Combined Drought Indicator (CDI)
Index name: Combined Drought Indicator (CDI).
Ease of use: Green.
Origins: Developed by Sepulcre-Canto et al. at the European Drought Observatory as a drought index for Europe in which SPI, SMA and fraction of Absorbed Photosynthetically Active Radiation (fAPAR) are combined as an indicator for droughts affecting agriculture.
Characteristics: Composed of three warning levels (watch, warning and alert) by integrating three drought indicators: SPI, soil moisture and remotely sensed vegetation data. A watch is indicated when there is a precipitation shortage, a warning level is reached when the precipitation shortage translates into a soil moisture shortage, and a warning occurs when the precipitation and soil moisture deficits translate into an impact to the vegetation.
Input parameters: SPI computed from station-based precipitation data throughout Europe; in this case, the three-month SPI is used. Soil moisture data are obtained using the LISFLOOD model, and fAPAR comes from the European Space Agency.
Applications: Used as an indicator of droughts with agricultural impacts.
Strengths: The spatial coverage is good and at a high resolution using a combination of remotely sensed and surface data.
Weaknesses: Using a single SPI value may not be the best option in all situations and does not represent conditions that may carry over from season to season. Hard to replicate and currently not available for areas outside Europe.
Resources: Housed and maintained at the European Drought Observatory within the European Commission’s Joint Research Centre, http://edo.jrc.ec.europa.eu/edov2/php/index.php?id=1000.
Reference: Sepulcre-Canto, G., S. Horion, A. Singleton, H. Carrao and J. Vogt, 2012: Development of a Combined Drought Indicator to detect agricultural drought in Europe. Natural Hazards and Earth Systems Sciences, 12:3519–3531.