Drought Early Warning And Decision Support
Use Case Description
“Drought” is a composite term that refers to a range of meteorological, agricultural, and hydrological deficits. Each type of drought therefore requires different indicators. Consequently, drought early warning systems can range from single index monitoring to true systems integration covering multiple indices.
Traditional EO-assisted early warning often relies on individual drought indicators, each capturing a specific dimension of drought. Rainfall-based indices like the Standardized Precipitation Index (SPI) or GRACE Groundwater Drought Index (based on GRACE data) provide information about the possible causes of drought. Soil moisture indices derived, for instance, from microwave sensors (SMOS, SMAP) measure root-zone water availability, bridging the gap between meteorological drivers and vegetation response. Finally, vegetation indices such as NDVI, VCI, TCI, and VHI (relying, for instance, on Landsat, AVHRR, MODIS) monitor actual impacts on plant health, often in combination with phenological models to define the start and end of the growing season. In addition, proxy indicators like land surface temperature and evapotranspiration are widely used in drought monitoring.
The Combined Drought Indicator (CDI) developed for the European Drought Observatory (EDO) is an example of a multi-index drought early warning system covering precipitation shortage (the cause), soil moisture deficit (the intermediate state) and vegetation productivity reduction (the effect). Each stage corresponds to distinct warning levels—”Watch,” “Warning,” and “Alert”—enabling authorities to anticipate agricultural impacts before they fully materialize. Another example is FAO’s Agricultural Stress Index System (ASIS) which, after calibration with in-country data, provides 10-day updates on the severity of drought stress of agricultural areas. An easy-to-understand classification into areas under slight, moderate, severe and extreme drought stress helps decision-makers take appropriate action.
By providing early warnings of drought, these systems enable communities to prepare ahead of time, for example, by adjusting agricultural practices, managing surface and groundwater resources, or providing financial assistance to farmers if needed.
