Presentation of Four Centennial-long Global Gridded Datasets of the Standardized Precipitation Index

Abstract In this article four global gridded datasets of the Standardized Precipitation Index (SPI) are presented. They are computed from four different data sources: UDEL/GEOG/CCR v3.02, GPCC/ v7.0, NOAA-CIRES 20CR v2c and ECMWF ERA-20C each covering more than a century-long period. The SPI is calculated for the most frequently used time windows of 1, 3, 6, and 12 months. UDEL/GEOG/CCR v3.02 and GPCC/ v7.0 are used in the highest native resolution of 0.5×0.5° whilst NOAA-CIRES 20CR v2c and ECMWF ERA-20C are interpolated at 1.5×1.5° and 0.5×0.5° correspondingly. In contrast to some other indices, for example the popular Palmer Drought Severity Index (PDSI), SPI has significant advantages such as simplicity, suitability on variable time scales and robustness rooted in a solid theoretical development. SPI has been selected by the World Meteorological Organization (WMO) as a key indicator for monitoring drought (‘Lincoln declaration’). As a result, drought monitoring centres worldwide are effectively exploiting this index and the National Meteorological and Hydrological Services (NMHSs) are encouraged to use it for monitoring meteorological droughts. These facts and the strong conviction of the authors that the free exchange of data and software services are а basis of effective scientific collaboration, are the main motivators to provide these datasets free of charge at The paper briefly presents some possible applications of the SPI data, revealing its suitability for various objective long-term drought studies at any geographical location.

Keywords Global Gridded Data-sets of SPI, Objective Drought Assessment, Free SPI-data Download.

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