The most
important spatial
pattern (top) of
the monthly
Palmer Drought
Severity Index
(PDSI) for 1900
to 2002.
The time series
(below) accounts
for most of the
trend in PDSI.
Drought is increasing most places
Mainly decrease in rain
over land in tropics and
subtropics, but enhanced
by increased atmospheric
demand with warming
IPCC 2007