PDSI consists of global maps of monthly self-calibrating Palmer Drought Severity Index (scPDSI)
which have been calculated for selected periods of time based on the CRU TS data sets. The PDSI datasets are produced by KMNI in partnership with the Climatic Research Unit (CRU) at the University of East Anglia.

The Palmer Drought Severity Index (PDSI) is a measure of soil moisture availability that has been used extensively to study droughts and wet spells in the contiguous USA and elsewhere, particularly as the primary indicator of the severity and extent of recent droughts. Recently, the PDSI has become more popular as a drought metric in studies quantifying possible trends in future soil moisture availability and it has been used as the basis for reconstructing past variations in drought.