Drought monitoring is based on various indices: the standardized precipitation index (SPI), which shows the deviation from average precipitation and is therefore directly related to drought hazard, while additional indices monitor the status of soil moisture, vegetation, groundwater levels, etc. to assess the potential impacts of droughts.
A method that combines different drought indices (SPI, soil moisture anomalies
and fAPAR anomalies) is proposed in order to identify areas affected by agricultural
drought and also areas with the potential to be affected. The method outcome is the Combined Drought Indicator (CDI) consisting in a classification scheme based in three drought impact levels ("Watch", "Warning" and "Alert"), corresponding to the different stages of the idealized agricultural drought cause-effect relationship. Two additional levels, "Partial recovery" and "Recovery", identify the stages of the vegetation recovery process.