Agriculture Reference
In-Depth Information
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Table 28.1 Area damaged by agricultural disasters in China
Total area damaged by
Drought-damaged area
Drought-damaged area as
Decade
natural hazards (10,000 ha)
(10,000 ha)
percentage of the total
1950s
2207.3
1162.1
48
1960s
3780.4
2177.4
57
1970s
4390.5
2855.5
65
1980s
4208.6
2414.1
57
1990s
4949.7
2489.2
50
So urce: State Statistical Bureau (1996).
west China and in the middle and lower reaches of Yangtze River, respec-
tively (Li and Lin, 1993).
[356
M ain Causes of Drought
The possible factors responsible for droughts in China can be categorized as
na tural and, to some extent, cultural, as described in the following sections.
Line
——
-0.1
——
Long
PgEn
N atural Factors
Meteorological Factors The main agricultural region in eastern China is
influenced by the East Asia monsoon. In this region, the distribution of
precipitation is uneven and annual variation is high. The precipitation zone
jumps between the northern and the southern parts of the country accord-
ing to a tropical high-pressure concentration during the April-September
period, resulting in such an uneven precipitation distribution that it causes
storms and floods in some regions and droughts in other regions. In addi-
tion, movement of precipitation zones also causes droughts. Lack of rains
along the Yangtze River during summer can also lead to serious droughts.
The Chinese climate is mainly controlled by four semipermanent atmo-
spheric activities: the Mongolia high pressure and the Aleutian low pressure
during winter and the India low-pressure and the Pacific tropic high pres-
sure during summer. When the Mongolia high-pressure is strong and the
Pacific tropic high pressure is weak during winter, cold air drives straight
into the south from the north, and the whole country experiences a cold air
mass. As a result, the weather turns cold and dry (because of no rains). In
summer, when the Pacific tropic high pressure and the India high pressure
are strong and active, the major part of the country is influenced by warm
and wet airflow from southeast and southwest. Consequently, rains occur
during summer. The rainy season in China is mainly from April to Septem-
ber. However, the spatial distribution of precipitation and its intensity dif-
fer from year to year depending on the timing of northward movement of
subtropical high pressure, the active range of the high pressure, and the
large annual variation in other weather systems.
The active intensity of the western Pacific tropical high pressure is re-
lated to ENSO (El Niño/Southern Oscillation; chapter 3). When the ENSO
[356
 
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