The human ecology of climate change - Climate Change: Biological and Human Aspects - page 417

counterparts typically used for climate simulations. They also used a river run-off
model as that is a better predictor of flooding (the inability to drain land) than precip-
itation and used actual precipitation data from the autumns between 1958 and 2001.
They concluded that whereas the precise magnitude of the anthropogenic contribution
remained uncertain, in nine out of ten cases their results indicate that 20th-century
anthropogenic greenhouse gas emissions increased the risk of floods occurring in
England and Wales in the autumn of 2000 by more than 20%, and in two out of
three cases by more than 90%. Together these two papers indicate that the frequency
of intense rainfall events is likely to increase with global warming. (See also an
accompanying review article by Richard Allan, 2011.)
Finally, increased major floods could well happen in the summer despite European
summers becoming drier. Seemingly paradoxically, computer models predict an
increase in intense summer rainfall with global warming. Instead of the lower rainfall
being spread across summer months, there will be a tendency for this precipitation
to clump into extreme weather events (Christensen and Christensen, 2002). This is
because in a warmer world there is more water vapour in the air. Of course, some air is
warmer than other air. When water-laden air (more than is historically anticipated at a
given latitude) meets cool air the resulting rainfall will be greater. Additionally, mat-
ters can even be worse. Consider two bodies of warm, water-laden air colliding. There
is nowhere for the air to go but up. At a higher altitude it cools, again releasing water
but even more than in the previous scenario. The consequence of this for flooding
is significant. If rainfall is spaced out over weeks then the water has the opportunity
to sink into the ground and then into the subsurface geology. If a few weeks' or
even a month's worth of rain falls at once, due to such an atmospheric collision, then
there is no time for the resulting precipitation to drain away and so it remains on the
surface. Problems are compounded if the surface is corrugated with hills and valleys,
as this volume of rain will run off the hills into the valleys as fast-flowing floods.
Of course, there are parts of the Earth's surface that historically are warmer than
temperate latitudes and which also have high rainfall. However, these regions have
waterways gouged out by previous rainfall and if they are inhabited the appropriate
drainage systems are in place. With climate change, a place that previously only
had moderate, well-spaced rain with time becomes exposed to more extreme rainfall
regimens; there will not be appropriate drainage systems in place and so flooding
results, with property damage and possible loss of life.
Flooding from both sea-level rise and increased precipitation from greater marine
evaporation in a warmer planet are expected symptoms of global warming, and this
is stated by the IPCC. The UK government's Foresight report, Migration and Global
Environmental Change (Vafeidis et al., 2011), estimated that in the year 2000 there
were some 628 753 970 people (more than 10% of the then global population) in
low-lying coastal areas less than 10 m above sea-level: the areas of land prone to both
rain-fed flooding and sea-level rise. More than 23% of these were urban dwellers.
Table 7.1 lists the population living in such low-elevation coastal zones (LECZs) in
selected countries. It is expected that these numbers will rise with population growth
in the 21st century.
However, the opposite of an excess of water, drought, is paradoxically also a prob-
lem and is also likely in other areas of a warmer world that have greater evaporation