This is the readme file for the self-calibrating Palmer Drought Severity Index
(scPDSI) data based on 22 early instrumental records for precipitation and temperature.
Based on these long scPDSI records, a gridded dataset, with spatial resolution of 5 x 5 
degrees is made which is provided as well. This gridded dataset spans the period from
1750 onwards and covers a large part of west and central Europe.

Both the long scPDSI station timeseries and the gridded dataset have a monthly temporal resolution.

The format of the long scPDSI timeseries is the year followed by 12 monthly scPDSI values.

The format of the gridded data is based on that of the gridded CRU datasets. Each gridbox
is characterized with gridcoordinates (lon - lat). The first coordinate denotes
longitude, the second coordinate latitude of the *centre* of the gridbox. 
Only gridboxes which contain data are included in this dataset (land gridboxes only)
The scPDSI data for each gridbox are given as an array with 12 columns for the 12 months
of the year. The rows correspond to the years, starting with 1750. The index values are
multiplied by 100 and then rounded off to the nearest integer. Details of the gridding
procedure and a discussion of the results can be found in the publication below.

When using these data, please cite:
Briffa KR, van der Schrier G and Jones PD (2009)
Wet and dry summers in Europe since 1750: evidence of increasing drought.
International Journal of Climatology 29, 1894-1905 (DOI: 10.1002/joc.1836).

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.

Alternatively, you can find a more concise introduction to the  self-calibrating Palmer
Drought Severity Index in:
van der Schrier G, Briffa KR, Jones PD and Osborn TJ (2006)
Summer moisture variability across Europe, J. Climate 19, 2828-2834.

Keith R. Briffa acknowledges support from UK NERC (NER/T/S/2002/00440).
Gerard van der Schrier acknowledges support from the Royal Netherlands Meteorological
Institute and the Netherlands Organization for Scientific Research (NWO) through the
combined UK-NL RAPID Climate Change programme.
Phil D. Jones acknowledges support from the US dept. Energy (Grant DE-FG02-98ER62601).