Abstract:
(from: Cook, et al. Long-Term Aridity Changes in the Western United States
Science, Vol. 306, No. 5698, pp. 1015-1018, 5 November 2004.) The western
United States is experiencing a severe multi-year drought that is unprecedented
in some hydroclimatic records. Using gridded drought reconstructions that cover
most of the western US over the past 1,200 years, we show that this drought
pales in
... comparison to an earlier period of elevated aridity and epic drought
in AD 900-1300, an interval broadly consistent with the "Medieval Warm Period".
If elevated aridity in the western US is a natural response to climate warming,
then any trend towards warmer temperatures in the future could lead to a
serious long-term increase in aridity over western North America.
See: http://www.ncdc.noaa.gov/paleo/pubs/cook2004/cook2004.html
These data sets contain the information for all 286 grid-points in one large
matrix. There is a matrix for RECS (summer PDSI reconstructions), NCRNS (number
of chronologies in each reconstruction), CRSQ (Calibration R-SQuare), VRSQ
(verification period r-square), RE (Verification reduction of error), and CE
(Verification coefficient of efficiency) , with the beginning year being -1 and
the outer year 2003 in every case. For the ACT (actual summer PDSI data updated
to 2003 for the US part of the grid) file, all data begin in 1900. 
