The impact ofclimate change onfresh water resources 161depends to a great degree on extreme conditions. This is well illus-
trated by looking at the scale of natural disasters involving water – either
too much water in floods or too little in droughts. Some of the most
damaging floods of recent years were mentioned in Chapter 1 (page 5)
- see also Table 7.3 (page 183). Droughts do not appear high up on the
table of natural disasters, not because they are unimportant, but because,
unlike most other disasters, their effects tend to be felt over a long per-
iod of time. The ‘dust bowl’ years in the 1930s in the United States
are still within living memory, as are the droughts and famines in India
in 1965–7 which, it is estimated, claimed one and a half million lives.
Recent decades have seen a series of damaging droughts in the Sahel
region and in other parts of Africa^28 – which are still recurring only too
frequently on that continent.
Any temperature or rainfall record shows a large variability. The
inevitable result of variability added to higher average temperatures
(meaning higher evaporation) and higher average rainfall will be a greater
number and greater intensity of both droughts and floods.^29 For instance,
associated with the substantial changes in average runoff expected by
2050 in parts of Asia mentioned above will be increases in the num-
ber and intensity of floods and droughts. Some of the areas likely to be
affected are just those areas that are particularly vulnerable at the mo-
ment – although, as was also implied in Chapter 6, droughts and floods
are increasingly likely to occur in some locations where, at present, such
disasters are rare. Very few quantitative estimates have been made of the
likely increase in floods or droughts as a result of the increase of green-
house gases. One estimate quoted in Chapter 6 (page 131) projected an
increase of a factor of five in intense precipitation events in parts of
Europe under a doubled atmospheric carbon dioxide concentration.
The monsoon regions of southeast Asia are an example of an area that
may be particularly vulnerable to both floods and droughts. Figure 7.8
shows the predicted change in summer precipitation over the Indian sub-
continent as simulated by a regional climate model (RCM) for 2050
under a scenario similar to SRES A1B. Note the improvement in detail
of the precipitation pattern that results from the use of the increased
resolution of the regional model compared with the global model
(GCM), for instance over the Western Ghats (the mountains that rise
steeply from India’s west coast) there are large increases not present
in the global model simulation. The most serious reductions in water
availability simulated by the regional model are in the arid regions of
northwest India and Pakistan where average precipitation is reduced to
less than 1 mm day−^1 – that coupled with higher temperatures leads to a
sixty per cent decline in soil moisture. Substantial increases in average
precipitation are projected for areas in eastern India and in flood-prone