Geoscience Reference
In-Depth Information
logistically a simple operation now perfected by years of investigation in places like
Northwest China and in Iran. The benefit/cost ratio of planting is low or negative.
But planting is visible and gives the impression that something is being done. It
allows government agencies to avoid tackling the much harder social and economic
problems of insidious land degradation. Phenomena like desertification involve
environmental, economic and social factors The combined effects have either been
ignored or treated in a one-sided manner. Progress in combating desertification
will require a major re-think (Carrad et al. 2006 ) and the application of holistic
approaches such as Integrated Ecosystem Management.
Land degradation means reduction or loss of the biological or economic produc-
tivity and complexity of rain fed cropland, irrigated cropland, or range, pasture,
forest and woodlands resulting from land use or from a process or combination
of processes, including processes arising from human activities and habitation
patterns, such as soil erosion caused by wind and/or water; deterioration of the
physical, chemical and biological or economic properties of soil; and long-term
loss of natural vegetation.
Arid, semi-arid and dry sub-humid areas means areas, other than polar and
sub-polar regions, in which the ratio of annual precipitation to potential evapo-
transpiration falls within the range from 0.05 to 0.65 . Hyper-arid areas, including
real deserts such as the Sahara and China's Taklamakan were excluded from the
official UN definition. Their inclusion in the areas of so-called desertified land in
China and in some other countries like Oman, Egypt and Libya has been a source
of confusion (Squires et al. 2011 ).
3
China Deserts
3.1
Characteristics of China Deserts
They cover a large area, 2.674 million km 2 , which is 30 % of the land area
(Fig. 1.2 ). Climatic conditions are characterized by dry air and lack of rainfall.
Annual precipitation is less than 200 mm and sometimes there is no rain at all. Due
to lack of the moisture in the air, the difference of the diurnal temperature is high
(reaching 30 ı C). The rate of transpiration rate exceeds the rate of precipitation. It
is severely cold and dry in the high altitude areas (Fig. 1.1 ).
China's total amount of water resources is estimated at 2.8 trillion cubic meters
(m 3 ), and 200 m 3 per capita, only one-fourth of the world's average. China is divided
into four zones in terms of natural rainfall. Firstly, the rain abundant zone, located
to the south of Qilian Mts and the Yellow River (Huanghe) where precipitation is
between 800 and 1,600 mm; secondly, the sub-humid area with a rainfall between
400 and 800 mm located to the north of. Qilian Mts. and the Huanghe basin; thirdly,
the semi-arid zone with a rainfall ranging from 200 to 400 mm and fourthly, the
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