Standardised Precipitation Evapotranspiration Index
The Standardized Precipitation Evapotranspiration Index (SPEI) is a multiscalar Drought index based on climatic data. It Developed by Vicente-Serrano et al. (2010) at the Institute Pirenaico de Ecologia in Zaragoza, Spain. It can be used for determining the onset, duration and magnitude of drought conditions with respect to normal conditions in a variety of natural and managed systems such as crops, ecosystems, rivers, water resources, etc. See also
 Keetch–Byram drought index
 palmer drought Index
 Drought

References

External links 
 SPEI world database, updated monthly
 R package that calculates the SPEI

Meteorological indices
Droughts
Hydrology