreliable, and in regions with highly variable irrigation consumptive use due to variable cropping patterns, agronomic practices and physical conditions.