The Evaporative Stress Index (ESI) describes temporal anomalies in evapotranspiration (ET), highlighting areas with anomalously high or low rates of water use across the land surface. Here, ET is retrieved via energy balance using remotely sensed land-surface temperature (LST) time-change signals. LST is a fast-response variable, providing proxy information regarding rapidly evolving surface soil moisture and crop stress conditions at relatively high spatial resolution. The ESI also demonstrates capability for capturing early signals of “flash drought," brought on by extended periods of hot, dry, and windy conditions leading to rapid soil moisture depletion.
(from https://www.drought.gov/data-maps-tools/evaporative-stress-index-esi)
www.nws.noaa.gov
