An online tool is available to help farmers and water managers assess drought and irrigation impacts on water use and crop development. USDA’s Agricultural Research Service has developed an evapotranspiration and drought modeling system at the Hydrology and Remote Sensing Laboratory in Beltsville, Md. It will help forecasters monitor ET and drought conditions across the United States and overseas.

The model, known as ALEXI (Atmosphere-Land Exchange Inverse), uses thermal infrared imagery from satellites and calculates soil and plant temperatures that can be used to create maps of ET rates of plants growing in cultivated areas, forests and natural habitats around the world.

ET consists of the water evaporated from soil and plant surfaces, and the water vapor that escapes, or transpires, through plant leaf pores as the plants absorb carbon dioxide through photosynthesis. Generally, evaporation cools surfaces, so a cooler land surface is an indicator of higher ET rates and wetter soils.

The National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration funded the work. NOAA plans to use the system to generate ET estimates over the continental United States.

ALEXI has been estimating ET rates since 2000, but the researchers continue to refine the system and plan to make the maps available online on the U.S. Drought Portal at