Modeling the Recent Evolution of Global Drought and Projections for the
Twenty-First Century with the Hadley Centre Climate Model
Hadley Centre for Climate Prediction and
Research, Met Office, Exeter, United Kingdom

Sample quote: ” … the proportion of the land
surface in extreme drought is predicted to
increase from 1% for the present day to 30% by
the end of the twenty-first century.”

Meteorological drought in the Hadley Centre
global climate model is assessed using the Palmer
Drought Severity Index (PDSI), a commonly used
drought index. At interannual time scales, for
the majority of the land surface, the model
captures the observed relationship between the El
Niño-Southern Oscillation and regions of relative
wetness and dryness represented by high and low
values of the PDSI respectively. At decadal time
scales, on a global basis, the model reproduces
the observed drying trend (decreasing PDSI) since
1952. An optimal detection analysis shows that
there is a significant influence of anthropogenic
emissions of greenhouse gasses and sulphate
aerosols in the production of this drying trend.
On a regional basis, the specific regions of
wetting and drying are not always accurately
simulated. In this paper, present-day drought
events are defined as continuous time periods
where the PDSI is less than the 20th percentile
of the PDSI distribution between 1952 and 1998
(i.e., on average 20% of the land surface is in
drought at any one time). Overall, the model
predicts slightly less frequent but longer events
than are observed. Future projections of drought
in the twenty-first century made using the
Special Report on Emissions Scenarios (SRES) A2
emission scenario show regions of strong wetting
and drying with a net overall global drying
trend. For example, the proportion of the land
surface in extreme drought is predicted to
increase from 1% for the present day to 30% by
the end of the twenty-first century.

13 AUGUST 2004
VOL 305

More Intense,More Frequent, and Longer Lasting
Heat Waves in the 21st Century
Gerald A.Meehl and Claudia Tebaldi


A global coupled climate model shows that there
is a distinct geographic pattern to future
changes in heat waves.  Model results for areas
of Europe and North America,  associated with the
severe heat waves in Chicago in 1995 and Paris in
2003, show that future heat waves in these areas
will become more intense,  more frequent,  and
longer lasting in the second half of the 21st
century.  Observations and the model show that
present-day heat waves over Europe and North
America coincide with a specific atmospheric
circulation pattern that is intensified by
ongoing increases in greenhouse gases, indicating
that it will produce more severe heat waves in
those regions in the future.


” Å  areas already experiencing strong heat waves
(e.g., southwest, midwest, and southeast United
States and the Mediterranean region) could
experience even more intense heat waves in the
future. But other areas (e.g., northwest United
States, France, Germany, and the Balkans) could
see increases of heat wave intensity that could
have more serious impacts because these areas are
not currently as well adapted to heat waves.”

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