WaterSMART - Evapotranspiration (ET)

The WaterSMART (Water for Sustaining and Managing America's Resources for Tomorrow) initiative of the U.S. Department of the Interior (DOI) is implemented through the U.S. Geological Survey (USGS) Water Census program to meet the objectives of the Water Use and Availability activity. The USGS Water Census aims to quantify the year-to-year variability of vegetation water use (consumptive use), with a focus on irrigated lands, in a cost-effective and timely manner, i.e., previous year consumptive use estimates to be available before the next irrigation season starts. We improve upon existing hydrologic models to estimate and validate evapotranspiration (ET) from irrigated lands and the general landscape using a combination of satellite data and weather datasets.

The USGS EROS approach to ET estimation allows the quantification of ET at two important scales: (1) field and (2) hydrologic basin. Field-scale ET is used for water use estimation to understand and quantify where, by whom, and how much water is being used in the landscape. On the other hand, basin-scale ET assists in understanding basin water balance and water availability. Quantifying water use and water availability is a critical component of the Water Census objectives. Irrigation water use information is used for the planning and implementation of water resources allocation and curtailment guidelines. Similarly, ET information is critical in understanding groundwater withdrawal and recharge rates, as well as for drought monitoring. The primary users of this product are State water engineers and hydrologists, Bureau of Reclamation, and USGS water scientists.