Please find documentation for this dataset at the following site: http://www.cgd.ucar.edu/cas/catalog/climind/pdsi.html
Primary Reference:
Dai, A., K. E. Trenberth, and T. Qian, 2004: A global data set of Palmer Drought Severity Index for 1870-2002: Relationship with soil moisture and effects of surface warming. J. Hydrometeorology, 5, 1117-1130.
