Geoscience Reference
In-Depth Information
24.13 Conclusion
A persistent problem in assessing the causes of desertification arises from the fact
that it is often very hard to separate out the effects of climatic variability from
those of human activities. However, the three examples discussed in some detail for
Australia, China and Ethiopia indicate very clearly that overenthusiastic removal of
the vegetation cover can lead to severe and widespread forms of land degradation,
ranging from rising saline groundwater (Australia) to dune reactivation (northern
China) to accelerated soil erosion (Ethiopian Highlands). In addition, the effects of
such deforestation/removal of the plant cover can extend well outside the original
area, leading to choking of rivers with sediment and siltation of reservoirs hundreds
of kilometres downstream.
Analysis of the causes of land degradation processes reveals a complex web of
interactions in which social and economic factors are often at least as important as
purely biophysical factors. Looking to the future, those areas now most vulnerable to
interannual climatic variability will continue to be the arid and semi-arid areas, but the
seasonally wet tropics and the dry subhumid regions that now receive 1,500-750 mm
of rain a year will become increasingly sensitive to any future changes in temperature,
evaporation and precipitation, as discussed in
Chapter 25
. Analysis of the causes
and consequences of desertification processes related to both climatic variations and
human activities suggests that human migration within and into these regions can
seriously aggravate existing problems of land degradation.
Biomass burning in the seasonally wet tropics, notably the dry subhumid regions
already severe during dry years, is generating health problems, aggravating soil erosion
and has the potential to change regional climate. In addition, in the absence of univer-
sally accepted criteria to define the extent and severity of desertification processes,
it is difficult to monitor current trends within the drylands of the world. Finally, the
success or otherwise of the many measures designed to reduce or prevent desertific-
ation is seldom publicised, so that it is often hard to determine the degree of success
of prevention and rehabilitation strategies.
