Composite Drought Indices

 To capture the extent and severity of current drought conditions, various indicator data sets on weather, soil moisture, evapotranspiration, and crop conditions are combined. Drought conditions can then be defined using a composite drought index (CDI) which captures the nature and characteristics of current drought conditions at the regional and country levels.

The definition of a CDI in an area as naturally arid as the MENA region will be different to those used in wetter areas. The MENA CDI incorporates:

  • Vegetation health anomalies from the Normalized Difference Vegetation Index (NDVI) anomaly from MODIS which captures the state of stress within crops relative to average conditions for the month
  • Surface temperature anomaly from MODIS highlighting whether conditions are warmer/cooler than usual for that month
  • Precipitation anomalies captured through the Standardized Precipitation Index (SPI)using CHIRPSdata highlighting whether it is wetter/drier than usual for that month
  • Soil moisture anomaly generated through the LISmodel capturing whether the rooting zone soil moisture is drier/wetter than usual for the month
  • Actual evapotranspiration anomaly from ALEXI

The CDI definitions are developed for each country and for the region and tested against observations and from evidence of drought occurrence and impacts. Following testing and from discussions in-country using local knowledge,the CDIswere refined through so that they better represent drought conditions and impacts. The CDIs used in the MAWRED knowledge hub are a product of extensive collaboration with partners in the region as well as international experts from the US National Drought Mitigation Center at the University of Nebraska-Lincoln.