Xihai

Qinghai Lake

synonym

Xihai (another name for Qinghai Lake) generally refers to Qinghai Lake (Qinghai Lake in Qinghai Province)

This entry is compiled and applied by "popular science China" Science Encyclopedia

to examine

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Qinghai Lake is called "cuowenbu" (meaning "blue sea") in Tibetan. Located in the northeast of Qinghai Tibet Plateau and Qinghai Province, it is the largest inland lake in China. It is formed by the fault collapse between Datong mountain, Riyue mountain and Nanshan Mountain in Qinghai Province.

On July 30, 2012, the latest remote sensing monitoring results of Qinghai Meteorological Science Research Institute showed that the area of Qinghai Lake continued to increase for 8 years.

At 9:50 on October 20, 2014, a spectacular scene of "dragon absorbing water" appeared on the north side of Haixin mountain in Qinghai Lake.

Formation and evolution

Cause of formation

The margin of the lake basin is connected with the surrounding mountains by faults. In the early stage of its formation 200-200 million years ago, it was a large freshwater lake connected with the Yellow River system. At that time, the climate was mild and rainy, and the lake water flowed into the Yellow River through the inverted River in the southeast, which was an outflow lake. Up to 130000 years ago, due to the neotectonic movement, the surrounding mountains were strongly uplifted. From the end of Pliocene, the Riyue mountain and yeniushan mountain in the east of the lake rose and uplifted rapidly, which blocked the inverted river flowing into the Yellow River and forced it to flow into Qinghai Lake from east to West. Gahai Lake and Erhai Lake appeared, and then separated into Yanhu lake, Shadao lake and other sub lakes.

Change of circumstances

Due to the blockage of the spillway, Qinghai Lake has evolved into a closed lake. In addition, the climate has become dry, and Qinghai Lake has gradually changed from fresh water lake to salt water lake. In the Northern Wei Dynasty, the perimeter of Qinghai Lake was called Qianli, 400 kilometers in the Tang Dynasty, and 350 kilometers in the Qing Dynasty. In the front of Buha River Delta, there are ancient lake dyke sites about 20 km away; chahancheng (built in Han Dynasty) 25 km away from the East Bank of the lake was originally on the lakeside. The East and west sides have retreated 25 km and 20 km respectively, and the water level has dropped by about 100 meters. Qinghai Lake is an oval shape with a circumference of more than 300 kilometers.

In 1908, Russian Kozlov speculated that the water level of the lake at that time was 3205 meters, and the lake area was 4800 square kilometers; the surveying and mapping data in the 1950s showed that the water area of Qinghai Lake was more than 4568 square kilometers; the topographic map published in the 1970s showed that the water level of the lake was about 3195 meters. The lake covers an area of 4473 square kilometers. In 1988, the water level was 3193.59 meters, and the lake area was 4282 square kilometers. In 2000, through the analysis of remote sensing satellite data, the area of Qinghai Lake was more than 4256.04 square kilometers. In August 2013, the area of Qinghai Lake was 4337.48 square kilometers.

The lake has a volume of 73.9 billion cubic meters, the longest is about 104 kilometers, the widest is about 62 kilometers, the maximum water depth is 31.4 meters, the average salinity of the lake is 12.32 g / L, and the salt content is 1.25%.

In August 2017, the area of Qinghai Lake was 4435.69 square kilometers, an increase of 60.19 square kilometers compared with the same period of last year, and an average increase of 101.54 square kilometers compared with the same period of previous years (2005-2016)

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Basin characteristics

geographical environment

Qinghai Lake is 105 km long, 63 km wide, and 3196 m above sea level. It is the largest inland lake in China. It is located in the northeast of Qinghai Tibet Plateau and the northwest of Xining City, between 99 ° 36 ′ - 100 ° 16 ′ E and 36 ° 32 ′ - 37 ° 15 ′ n. The lake is surrounded by four towering mountains: Datong mountain in the north, Riyue mountain in the East, Nanshan Mountain in Qinghai in the South and rubber mountain in the West. The altitude of these four mountains ranges from 3600 to 5000 meters. Qinghai Lake covers an area of 4456 square kilometers, with a circumference of more than 360 kilometers, more than twice the size of the famous Taihu Lake. The lake is long from east to west, narrow from north to South and slightly oval. The average water depth of Qinghai Lake is more than 21 meters, the maximum water depth is 32.8 meters, the storage capacity is 105 billion cubic meters, and the elevation of the lake is 3260 meters. It's about 200 kilometers from Xining. There are nearly 30 rivers in the lake area. On the East Bank of the lake, there are two sub lakes, one is Gahai, with an area of 48 square kilometers, which is saline water; the other is Erhai, with an area of 8 square kilometers, which is fresh water.

Climatic characteristics

Qinghai Lake has a plateau continental climate with sufficient light and strong sunshine; it is cold in winter and cool in summer, short in warm season, long in cold season, strong wind and sandstorm in spring; it has less rainfall, hot and rainy seasons, and distinct dry and wet seasons.

illumination

Most of the sunshine hours in the lake area are more than 3000 hours, which is 700 hours higher than that in the same latitude area in the east of Qinghai, and the annual sunshine percentage is 68-69%. The annual total radiation is 171.461-106.693 kcal / cm2 · a, which is 10-40 kcal / cm2 · a higher than that of North China Plain and loess plateau at the same latitude.

air temperature

The temperature in the East and south of the lake area is slightly higher, with the annual average temperature between 1.1 ℃ and 0.3 ℃; the temperature in the West and north is slightly lower, with the annual average temperature between - 0.8 ℃ and 0.6 ℃, the average maximum temperature between 6.7 ℃ and 8.7 ℃, the average minimum temperature between - 6.7 ℃ and 4.9 ℃, the extreme maximum temperature between 25 ℃ and 24.4 ℃, and the extreme minimum temperature between - 31 ℃ and - 33.4 ℃.

water content

The annual precipitation in the lake area is less. However, the annual precipitation in the East and south is 412.8 mm, that in the south is 359.4 mm, that in the northwest is 370.3 mm, that in the west is 360.4 mm and 324.5 mm. The annual evaporation is 1502 mm, which far exceeds the precipitation. The seasonal variation of precipitation in the lake area is large. The precipitation is mainly concentrated from May to September, and the rain is hot in the same season.

Gales and sandstorms

The days of gale and sandstorm in the lake area are one of the most frequent areas in the province. From February to April every year, strong wind often occurs from afternoon to evening, and northwest wind prevails. Take Gangcha as an example. Gales (≥ 17 m / s) average 47.3 days per year, most in February to April, with an average of 5.9 to 9.3 days, and most in March, with 19 days. The annual average duration of sandstorm is 14 days. Buha River mouth Bird Island, a key protected area, is windy in the northwest, with the maximum wind force of 9-10. Due to the high altitude of the lake area, there are many westerlies in the lake area, and the high air has a great impact on the lake area. The wind speed is the highest in winter and spring, and smaller in summer and autumn. Under the action of wind, the general wave is 2-3, the maximum wave is 7-8, and the number of days with wave above 6 is about 40 days.

water temperature

The water temperature of Qinghai Lake changes with seasons. In summer, the lake water temperature has obvious positive temperature layer phenomenon, the highest is 22.3 ℃ in August, with an average of 16 ℃; the lower layer temperature is relatively low, with an average of 9.5 ℃ and a minimum of 6 ℃. In winter, the lake surface freezes, and the temperature of the lake appears inversion layer. In January, the temperature of the upper layer is - 0.9 ℃, and the temperature of the bottom layer is 3.3 ℃. After thawing in spring, the surface water temperature of the lake began to rise again, and gradually returned to the temperature in summer and season.

Ice situation

The freezing temperature of Qinghai lake water is slightly lower than 0 ℃ because it contains a small amount of inorganic salts. From the middle of November every year, the temperature in the lake area drops to below 0 ℃, and the temperature is the lowest in January of the next year. The whole lake forms a stable ice sheet. The annual average ice closure period is 108-116 days, the shortest is 76 days, and the longest is 138 days. The ice thickness is generally 40 cm, and the maximum ice thickness is 90 cm. After ice sealing, the ice surface is flat, and cracks and gullies often appear due to strong wind. In winter, you can enjoy the scenery of lakes and mountains. It's all white and silver. In the middle of March, the ice sheet broke and ice floes appeared on the lake. Under the action of wind, huge icebergs were formed and floated to the shore. The largest iceberg volume was about 10 cubic meters. After the middle of April, the ice in the lake completely melted.

Lake water system

The water supply source of Qinghai Lake is river water, followed by spring water and precipitation at the bottom of the lake. There are more than 70 rivers around the lake, showing obvious asymmetric distribution. There are many rivers in Hubei, northwest and southwest bank, with large drainage area and many tributaries; there are few rivers in Southeast and south bank, with small drainage area. Buha River is the largest river flowing into the lake. It originates from amuniniku mountain, a branch of Qilian Mountain. It is about 300 km long and 92 km long. There are dozens of tributaries and more than 10 larger tributaries. The downstream river is about 50-100 m wide and 1-3 m deep, with pH 8-8.2. The basin covers an area of 16570 square kilometers, accounting for about 1 / 2 of each river basin in the lake area. The annual runoff is 1.12 billion cubic meters, accounting for 60% of the runoff into the lake.

There are more than 40 rivers in Qinghai Lake, mainly Buha River, Shaliu River, wuhaalan River and khargai River, which are recharged by runoff every year. The annual runoff of these four rivers reaches 1.612 billion cubic meters, accounting for 86% of the runoff into the lake. It is an area where fish return to spawn and birds are concentrated. Qinghai Lake supplies 1.335 billion cubic meters of water from rivers, 1.557 billion cubic meters of precipitation and 401 million cubic meters of groundwater every year, with a total supply of 3.493 billion cubic meters. The lake area is windy and evaporates rapidly, with an annual evaporation of 3.93 billion cubic meters

Chinese PinYin : Xi Hai