GDO Standardized Precipitation Index ERA5, 1-month accumulation period (SPI-1) (version 1.0.0)

Collection: DROUGHT : Drought Observatories datasets 


The 1-month Standardized Precipitation Index (SPI-1) is an indicator used to monitor meteorological drought based on precipitation anomalies over 1-month accumulation periods. SPI-1 serves as a proxy indicator for immediate impacts of droughts such as reduced soil moisture, snowpack, and flow in smaller creeks. This indicator is calculated with one month total precipitation accumulation period (SPI-1), derived from the fifth generation ECMWF reanalysis for the global climate and weather ERA5 ( hourly precipitation data; using a reference period between the year 1991 and 2020. Data at the moment have a monthly computation but in the future version 2.0.0 they will be actualized every 10 days, thus giving a more actual overview of the indicator than the classical end-of-month computation. The accumulation periods will remain however monthly, with monthly windows (28-, 29-, 30-, or 31-day periods) starting on the 1st, 11th and 21st day of the month. The SPI represents precipitation anomalies at a given location and time, as the deviation from the long-term mean in a standard-normal distribution, with more negative values representing a more severe drought. SPI is calculated by comparing the observed total precipitation amounts for an accumulation period of a number of months, indicated by a number following SPI-, with the long-term “climatological” rainfall distribution for that same period of the year, derived from historical rainfall records in a specific reference period. A given accumulation period corresponds to different potential impacts of a drought, with shorter accumulation periods generally representing fast-changing aspects of the water system such as surface soil moisture and flow in small rivers, and longer accumulation periods representing slower changing aspects of the water system such as groundwater and baseflow in larger rivers. However, the exact relationship between accumulation period and impacts depends on the natural environment (e.g. geology, soils) and human interference (e.g. irrigation). Details on the calculation of the SPI are given in the indicator factsheet.


Alfred.DE-JAGER (at)


  • European and Global Drought Observatories, EDO

How to cite

European Commission, Joint Research Centre (JRC) (2024): GDO Standardized Precipitation Index ERA5, 1-month accumulation period (SPI-1) (version 1.0.0). European Commission, Joint Research Centre (JRC) [Dataset] PID:


CEMS Copernicus Drought ECMWF ERA5 European Drought Observatory (EDO) Global Drought Observatory (GDO) Precipitation Precipitation Anomaly SPI

Data access

Data Download Service URL


The relationship of drought frequency and duration to time scale.
McKee, T.B., N.J. Doesken and J. Kleist. 1993. The relationship of drought frequency and duration to time scale. In: Proceedingsof the Eighth Conference on Applied Climatology, Anaheim, California, 17–22 January 1993. Boston, American Meteorological Society, 179–184

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Spatial coverage

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Temporal coverage

From date To date
1982-01-01 N/A

Additional information

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European Commission, Joint Research Centre
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