Magnitude of meteorological droughts

The index magnitude of meteorological droughts combines information about the duration and severity of droughts. It is defined as the positive sum of the SPI for all the months within drought events in a given year, thereby giving more weight to months with severe droughts than those with less severe droughts (see the ETC-CCA Technical Paper for details). For consistency with ‘Duration of meteorological droughts’ above, this index is also based on SPI-3 and a threshold of -1 is used to identify drought occurrences. Alternative aggregation periods for SPI can be used depending on the type of drought considered and the specific applications.