1.2 Hydrology
7
the mountains and less in the plains. The annual average precipitation in southern
China is 1,214.4 mm, with a corresponding volume of 4,190.0 km
3 , accounting
for 67.8% of the national total although southern China comprises only 36% of the
country’s land area. The annual average precipitation in northern China is 328.2 mm,
with a corresponding volume of 1,987.5 km
3 , accounting for 32.2% of the national
total and falling on 64% of the land. The annual average precipitation in the mountains
is 770.2 mm and accounts for 85.2% of the national total, which in the plains is
342.7 mm, or 14.8% of the national total.
Regionally, the precipitation in the country generally diminishes from southeast
to northeast. In the coastal areas of the southeastern part of the country and in some
regions of Southwest China, the mean annual precipitation is more than 2,000 mm,
while in some places near the eastern sector of the China–India boundary the annual
precipitation may be more than 5,000 mm. The annual precipitation depths for other
regions are as follows: more than 1,000 mm in the regions to the south of the middle
and lower reaches of the Yangtze River; 800–900 mm in the regions of the Qinling
and Huai River Basin; and 400–800 mm in the North China Plain, Northeast China,
the majority of Shanxi and Shaanxi Provinces, Gansu Province, the southeast part of
Sichuan Province, and the eastern part of Tibet. The western part of Northeast China,
Inner Mongolia, and the vast area to the west of Gansu Province receive less than
400 mm, and some other places receive less than 200 mm. The annual precipitation
on the western ridge of Tianshan Mountain is more than 800 mm.
Affected by the monsoon, the annual precipitation changes, as well as these
changes among regions, are significant, and even more in northern China. The annual
coefficient of variation (Cv) of precipitation from the Qilian Mountains, Qinling
Mountains, and Huai River to the south of Yimeng Mountain is less than 0.25, and it
is less than 0.20 in Southwest China. The Cv in North China is mostly greater than
0.30, and it is more than 0.40 in some areas. The Cv in Northeast China is generally
around 0.30. In most parts of Northwest China, the Cv is above 0.40, including the
Tarim, Qaidam, and Zhungeer Basins, where it exceeds 0.60. The ratio between the
maximum and minimum annual precipitation is generally 2–3, and up to 4 or more
in some areas in southern China. The ratio is less than 2.5 in southwest China, 3–6
in northern China, and highest in northwest China at more than 10.
The seasonal distribution of precipitation in China is also uneven. Except for some
small areas, the most precipitation occurs in summer, mainly in the form of storms.
Except for the northeast part of Taiwan, the least precipitation occurs in winter. In
spring and autumn, the volume of precipitation is between that in summer and winter,
but it varies from place to place. In some places, the rainfall in spring is greater than
that in autumn, and in other places the opposite is true. The ratio of the maximum
consecutive-4-month precipitation to the annual is 0.6–0.8 in most regions, higher in
the north, and lower in the south. The minimum consecutive-3-month precipitation
for most regions occurs from December to February. In southern China, the minimum
consecutive-3-month precipitation makes up 10% of the annual precipitation, but in
northern China it comprises only 5% of the annual.
7
the mountains and less in the plains. The annual average precipitation in southern
China is 1,214.4 mm, with a corresponding volume of 4,190.0 km
3 , accounting
for 67.8% of the national total although southern China comprises only 36% of the
country’s land area. The annual average precipitation in northern China is 328.2 mm,
with a corresponding volume of 1,987.5 km
3 , accounting for 32.2% of the national
total and falling on 64% of the land. The annual average precipitation in the mountains
is 770.2 mm and accounts for 85.2% of the national total, which in the plains is
342.7 mm, or 14.8% of the national total.
Regionally, the precipitation in the country generally diminishes from southeast
to northeast. In the coastal areas of the southeastern part of the country and in some
regions of Southwest China, the mean annual precipitation is more than 2,000 mm,
while in some places near the eastern sector of the China–India boundary the annual
precipitation may be more than 5,000 mm. The annual precipitation depths for other
regions are as follows: more than 1,000 mm in the regions to the south of the middle
and lower reaches of the Yangtze River; 800–900 mm in the regions of the Qinling
and Huai River Basin; and 400–800 mm in the North China Plain, Northeast China,
the majority of Shanxi and Shaanxi Provinces, Gansu Province, the southeast part of
Sichuan Province, and the eastern part of Tibet. The western part of Northeast China,
Inner Mongolia, and the vast area to the west of Gansu Province receive less than
400 mm, and some other places receive less than 200 mm. The annual precipitation
on the western ridge of Tianshan Mountain is more than 800 mm.
Affected by the monsoon, the annual precipitation changes, as well as these
changes among regions, are significant, and even more in northern China. The annual
coefficient of variation (Cv) of precipitation from the Qilian Mountains, Qinling
Mountains, and Huai River to the south of Yimeng Mountain is less than 0.25, and it
is less than 0.20 in Southwest China. The Cv in North China is mostly greater than
0.30, and it is more than 0.40 in some areas. The Cv in Northeast China is generally
around 0.30. In most parts of Northwest China, the Cv is above 0.40, including the
Tarim, Qaidam, and Zhungeer Basins, where it exceeds 0.60. The ratio between the
maximum and minimum annual precipitation is generally 2–3, and up to 4 or more
in some areas in southern China. The ratio is less than 2.5 in southwest China, 3–6
in northern China, and highest in northwest China at more than 10.
The seasonal distribution of precipitation in China is also uneven. Except for some
small areas, the most precipitation occurs in summer, mainly in the form of storms.
Except for the northeast part of Taiwan, the least precipitation occurs in winter. In
spring and autumn, the volume of precipitation is between that in summer and winter,
but it varies from place to place. In some places, the rainfall in spring is greater than
that in autumn, and in other places the opposite is true. The ratio of the maximum
consecutive-4-month precipitation to the annual is 0.6–0.8 in most regions, higher in
the north, and lower in the south. The minimum consecutive-3-month precipitation
for most regions occurs from December to February. In southern China, the minimum
consecutive-3-month precipitation makes up 10% of the annual precipitation, but in
northern China it comprises only 5% of the annual.