10
1 Physical Settings and Water Challenges
resource zone has the second greatest runoff, with 815.7 mm; and the least annual
runoff occurs in the rivers of northwest China, with only 34.9 mm.
The inter-year runoff variation mainly depends on precipitation changes and is
influenced by factors such as runoff recharge, catchment size, and landscape. The
runoff in China has large inter-year variations, larger in northern China than in
southern China and larger in arid areas than in humid areas. The ratio of the maximum
annual runoff to the minimum annual runoff is generally less than 5:1 in the southern
part of the country and more than 10:1 in the northern part. The Cv of runoff is mostly
above 0.5 in the Liao, Hai, and Huai River Basins, 0.2–0.4 in the Yellow River and
Songhua River Basins, 0.15 in the Yangtze River and rivers in Southwest China, and
0.2–0.3 in the rivers in the Southeast and the Pearl River basin. In Northwest China,
the Cv in rivers recharged by glaciers and snowmelt is generally below 0.25, while
in rivers replenished by precipitation it is generally 0.3–0.7.
The river runoff in China happens mostly in the summer and is higher in northern
China. The ratio of the maximum consecutive-4-month runoff to annual runoff in
northern China is generally 60–80%, although some hydrological stations in the
Hai River Basin and the Yellow River Basin have exceeded 80%, and some stations
in Northwest China have reached 90%. The ratio in Southern China is 50–70%,
generally, and for the rivers in Southeast China it is only about 55%.
As for the transboundary rivers, according to the 1956–2000 hydrological series,
the runoff inflowing to China is 21.4 km
3 , mostly in the Pearl River and the rivers in
Northwest China. The outbound runoff is 727.88 km
3 , of which the runoff crossing
the border and flowing into other countries is 597.45 km
3 and that flowing into the
boundary rivers is 130.43 km
3 (Table 1.4).
The annual average runoff to the sea is 1,672.55 km
3 . The Yangtze River Basin
contributes 919.2 km
3 of this, or 55% of the total. The Hai River Basin contributes
only 10.13 km
3 (Table 1.5). The change of runoff into the sea is affected by both
natural and human factors, such as precipitation and water resource development. The
Yellow River, the Huai River, the Hai River, and the Liao River have had a significant
decrease in runoff into the sea due to increasing water resource development and use
since the 1950s, particularly the Yellow and Hai Rivers.
Water budget analysis shows that the values of hydrological elements and runoff
coefficients are quite different between the outflowing area and the inland river basins,
and also between the southern part and the northern part of the outflowing area.
The depth of annual mean precipitation in the outflowing area of southern China is
1,204 mm, of which 46% is consumed in the form of land surface evaporation, and
54% contributes to river runoff. As for the outflowing area in northern China, the
depth of annual mean precipitation is 546 mm, of which only 23% forms river runoff
and 77% is consumed in the form of land surface evaporation. The depth of mean
annual precipitation in the inland river basins is only 154 mm, of which 79% is lost in
evaporation; the annual runoff depth is only 32 mm, and there is a large area without
runoff. The mean runoff coefficient for the whole country is 0.44, which means 44%
of China’s precipitation forms runoff.
1 Physical Settings and Water Challenges
resource zone has the second greatest runoff, with 815.7 mm; and the least annual
runoff occurs in the rivers of northwest China, with only 34.9 mm.
The inter-year runoff variation mainly depends on precipitation changes and is
influenced by factors such as runoff recharge, catchment size, and landscape. The
runoff in China has large inter-year variations, larger in northern China than in
southern China and larger in arid areas than in humid areas. The ratio of the maximum
annual runoff to the minimum annual runoff is generally less than 5:1 in the southern
part of the country and more than 10:1 in the northern part. The Cv of runoff is mostly
above 0.5 in the Liao, Hai, and Huai River Basins, 0.2–0.4 in the Yellow River and
Songhua River Basins, 0.15 in the Yangtze River and rivers in Southwest China, and
0.2–0.3 in the rivers in the Southeast and the Pearl River basin. In Northwest China,
the Cv in rivers recharged by glaciers and snowmelt is generally below 0.25, while
in rivers replenished by precipitation it is generally 0.3–0.7.
The river runoff in China happens mostly in the summer and is higher in northern
China. The ratio of the maximum consecutive-4-month runoff to annual runoff in
northern China is generally 60–80%, although some hydrological stations in the
Hai River Basin and the Yellow River Basin have exceeded 80%, and some stations
in Northwest China have reached 90%. The ratio in Southern China is 50–70%,
generally, and for the rivers in Southeast China it is only about 55%.
As for the transboundary rivers, according to the 1956–2000 hydrological series,
the runoff inflowing to China is 21.4 km
3 , mostly in the Pearl River and the rivers in
Northwest China. The outbound runoff is 727.88 km
3 , of which the runoff crossing
the border and flowing into other countries is 597.45 km
3 and that flowing into the
boundary rivers is 130.43 km
3 (Table 1.4).
The annual average runoff to the sea is 1,672.55 km
3 . The Yangtze River Basin
contributes 919.2 km
3 of this, or 55% of the total. The Hai River Basin contributes
only 10.13 km
3 (Table 1.5). The change of runoff into the sea is affected by both
natural and human factors, such as precipitation and water resource development. The
Yellow River, the Huai River, the Hai River, and the Liao River have had a significant
decrease in runoff into the sea due to increasing water resource development and use
since the 1950s, particularly the Yellow and Hai Rivers.
Water budget analysis shows that the values of hydrological elements and runoff
coefficients are quite different between the outflowing area and the inland river basins,
and also between the southern part and the northern part of the outflowing area.
The depth of annual mean precipitation in the outflowing area of southern China is
1,204 mm, of which 46% is consumed in the form of land surface evaporation, and
54% contributes to river runoff. As for the outflowing area in northern China, the
depth of annual mean precipitation is 546 mm, of which only 23% forms river runoff
and 77% is consumed in the form of land surface evaporation. The depth of mean
annual precipitation in the inland river basins is only 154 mm, of which 79% is lost in
evaporation; the annual runoff depth is only 32 mm, and there is a large area without
runoff. The mean runoff coefficient for the whole country is 0.44, which means 44%
of China’s precipitation forms runoff.