Palmer Drought Severity Index (PDSI)

Main References:

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.

Dai, A., 2011a: Characteristics and trends in various forms of the Palmer Drought Severity Index (PDSI) during 1900-2008. J. Geophys. Res., 116, D12115, doi:10.1029/2010JD015541.

Dai, A., 2011b: Drought under global warming: A review. Wiley Interdisciplinary Reviews: Climate Change, 2, 45-65. DOI: 10.1002/wcc.81.   

Dai, A., 2013: Increasing drought under global warming in observations and models. Nature Climate Change, 3, 52-58. DOI: 10.1038/nclimate1633.   

Dai, A. and T. Zhao, 2016: Uncertainties in historical changes and future projections of drought. Part I: estimates of historical drought changes. Climatic Change, xx, 1-15. DOI: 10.1007/s10584-016-1705-2.   

DATA DESCRIPTION: These data consist of the monthly PDSI over global land areas computed using osberved or model monthly surface air temperature (from Jones and Moberg 2003 and updates) and precipitation (see above papers), plus other surface forcing data for the sc_PDSI_pm case.

Added Nov 10, 2016: sc_PDSI_pm data for 1900-2099 based on 14 CMIP5 models under RCP4.5 scenario are posted online at University at Albany site:

PLEASE NOTE: For our own record, we would appreciate it very much if you could email Dr. A. Dai a few lines after you download the data set to indicate your intended use of the data set. Thank you!

PDSI Data from Dai et al. (2004 &updates):

The PDSI data (binary file, text file, netCDF file) and the associated README file may be obtained by clicking on the links. To validate the data, compare the PDSI maps for January 1950 and 2002. To view the full size image, please see: PDSI EOF.

PDSI data from Dai (2011a, 2011b) (updated to 2014, same file formats as above, check README before asking questions):

Self-calibrated PDSI with Penman-Monteith PE (sc_PDSI_pm, recommended over the original PDSI) based on historical data (1850-2010 data binary file, 1850-2010 data netCDF file, 1850-2010 text file; 1850-2012 data binary file, 1850-2012 scPDSIpm data netCDF file, 1850-2012 text file, 1850-2012 scPDSIpm data netCDF file) , 1850-2014 scPDSIpm data netCDF file). See Dai (2011a) for caveats in the forcing data. A small faction (<0.08%) of the data pints are outside the (-25, 25) range in earlier versions before Nov. 2, 2015. We suggest to skip these data points in regional averaging and other analyses.   

***Update on Nov. 2, 2015: The 1850-2014 scPDSIpm data file was revised using following steps: a) a narrower raonge of -10 to +10 was imposed, b) the time series at each grid box was scaled to have the same standard deviation as over the central U.S. during the calibration period from 1950-1979, and c) small gaps were infilled using bilinear interpolation using nearby values. These new steps improve the spatial homogeneity although temporal inhomogeneity may still exist for a small number of grid boxes in northern Africa and other regions. Users should check the data series before applicaitons, especially for periods before 1950.   

***Update on Feb. 24, 2016: The 1850-2014 scPDSIpm data file was revised with slight changes from the previous version of Nov.2, 2015. Users are advised to update their applications with this updated version.


EOFs for PDSI 1900 through 2002

Temporal (left, black) and spatial (right) patterns of the two leading EOFs of the monthly PDSI (normalized by its standard deviation prior to the EOF analysis). Red (blue) areas are dry (wet) for a positive temporal coefficient. Also shown in the left-lower panel (red) is the Darwin mean sea level pressure shifted to the right by six months to obtain the maximum correlation (r=0.62). Variations on < 2 year time scales were filtered out in the left panels. The percentage variance explained is shown on the top of the left panels. (From Dai et al. 2004)



  • Chen, M., P. Xie, J.E. Janowiak, and P.A. Arkin, 2002: Global land precipitation: a 50-yr monthly analysis based on gauge observations. J. Hydrometeorol., 3, 249-266.
  • Dai, A., I. Fung, and A. D. Del Genio, 1997: Surface observed global land precipitation variations during 1900-1988. J. Climate, 10, 2943-2962. [pdf]
  • Dai, A., K. E. Trenberth, and T. Karl, 1998: Global variations in droughts and wet spells: 1900-1995. Geophys. Res. Lett., 25, 3367-3370. [pdf]
  • 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. Hydrometeorol., 5, 1117-1130. [pdf]
  • Jones, P.D., and A. Moberg, 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001. J. Climate, 16, 206-223.
  • Palmer, W. C, 1965: Meteorological Drought. Res. Paper No.45, 58pp., Dept. of Commerce, Washington, D.C.
  • Webb, R. S., C. E. Rosenzweig, and E. R. Levine, 1993: Specifying land surface characteristics in general circulation models: soil profile dataset and derived water-holding capacities. Global Biogeochem. Cycles, 7, 97-108.

Old PDSI webpage.