Over half of the United States is experiencing some level of drought, with about 10% seeing “extreme drought”. Rainfall totals and soil moisture content are the typical ways to measure drought but the ESI may provide more information.
“The Evaporative Stress Index (ESI) describes temporal anomalies in evapotranspiration, highlighting areas with anomalously high or low rates of water use across the land surface.” Evapotranspiration is the sum of evaporation and plant transpiration from the Earth’s land surface to the atmosphere.
ESI values quantify standardized anomalies in the ratio of actual to potential evapotranspiration. The data is derived using thermal infrared satellite imagery.
Translation: The areas in red have less water movement from land/plants to atmosphere than “normal”. The ares in green have more water movement than “normal”.
Credit: USDA, ARS-HRSL