Drought forecasting is based on forecasted gridded time series of storage in the upper groundwater zone (EFAS driven by IFS-SEAS) for the whole of Europe and at regional scale. Two approaches are used, that is the Standardized Precipitation Index (SGI) and the threshold level method (TLM).
The SGI provides the severity of the drought in groundwater storage as the number of standard deviations from the median (e.g. SGI=-2 says that the precipitation is 2 standard deviation from the median).
The TLM forecasts the onset, duration, and severity (deficit volume) of the drought in groundwater storage in probabilistic terms. The drought occurs when the groundwater storage is below the threshold.
The SGI also provides the total drought affected area. The probabilistic forecasts are presented as 25th percentile, median, and 75th percentile of the 51 ensemble members.