Evaporative Stress Index (ESI)

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. ESI values quantify standardized anomalies (σ values) in the ratio of clear-sky actual-to-potential ET (fPET), derived using thermal infrared (TIR) satellite imagery from MODIS. To capture a range in timescales, fPET composites are developed for 4-week and 12-week moving windows, advancing at 7-day intervals. Standardized anomalies are then computed with respect to normal conditions (mean and standard deviation) for each compositing interval assessed over a period of record from 2000-2017.

These 4 week and 12 week datasets are exposed via temporal WMS services, TIF file download, and also via the SERVIR ClimateSERV application. Through ClimateSERV, the SERVIR Program provides the ability to extract zonal statistics (average, min, max) over a user-specified area of interest (AOI) for a specific time period. Data is downloadable as charts and underlying tabular data (in comma separated values - .csv files). Subsets of the data in raster format (.tif files) for an AOI can also be extracted. ClimateSERV also exposes an API to allow data retrieval requests into third party applications. Please see respective Online Resource links below.