Global - Standardised Precipitation - Evapotranspiration Index - Spanish National Research Council

The Global SPEI database, SPEIbase, offers long-time, robust information about drought conditions at the global scale, with a 0.5 degrees spatial resolution and a monthly time resolution. It has a multi-scale character, providing SPEI time-scales between 1 and 48 months. Currently, it covers the period between January 1901 and December 2015.

The SPEIbase consists of standardized values over the emerged land pixels. No land pixels are assigned a value of 1.0x10^30. In some rare cases it was not possible to achieve a good fit to the log-logistic distribution, resulting in a NAN (not a number) value in the database.

The SPEIbase is based on the FAO-56 Penman-Monteith estimation of potential evapotranspiration. This is a major difference with respect to the SPEI Global Drought Monitor, that uses the Thornthwaite PET estimation. The Penman-Monteith method is considered a superior method, so the SPEIbase is recommended for most uses including long-term climatological analysis.