ADO Factsheet: Standardized Precipitation Index (SPI)

The Standardised Precipitation Index (SPI) is the most commonly used index worldwide for detecting and characterising meteorological droughts. A meteorological drought is defined as a period with abnormal precipitation deficit, in relation to normal conditions for a region, represented as a long-term average. The SPI shows the normalisedanomalies (deviations from the long-term average) of the observed total precipitation for any given location and accumulation period of interest. The name of the index is usually modified to include the accumulation period. SPI-3, for example, refers to accumulation period of three months (JRC EDO, 2020).