Geoscience Reference
In-Depth Information
dunes is underway, and a useful start has been made at the Shu Gui Desert Control
Station, although tree losses from insect pests and groundwater salinity had been
substantial. Control of desertification along the Yellow River is an important element
of China's national plans to combat desertification (China's Agenda 21,
1994
, p. 189).
Overgrazing and dune reactivation are the prime causes of the present massive influx
of sand into the Yellow River, but unless upstream abstraction of water for irrigation
is curtailed, the silting up of the river will inevitably become worse.
If rainfall in northern China becomes more erratic than it is already (Ye et al.,
1987
;
Domros and Peng,
1988
), as the IPCC forecasts suggest (IPCC,
2007a
; IPCC,
2007b
;
IPCC,
2007c
), there is likely to be further movement of people and livestock into
areas perceived as underpopulated, with concomitant destruction of the plant cover
and reactivation of the still vast areas of fixed dunes. In northern Xinjiang, many of the
farmers harvest meltwater from the snow-capped Tian Shan ranges for irrigating their
fruit and vegetable plots. As warming proceeds, the ablation of snow in summer will
exceed winter accumulation, glaciers will continue to retreat and the reliable supplies
of irrigation water from springtime snow-melt will diminish.
Any reduction in plant cover in semi-arid or seasonally wet tropical areas leads to
a dramatic increase in sediment loss, with concomitant loss of arable land, pasture
and woodland resources and often massive sedimentation problems downstream, as
in the case of the Loess Plateau of China and the Huanghe, or Yellow River. Human
migration from areas of high to low population density in parts of northern China since
the 1950s has had a discernible and severe impact on the soils and plant cover, which
has led to an increase in sand and dust storms. It is as yet hard to foresee whether
these conditions will become more widespread throughout the region.
24.10 Desertification in Africa: an example from Ethiopia
The recurrent twentieth-century droughts in Africa caused widespread social distress,
famine and migration, and proved to be the catalyst for the Desertification Convention
discussed in
Section 24.11
. The droughts and famines in Ethiopia in particular have
attracted considerable media attention, and the widespread political unrest generated
by recurrent famines in the 1970s and early 1980s helped bring to an end the long
reign of the Emperor Haile Selassie and that of the military dictator Haile Mariam
Mengistu. Ethiopia is well-endowed with fertile volcanic soils and with large perennial
rivers, so at first blush it seems strange that famines are so frequent. One reason that
is often advanced for the low crop yields obtained by many farmers is indiscriminate
deforestation and accelerated soil erosion. How valid is this perception?
It certainly seems true that in the Ethiopian Semien Mountains National Park, the
area of natural forest declined from 56 per cent to 22 per cent within forty years
(Hurni,
1999
). Clive Nicol, the first game warden appointed by the Imperial Ethiopian
Government to manage the park, found that he faced an impossible task in seeking
