The impact ofclimate change onfresh water resources 163Desertification
Drylands (defined as those areas where precipitation is low and where
rainfall typically consists of small, erratic, short, high-intensity storms)
cover about forty per cent of the total land area of the world and support
over one-fifth of the world’s population. Figure 7.9 shows how these arid
areas are distributed over the continents.
Desertification in these drylands is the degradation of land brought
about by climate variations or human activities that have led to decreased
vegetation, reduction of available water, reduction of crop yields and ero-
sion of soil. The United Nations Convention to Combat Desertification
(UNCCD) set up in 1996 estimates that over seventy per cent of these
drylands,covering over twenty-five per cent of the world’s landarea, are
degraded^33 and therefore affected by desertification. The degradation can
be exacerbated by excessive land use or increased human needs (gener-
ally because of increased population), or political or economic pressures
(for instance, theneed to grow cash crops to raiseforeign currency). It
is often triggered or intensified by a naturally occurring drought.
The progress of desertification in some of the drylands will be in-
creased by the more frequent or more intense droughts that are likely to
result from climate change during the twenty-first century.
Figure 7.9The world’s drylands, by continent. The total area of
drylands is about sixty million square kilometres (about forty per cent of
the total land area), of which ten million are hyper-arid deserts.