ENB:04:11
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UNESCO:
Habib Zebidi, Programme Specialist in Hydrology,
Division of Water Sciences, discussed the effects of
desertification on surface water and groundwater systems and on
water availability and quality. He began with definitions of
desertification and noted the fact that there are 6,100 million
hectares of arid lands, home to one-fifth of the world's
population, with Africa, the Arabian Peninsula and Australia as
the regions most affected. He focussed on the characteristics of
these areas. The first characteristic is that rainfall is limited
and irregular, with the greatest variability of rainfall found in
arid and semi-arid land. High sediment transport is a feature of
surface flow, due to run-off fluctuations. Another characteristic
is that groundwater is often found in these regions. The
availability of water depends on the type of catchment system
used. He noted the effects of desertification on groundwater
systems. He also discussed surface run-off from flood waters and
rain and the collection of this water with dams. He concluded by
noting the potential for conflict over water resources in the
event of drought and the need for national policies to distribute
scare water resources. He also noted the possibilities of more
violent flash floods due to the soil's lower retention capacity
to absorb irregular rainfall.