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1 Physical Settings and Water Challenges
1.2.2 Evaporation
1.2.2.1 Potential Evaporation
The annual average potential evaporation (approximately used by an E601 evaporating dish) is higher in western China than in eastern China and is generally higher in
the plains than in the mountainous areas. The lowest annual average potential evaporation is in northeast Heilongjiang Province, at only about 500 mm; the highest
value appears in northwestern Inner Mongolia, where it is as high as 2,600 mm. The
lower value regions, with less than 800 mm, are the Erguna, the Songhua River, the
Yalujiang River, and the middle and lower reaches of the Yangtze River, covering
22% of the country’s land area. The higher value regions, with more than 1,200 mm,
accounting for 33% of the national area, are the plains and river basins in Northwest
China, the Qinghai–Tibet Plateau, and the hot and dry valleys in middle and western
Yunan Province. Other regions, including most of the plain in Northeast China, the
Hai River, the Huai River, the middle and lower reaches of the Yellow River, parts
of the upper and lower reaches of the Yangtze River, the middle and lower reaches
of the Pearl River, most of the rivers in Southwest China, and the eastern part of
the Qinghai–Tibet Plateau, generally have annual average potential evaporation of
between 800 and 1,200 mm. These regions account for about 45% of land area of
the country.
The seasonal variation of potential evaporation in China is striking. The annual
variation of potential evaporation and its regional differences are smaller than those of
precipitation, with larger changes in northern China. The Cv of potential evaporation
varies from 0.07 to 0.18. The ratio of annual maximum and minimum potential
evaporation is 1.3–1.9.
1.2.2.2 Real Evaporation
The annual average real evaporation for the country was 356.9 mm from 1980 to
2000, equivalent to 32% of the annual average potential evaporation and accounting
for 55.0% of the annual average precipitation. Northern China averaged 253 mm,
representing 21% of its potential evaporation and 77% of its precipitation. Southern
China was 540 mm on average, 58% of the potential evaporation, and 44% of the
precipitation (Table 1.3).
1 Physical Settings and Water Challenges
1.2.2 Evaporation
1.2.2.1 Potential Evaporation
The annual average potential evaporation (approximately used by an E601 evaporating dish) is higher in western China than in eastern China and is generally higher in
the plains than in the mountainous areas. The lowest annual average potential evaporation is in northeast Heilongjiang Province, at only about 500 mm; the highest
value appears in northwestern Inner Mongolia, where it is as high as 2,600 mm. The
lower value regions, with less than 800 mm, are the Erguna, the Songhua River, the
Yalujiang River, and the middle and lower reaches of the Yangtze River, covering
22% of the country’s land area. The higher value regions, with more than 1,200 mm,
accounting for 33% of the national area, are the plains and river basins in Northwest
China, the Qinghai–Tibet Plateau, and the hot and dry valleys in middle and western
Yunan Province. Other regions, including most of the plain in Northeast China, the
Hai River, the Huai River, the middle and lower reaches of the Yellow River, parts
of the upper and lower reaches of the Yangtze River, the middle and lower reaches
of the Pearl River, most of the rivers in Southwest China, and the eastern part of
the Qinghai–Tibet Plateau, generally have annual average potential evaporation of
between 800 and 1,200 mm. These regions account for about 45% of land area of
the country.
The seasonal variation of potential evaporation in China is striking. The annual
variation of potential evaporation and its regional differences are smaller than those of
precipitation, with larger changes in northern China. The Cv of potential evaporation
varies from 0.07 to 0.18. The ratio of annual maximum and minimum potential
evaporation is 1.3–1.9.
1.2.2.2 Real Evaporation
The annual average real evaporation for the country was 356.9 mm from 1980 to
2000, equivalent to 32% of the annual average potential evaporation and accounting
for 55.0% of the annual average precipitation. Northern China averaged 253 mm,
representing 21% of its potential evaporation and 77% of its precipitation. Southern
China was 540 mm on average, 58% of the potential evaporation, and 44% of the
precipitation (Table 1.3).