What are the characteristics of water balance and water cycle at Chinese mainland and regional scales?

Water Balance and Water Cycle in Chinese mainland Scale

Chinese mainland is located in East Asia. Due to geographical latitude, land and sea distribution, topography and atmospheric circulation, it has distinct characteristics in water balance and water cycle.

The total water vapor transport field in Chinese mainland is mainly composed of three water vapor streams, namely, the northwest water vapor stream prevailing in winter, the southwest water vapor stream coming from the Bay of Bengal and the Arabian Sea in spring and summer, and the southerly water vapor stream entering from the western Pacific Ocean and the South China Sea. They are usually exported to Chinese mainland from west to east after the Yellow River joins the middle and lower reaches of the Yangtze River. The annual average total input of the three water vapor streams is 1909.4 mm, the annual total output is 1625.3 mm, and the annual net input is 284.1mm. The annual average water vapor content over Chinese mainland is 15. 1mm, which is slightly higher than that in Europe. The direction of water vapor transport over Chinese mainland has obvious seasonal variation.

Precipitation The average annual precipitation in Chinese mainland is 6188.9 billion cubic meters, and the precipitation depth is 648.4 mm, which is slightly higher than that in Asia (63 1 mm) and less than that in Europe (769 mm). Its basic characteristics are:

The general trend of (1) geographical distribution is decreasing from southeast to northwest. However, due to the influence of topography, there are also some high and low value precipitation areas with uneven distribution. The isoline of annual precipitation of 400 mm winds from Daxinganling in Northeast China to the border between China and Nepal, which is basically consistent with the isoline of annual average water vapor content of 10mm, and is also close to the boundary between the internal and external flow areas of Chinese mainland. The east of 400 mm annual precipitation isoline is semi-humid and humid area in China, and the west is semi-arid and arid area.

(2) The annual distribution of precipitation is very uneven. In most areas, the maximum continuous rainfall in four months accounts for more than 60% of the total annual rainfall, of which the northern and western Haihe River basins rent the Northeast Plain, Inner Mongolia Plateau, Tarim Basin, Qaidam Basin and most parts of Tibet, accounting for more than 80%.

(3) The annual precipitation process is closely related to the advance and retreat of the East Asian monsoon. In spring and summer, with the development and prevalence of the southwest and southeast monsoon, the rain belt moves from south to north, and the vast areas in the southwest and east have entered the rainy season one after another; In summer and autumn, with the attenuation and southward withdrawal of monsoon, the rain belt shrinks and weakens from north to south; The season with the least precipitation is from 10 to March of the following year. The precipitation in the northwest is closely related to the Atlantic water vapor flow, and the seasonal variation of precipitation is not as strong as that in the east.

Runoff The average annual runoff of Chinese mainland for many years is 2711500 million cubic meters, with an average annual runoff depth of 284 mm and a runoff coefficient of 0.44. Its basic characteristics are:

(1) The general trend of annual runoff geographical distribution is the same as that of precipitation, decreasing from southeast to northwest. The annual runoff depth isoline of 100 mm is roughly equivalent to the precipitation isoline of 400 mm, and the trend is consistent. Due to the influence of underlying surface, the geographical distribution of annual runoff depth is more complicated than that of annual precipitation.

(2) The annual distribution of river runoff is very uneven. Most rivers have obvious rainy and dry seasons, and the maximum runoff for four consecutive months accounts for more than 60% of the total annual runoff, including 60% ~ 70% in most areas south of the Yangtze River, east and southwest of Yunnan-Guizhou Plateau, 70% ~ 80% in most areas of Songliao Plain, North China Plain and Huaihe River Basin, and about 60% in the western region.

(3) Rivers in most areas are rain-fed, and the seasonal variation of runoff is closely related to the seasonal variation of precipitation, which also has obvious monsoon characteristics. Every year, with the arrival of the rainy season, the rain belt advances from south to north, and the river also enters the flood season from south to north. Generally, rivers in the south are from May to August, and rivers in the north are from June to September. Later, with the southward withdrawal of the rain belt and the end of the rainy season, the rivers entered the dry season from north to south in turn.

(4) The outflow area of Chinese mainland accounts for 65.2% of the total land area, and the runoff accounts for 96. 1% of the national runoff. The area of basically no runoff in the internal flow area is about 6.5438+0.6 million kilometers, accounting for 48% of the total area of the internal flow area. The annual net runoff of Chinese mainland is 2439 1 100 million cubic meters, of which1724.3 million cubic meters is directly injected into the ocean, and 7148 million cubic meters flows out through the land boundary.

Evaporation The annual evaporation in Chinese mainland is 364. 1 mm, and its regional distribution is closely related to the regional distribution of precipitation and runoff, and the general trend is decreasing from southeast to northwest. In the vast areas south of Huaihe River and east of Yunnan-Guizhou Plateau, the annual evaporation is 700-800 mm; The eastern part of Hainan Island and the southeast corner of Tibet can reach more than 1000 mm, which is the area with the largest evaporation in Chinese mainland. 400 ~ 600 mm in North China Plain; The northeast plain is only about 400 mm; The area to the west of Daxing 'anling, Inner Mongolia Plateau, Ordos Plateau, Alashan Plateau and northwest China is less than 300mm, which is the area with the smallest evaporation in Chinese mainland, and the Tarim Basin and Qaidam Basin are only 25mm. Due to the obvious seasonal changes in temperature and humidity conditions in Chinese mainland, the annual distribution of evaporation has also changed. The maximum evaporation for four consecutive months in a year accounts for about 50% ~ 60% of the total evaporation in the whole year. The variation range is slightly smaller than precipitation and runoff.

On the average for many years, the total annual water vapor input over Chinese mainland is 182 15.4 cubic kilometers, and the equivalent surface water depth is 1909.4 mm, of which about 3 1% is precipitation (586.2 mm) and 69% is transit water vapor, which is exported through Chinese mainland. The average annual evaporation in Chinese mainland is 364.3 mm, of which about 17% re-forms precipitation and returns to the ground (62.2 mm), and 83% is output with the airflow. The annual average precipitation in Chinese mainland is 648.4 mm, of which 90% is formed by water vapor outside China, and 10% is formed by evaporated water vapor in China. In the total annual water vapor output over Chinese mainland (1625.3 mm), the transit water vapor accounts for 8 1%, and the evaporation water vapor accounts for 19%. The sum of it and the overseas runoff of mainland rivers of 284. 1 mm is 1909.4 mm, which is equal to.

Comparing Chinese mainland with Europe and Oceania, it is not difficult to find that the annual net water vapor input, annual precipitation, annual evaporation and extrahydrological circulation coefficient (KI) and other water balance factors and water cycle parameters in Chinese mainland are similar to those in Europe. The contribution of hydrological internal circulation coefficient (KE) and hydrological internal circulation to precipitation is similar to that of Oceania. According to the preliminary analysis and research of scientists, this interesting phenomenon appears because the terrain of Chinese mainland is ladder-shaped with high west and low east and oblique east. Under the control of strong westerly circulation, East Asia has become a very favorable place for water vapor transportation and diffusion from west to east. A large amount of water vapor imported from the south and west boundaries is easily transported out of the boundary from the east boundary, and there is no chance to participate in the hydrological internal circulation. This income and expenditure situation of more water vapor input and more water vapor output is very similar to that of Oceania, which is an important reason for the inactivity of water internal circulation in Chinese mainland.

Water balance and water cycle at regional scale in China

China has a vast territory and complex terrain, spanning nine climatic zones from tropical zone to cold zone from south to north, and showing a changing trend from humid, semi-humid to semi-arid, arid and even extreme drought from southeast to northwest. The regional water cycle in different places is very strong, with obvious differences. Based on the study of regional scale water cycle and water balance in China, and considering the geographical distribution of major river basins, hydro-climatologists divide Chinese mainland into six regions, including South China, Yangtze River, Southwest China, North China, Northeast China and Northwest China, and calculate water balance and water cycle elements respectively.

South China South China mainly includes the Pearl River Basin and coastal rivers in Zhejiang and Fujian, with an area of 654.38+0.778 million square kilometers, belonging to a humid climate zone. South China is close to the South China Sea and the East China Sea, and the southerly airflow west of the Pacific subtropical high transports abundant water vapor over the area, making the water vapor content, annual net water vapor input, annual precipitation, annual runoff and annual evaporation above it rank first in the six areas. The annual total water vapor input over South China is 13036.2 mm, of which 13.9% forms precipitation PI, and 86. 1% is directly exported abroad. The annual total evaporation is 803.0 mm, of which 7.0% re-forms precipitation PE, and 93.0% is brought into the East China Sea by the westerly airflow at the southeast border. The annual total precipitation is 187 1.2 mm, of which about 97.0% is formed by imported water vapor, and only 3.0% is formed by evaporated water vapor in the region. About 57.0% of the total annual precipitation passes through the Pearl River and the southeast coastal rivers and is injected into the ocean in the form of surface runoff. The hydrological internal circulation process in South China is not very strong, KE is at the bottom of the six regions, while the hydrological external circulation coefficient KI ranks second, indicating that its precipitation mainly comes from external water vapor. The main reason why the hydrological internal circulation process in South China is inactive and the external circulation is very active is that it is located in the main output area of water vapor in the eastern part of China, and the land evaporation water vapor in the area is quickly carried out of the country by the strong westerly wind, so there is little chance to participate in the local water circulation process again. The abundant water vapor brought by southerly airflow is blocked by many mountains such as Daiyun Mountain and Wuyishan Mountain, which run from southwest to northeast in China, and forced to rise, resulting in cloudy and rainy weather and strong hydrological external circulation.

Yangtze River Basin The Yangtze River Basin mainly includes the Yangtze River Basin, with an area of 6.5438+0.778 million square kilometers, belonging to a humid climate zone. In spring and summer, the water vapor from the Bay of Bengal and the South China Sea meets the cold air from the north in the middle and lower reaches of the Yangtze River basin, forming abundant precipitation. Heavy rains often occur during plum rains and when typhoons land. In autumn and winter, with the transition from summer circulation to winter circulation and the establishment of winter circulation, the northerly airflow goes south, covering most areas of the Yangtze River. If you encounter a strong southerly airflow, it will also form more rain and snow. In the total annual water vapor input in the Yangtze River basin, precipitation PI accounts for 28.2%, and transit water vapor accounts for 765,438+0.8%. The annual evaporation of 14. 1% forms precipitation PE and returns to the ground, and 85.9% enters North China and East China Sea through the northern and eastern borders. 93.5% of the total annual precipitation is formed by imported water vapor, and only 6.5% is formed by evaporated water vapor in the region; 54.2% of the total annual precipitation enters the sea through the Yangtze River in the form of river runoff. The Yangtze River basin ranks first among the six regions in China, indicating that its hydrological internal circulation is very active. This is because the Yangtze River basin is vast, and low-value systems such as cyclone wave, southwest vortex and shear line are active, so the evaporated water vapor has more opportunities and better conditions to form precipitation again.

Southwest China covers an area of 846,5438+0,000 square kilometers, mainly including the cross-sectional landscape system and the Yarlung Zangbo River in Tibet, belonging to a humid climate zone. The southwest region is located on the southeast edge of the Qinghai-Tibet Plateau, and the Hengduan Mountain system in the west runs north-south, which is conducive to the water vapor flow upstream along the valley and directly to the Yarlung Zangbo River valley. The southeast of this area is only about 200 meters above sea level, and the water vapor flow from the Bay of Bengal enters from the south and west borders of this area, departs northeast through Kunming, Guiyang and Zhijiang, and enters the Yangtze River area from the north border. The important characteristics of southwest China are obvious vertical zoning of hydrology and climate, precipitation and runoff increase with altitude, temperature decreases with altitude, and evaporation decreases with altitude. The vertical zoning of water balance factor reflects the vertical characteristics of water cycle in this region, that is, the precipitation runoff in high altitude areas flows into the ocean through rivers, and the evaporated water vapor in low altitude areas climbs along the river valley to form precipitation at high altitude. 20.4% of the total water vapor input in southwest China forms precipitation PI, and 79.6% is exported overseas. 10. 1% annual evaporation forms precipitation PE, and 89.9% of it is exported abroad; In the annual precipitation, 95.7% is formed by imported water vapor, and 4.3% is contributed by evaporated water vapor in the region. 57.3% of the annual precipitation becomes river runoff, which flows out of the country through Nujiang River, Lancang River and Yuanjiang River. The hydrological internal and external circulation coefficients KE and KI are in the forefront, and it takes only 4.7 days for the water vapor above them to be completely updated, indicating that the hydrological internal and external circulation in this area is very active.

North China North China covers an area of 6.5438+0.43 million square kilometers, mainly including the middle and lower reaches of the Yellow River, the Hailuan River and the Huaihe River Basin, and belongs to a sub-humid and sub-arid climate zone. Controlled by Mongolian high pressure, the northwest airflow of polar and metamorphic polar continental air masses prevails in North China in winter, which is cold and dry. Cyclone activity is frequent in spring, with more precipitation than in winter, but it is dry and windy in early summer. In summer, under the influence of continental depression and Pacific subtropical high, tropical marine air masses arrive in this area with abundant water vapor, which is the season with the most precipitation in a year, with continuous heavy rains and rivers entering the flood season; The arrival of polar continental air mass in autumn will soon rebuild the circulation situation in winter. The maximum continuous precipitation in four months in North China can account for more than 80% of the annual precipitation, and the Cv values of precipitation and runoff are as high as 0.3 and 0.8 respectively. The annual and inter-annual changes of water balance elements are very violent, which is an important feature of the hydrological climate in this area. The water vapor over North China is mainly imported from its southern border, with an average annual total water vapor input of 2550 mm, of which 19.6% forms precipitation PI, and 80.4% is transit water vapor. The annual evaporation is 433.5 mm, of which 9.8% forms precipitation PE and returns to the ground, and 90.2% is transported abroad with the airflow; The annual precipitation is 543.5 mm, of which 92.2% is formed by water vapor imported from abroad, and the precipitation formed by evaporation in the region only accounts for 7.8%; 20.2% of the annual precipitation forms runoff, which is injected into the Bohai Sea from Haihe River, Luanhe River and other water systems to complete the annual water cycle and water balance. The coefficient of internal circulation in North China is large, and the contribution of hydrological internal circulation to precipitation is second only to that in Northeast China and greater than that in other regions, indicating that internal circulation is more active. However, the external circulation coefficient KI is only slightly higher than that in the northwest, and the external circulation is not active.

Northeast China covers an area of 6.5438+0.246 million square kilometers, which is the region with the highest average latitude in China, mainly including Songhua River and Liaohe River Basin, and belongs to a sub-humid climate zone except the area west of Daxing 'anling. Northeast China is surrounded by Daxing 'anling, Xiaoxing 'anling and Changbai Mountain in the west, north and east, and the central plain is open to the south, which is a pocket terrain surrounded by mountains on three sides and facing the Bohai Sea. Winter is controlled by the northwest airflow, with sunny and dry weather and less precipitation. In summer, the southeast monsoon carries rich water vapor into the bag-like terrain, with more precipitation, and the precipitation on the windward slope in mountainous areas can reach 1000 ~ 1200mm. The water vapor over the northeast is mainly imported from its western and southern borders, with the western border accounting for 70% and the southern border accounting for 30%. The total water vapor input in the whole year is 2252.9 mm, of which precipitation accounts for 22.5% and transit water vapor accounts for 77.5%. The annual total evaporation is 43 1.6mm, of which 1 1.3% forms precipitation in the area and returns to the ground, and 88.7% is exported with the airflow. Of the total annual precipitation of 556.2 mm, 9 1.2% is formed by imported water vapor and 8.8% is formed by evaporated water vapor in this area. 24.5% of the precipitation forms runoff, which mainly flows into the Sea of Okhotsk through Songhua River and Heilongjiang, and flows into the Bohai Sea through Liaohe River. The hydrological internal circulation coefficient KE in Northeast China is only smaller than that of the Yangtze River, ranking second, indicating that its hydrological internal circulation is more active and contributes greatly to precipitation. However, the coefficient of hydrological external circulation KI is small, only slightly larger than that in North China and Northwest China, indicating that the hydrological external circulation in this area is not active.

Northwest China covers an area of 3.437 million square kilometers and is located in the hinterland of Eurasia, mainly including inland rivers in the northwest, with a typical continental climate. Except for the semi-arid area in northern Xinjiang, it belongs to arid and extremely arid areas. Westerly jet prevails all the year round in the northwest, controlled by Mongolian high pressure in winter, and the climate is dry and cold; Summer is mainly controlled by heat and low pressure, with occasional convective precipitation; Spring and autumn is a transitional season, and the high and low pressure systems have their ups and downs, and the weather is changeable. Northwest China has a vast territory and different water vapor sources. In northern Xinjiang, the water vapor from the Atlantic Ocean and the Arctic Ocean is mainly carried by the westerly circulation. South Xinjiang is mainly from the west and southwest airflow of subtropical jet, which carries the water vapor of Arabian Sea through Central Asia and across Pamirs. The water vapor in the Bay of Bengal is mainly carried by the southwest monsoon in the eastern region and enters along the Hengduan Mountains and the eastern Qinghai-Tibet Plateau. The annual total water vapor input in northwest China is10610.9mm, of which only 14.4% forms precipitation PI, and the remaining 85.6% is transit water passing through this area. The annual total evaporation is 133.6 mm, of which only 7.2% re-forms precipitation PE, and the remaining 92.8% is exported overseas with the airflow; Annual total precipitation 164.6 mm, of which 92.8% is formed by imported water vapor and 7.2% is formed by local evaporated water vapor. About 0. 1% of the total precipitation passes through Irtysh River and Yili River, and the remaining 99.9% is consumed by evaporation. The hydrological internal and external circulation coefficients KI and KE in northwest China are the lowest in China, the annual input and output of water vapor are almost equal, and the net input is very small, so the outflow is very small, indicating that the hydrological internal and external circulation is not active.