Water Use by Agricultural Crops and Riparian Vegetation: An Application of Remote Sensing Technology

Abstract

New Mexico is experiencing great changes in land use, population growth and cropping patterns. These changes, combined with extended drought, provide challenges to the management and appropriation of the state’s limited water supplies. Currently, more than 75 percent of New Mexico’s water is used in agriculture. Furthermore, exotic riparian vegetation such as saltcedar results in signifi cant water consumption throughout the state. Evapotranspiration (ET), or water use by crops and riparian vegetation, is a true depletion or loss from a hydrologic system. Estimates of ET values are used in irrigation water management, water rights allocation, hydrologic modeling, as well as overall water resource planning and management. Traditionally, crop ET is estimated by multiplying aggregate crop coeffi cients (Kc) by a standardized reference evapotranspiration (ETsz) (Allen et al. 2005). The Kc represents plants and the soil environment while ETsz represents climatological factors that provide the energy that drives ET. However, this methodology is limited to localized estimation of ET and is not practical or economical for large scale use due to spatial and temporal variability of vegetation, soils, and management techniques. Recently developed technologies use sensors that can directly measure ET over the vegetation canopy. However, these technologies are costly and are limited to small areas. While direct measurement provides localized values of ET, these measurements are limited and do not account for the diversity of ET across the watershed. Remote sensing technology combines ground measurement of ET with large scale remotely sensed vegetation canopy data and ground level climatological data to calculate regional values of ET. This combination of groundlevel and remotely sensed data provides the most advanced and economical approach for estimating ET over a large area.