The global Historical Drought Risk products capture historical risk of drought across the
globe using well-established drought monitoring metrics such as Standardized Precipitation
and Evaporation Index (SPEI). This risk indicator was computed using the monthly time series of
SPEI at six time scale (6-month, 12-month, 18-month, 24-month, 30-month, and 32-month) and applying
the relative frequency approach – the ratio of the number of months when the index is below or
equal to a threshold indicating drought of moderate magnitude (SPEI < -1) to the total number
of possible outcomes, considering the last 11 years (January 2011 – December 2022) as a reference period.
These products are categorised into short-term and long-term drought blends for different applications.
Short-term products are more suited towards vegetative and agricultural drought monitoring, while the long-term products are more suited towards hydrological drought monitoring.