This is the readme file for the self-calibrating Palmer Drought Severity Index (scPDSI) data for North America (20N-50N and 130W-60W), spanning the period 1901-2002 with monthly resolution. The spatial resolution is 0.5 x 0.5 degrees. The North-American 'window' available via these web pages is a subset of the global data. The format of the data is based on that of the CRU TS 2.1 datasets. Each gridbox is characterized with gridcoordinates (i,j), which give the position of the gridbox in a grid of size (720,360) which covers the globe. The first coordinate denotes longitude, the second coordinate latitude. Gridbox (1,1) is the gridbox *centered* at lon=179.75E and 89.75S, gridbox (720,360) is centered at lon=179.75W and 89.75N. Only gridboxes which contain data are included in this dataset (excluding gridboxes above sea or large lakes etc.) The scPDSI data for each gridbox are given as an array with 12 columns for the 12 months of the year, and 102 rows, for the years 1901 to 2002. The index values are multiplied by 100 and then rounded off to the nearest integer. When using these data, please cite: van der Schrier, G., Briffa, K. R., Osborn, T. J. and Cook, E. R. (2006) Summer moisture variability across North America, J. Geophys. Res. (Atmospheres) 111: D11102, doi:10.1029/2005JD006745 The publication which introduced the self-calibrating PDSI, and gives a large amount of detailed information about its calculation, is: Wells, N., Goddard, S. and Hayes, M. J. (2004) A Self-Calibrating Palmer Drought Severity Index, J. Climate 17:2335-2351 Gerard van der Schrier acknowledges support of the UK Natural Environment Research Council (NERC) through the RAPID Climate Change programme (grant NER/T/S/2002/00440). Keith R. Briffa and Tim J. Osborn also acknowledge support from the EU project SOAP.