Geoscience Reference
In-Depth Information
Recognition of the problem has brought belated remedial measures, including repairs
to the banks of the Syr Darya to reduce seepage losses and the construction of a dyke
to enable more water to remain in the northern sector of the Aral Sea (Pala,
2008
).
The success of these measures will depend on the more economical use of water and
especially on whether climate change in the headwaters of the twomain rivers will lead
to reduced flow and increased evaporation. Similar caveats apply to the recent plans
by Turkmenistan to fill the Karashkor Depression with surplus drainage water, which
may contain high levels of dissolved pesticides and herbicides (Stone,
2008
). Any
increase in climatic variability (as foreshadowed by the IPCC,
2007a
) will accelerate
human migration out of these parts of Central Asia. Creeping environmental change
in the Aral Sea Basin over the past fifty years may offer a useful analogue for the
present and future impact of climatic change in the desert world.
24.9.2 China: dune reactivation in northern China
The Desert Research Institute of the Chinese Academy of Science in Lanzhou also
has field stations at Shapotou and Yanchi and has over the years published excellent
data on the extent and severity of desertification in China (Zhu et al.,
1989
;Zhuand
Wang,
1992
; Zhu et al.,
1992
; Wang,
1993a
; Wang,
1993b
; Zhu and Wang,
1993
).
The
Atlas of Natural Disasters in China
(Zhang et al.,
1992
) provides useful additional
information. The Chinese government has long been acutely aware of the need for
desertification control (Ci,
1998
), and the increase over the past two decades in dust
storms afflicting Beijing has reinforced this perception. China's Agenda 21 (
1994
)
devotes a full chapter to desertification, and the
Beijing Review
publishes thoughtful
articles on the causes and economic impacts of desertification in China, but the
possible impacts of future climate change are perhaps insufficiently embedded in
current strategic planning, despite Chinese scholars having long been aware of the
impact of historic changes in climate on desertification in Xinjiang and further to the
east (Zhang et al.,
1991
; Xia et al.,
1993
; Xia et al.,
1995
; Zhang,
1995
).
China is unique in having the largest and thickest loess mantle of anywhere in
the world, and the highly fertile loess soils are peculiarly susceptible to accelerated
erosion, resulting in enormous volumes of sediment carried in suspension by the big
rivers draining the Loess Plateau. (As an aside, more than two-thirds of the 20 billion
(10
9
) tonnes of sediment carried each year to the world's oceans comes from five
river basins, two in China - the Yangtze and Huanghe - and the other three from the
Himalayas via India, Bangladesh and Pakistan, respectively - the Ganga, Brahmaputra
and Indus.)
The loess in China was laid down during colder, drier and windier climatic intervals
in the geologically recent past, and it became vegetated and weathered to form soils
during warmer, wetter phases when the summer monsoon was strong (
Chapter 9
). This
