Hydrological characteristics of the upper, middle and lower reaches of the Yangtze River

1, water quantity

The Yangtze River is the most abundant river in China, with a total water resource of 961600 million cubic meters, accounting for about 36% of the total river runoff in China and 20 times that of the Yellow River. The Amazon River and the Congo River (Zaire River) are second only to the equatorial rainforest, ranking third in the world.

The parana river-La Plata River in South America and the Mississippi River in North America, which are similar in latitude to the Yangtze River basin, have a basin area larger than that of the Yangtze River, but their water consumption is far less than that of the Yangtze River. The former accounts for about 70% of the Yangtze River, while the latter accounts for about 60% of the Yangtze River. ?

The total water resources in the Yangtze River basin is 96 16 billion cubic meters, including 95 13 billion cubic meters of surface water, 246.3 billion cubic meters of groundwater and 236 billion cubic meters of reused water. Due to the large population in the basin, the per capita water consumption is 2760m3, which is only 1/4 of the world's per capita water consumption. The characteristics of water resources in the Yangtze River are mainly reflected in the temporal and spatial distribution of river runoff, and the surface water resources in the basin account for 99% of the total water resources.

In surface water resources, river runoff accounts for more than 96%. River runoff in flood season generally accounts for 70% ~ 75% of the annual runoff. The regional distribution of runoff is also very uneven. The water yield per unit area is the least in Jinsha River and Hanjiang River, and the largest in Poyang Lake and Dongting Lake. According to administrative regions, Qinghai and Henan are the smallest, and Hunan is the largest. ?

2. Drought and flood disasters

The historical records of droughts and floods in various areas of the Yangtze River Basin have a long history. The earliest drought was recorded in the fifth year of Emperor Hui of the Han Dynasty (BC 190), and "Summer was a great drought, rivers were scarce, and the valley was extinct" (Records of Five Elements of Han Dynasty). In the third year of Gao Hou (BC 185), "In summer, rivers and rivers flooded with Han water, and there were more than 4,000 refugees" ("Han Gao Hou Ji").

Typical dry years in historical periods with detailed records and good comparability are 167 1, 1679, 1778 and 1835. Typical flood years are 1586, 1663, 1788, 183 1, 1853, 1867 and1.

The above-mentioned typical drought and flood years are mostly concentrated in the Qing Dynasty, which is mainly because the Qing Dynasty is the closest and the historical documents are well preserved and described in detail, which does not mean that the drought and flood disasters in the Qing Dynasty are the most frequent. Some serious events in drought and flood years before the Qing Dynasty were either described briefly or incompletely in the literature, and most of them were never selected.

In the past hundred years, there have also been typical years of severe drought and flood disasters in the Yangtze River basin, and there are a lot of measured data and analytical research documents for reference, so I won't repeat them here. The selected 1 1 typical drought and flood years are divided into three grades according to the disaster severity recorded in historical documents, namely, drought, severe drought, severe drought and flood, severe flood and severe flood.

The geographical distribution of drought and flood disasters in the Yangtze River basin is very strong, and the drought and flood disasters in different regions vary greatly. According to the data of central weather bureau (now called "Atlas of Drought and Flood Distribution in China in Recent 500 Years" edited by Institute of Meteorological Science of China Meteorological Bureau), the series of drought and flood shows five grades: grade I-waterlogging, grade II-partial waterlogging, grade III-normal, grade IV-partial drought and grade V.

There are 37 stations in the east of the Yangtze River Basin 100E, and the frequency distribution map of historical drought (V-level) and flood (I-level) in the Yangtze River Basin is obtained through sorting and analysis. The average frequency of severe drought in the flow field is 5.55%, and the probability of drought in the middle and lower reaches is higher than that in the upper reaches. The drought frequency in the Yangtze River Delta, the middle and lower reaches of the main stream and Dongting Lake is as high as 9.0%, which is the highest in the whole flow field.

Followed by the upper reaches of Jialing River, the highest drought frequency in the middle is above 7.0%. The average frequency of flood disasters in the basin is 7.97%, which is obviously higher than that of drought. The regional distribution of flood disasters is basically consistent with drought, that is, the middle and lower reaches are generally higher than the upper reaches.

There is an east-west high-frequency flood disaster zone in the main stream and the middle and lower reaches of the two lakes, in which the northern part of Poyang Lake and the middle reaches of Yuanjiang River and Lijiang River to Dongting Lake are two high-frequency central areas of flood disaster, and the central frequency is as high as 12.0%.

Jialing River and Hanjiang River in the upper reaches of the Yangtze River are the third largest high-frequency flood areas. The above-mentioned flood high-frequency zones and centers are basically consistent with the Meiyu zone in the middle and lower reaches of early summer, the concentrated rain zone in the upper reaches of midsummer and the main rainstorm centers in the basin.

The historical droughts and floods in the Yangtze River are also unevenly distributed in time. According to the data of 1000 years published in Climate, the fifth issue of China Blue Book of Science and Technology, through supplementary analysis, the historical dry and wet climate and periodic changes of drought and flood in the Yangtze River basin are obtained. The table is as follows.

In recent 1000 years, the Yangtze River basin has experienced three large dry and wet climate cycles, the shortest wet season and dry season is 120 years, and the longest is 220 years, including 3-5 small drought and flood periods respectively. Since 1980s, the Yangtze River has entered a new humid climate period, and it is currently in the first small flood period of this new humid period. The figures in brackets in the table are the reference values of the forecast.

Extended data

Climatic characteristics

The Yangtze River basin has a warm climate and abundant rainfall. Because of its vast territory and great terrain changes, the climate types are diverse. Natural disasters such as floods, floods, droughts and hail occur from time to time. There are four distinct seasons in the middle and lower reaches of the Yangtze River, and Leng Xia is hot in winter. The annual average temperature is 16 ~ 18℃, the highest temperature in summer is about 40℃, and the lowest temperature in winter is about MINUS 4℃.

The climate in Sichuan Basin is mild, and the temperature in winter is about 5℃ higher than that in the middle and lower reaches. There are four seasons like spring in Kunming. It has a typical three-dimensional climate of Jinsha River Canyon, with snow on the top and spring at the foot of the mountain. Jiangyuan region belongs to a typical alpine climate, with an annual average temperature of -4.4℃, four distinct seasons, dry winter, low pressure, long sunshine, much hail and strong wind.

The southeast monsoon and southwest monsoon, which come from the Pacific Ocean and the Indian Ocean respectively and carry a lot of water vapor, prevail in the Yangtze River basin in summer and around summer, and precipitation is formed in the process of monsoon advance and retreat and cold and warm airflow confrontation. In mid-June, the ridge line of the subtropical high jumped to 20 ~ 25 north latitude, and the middle and lower reaches entered the rainy season. In mid-July, it jumped to the north, plum blossoms appeared in this area, and it entered the summer drought weather.

In winter and around winter, dry and cold air from polar regions and high latitudes in Asia prevails in the basin, with little precipitation. The average annual precipitation in the Yangtze River basin is nearly 1 100 mm ... April to 10 is the rainy season, and its precipitation can account for 85% of the annual precipitation. Except for White in Jinsha River and Luhuo in Yalong River, there are heavy rains in the remaining 6,543.8+0.5 million km.

There are mainly two areas with high rainstorm value in the basin: one is centered in northeast Jiangxi, including northern Hunan, southern Anhui and southern Hubei, with annual average precipitation1800 ~ 2000 mm; Second, the Ya 'an area in western Sichuan, including eastern Sichuan, northern Sichuan, southwestern Shaanxi, western Hubei and northwestern Yunnan, has an average annual precipitation of about 2,000 mm ... The daily rainstorm coverage in the basin is about 40,000 ~10.5 million km, with a maximum of 210.3 million km.

The precipitation of each tributary is: 600 ~ 800 mm in the upper reaches of Yalong River and 900 ~1800 mm in the middle and lower reaches; 370 ~ 600 mm in the upper reaches of Dadu River and 652 ~ 1949 mm in the middle and lower reaches; The upper reaches of Tuojiang River 1200 ~ 1400 mm, Longmen Mountain is a rainstorm area, and the middle and lower reaches are 900 ~1000 mm; Jialing River Basin 1494mm, and the southern foot of Daba Mountain is a rainstorm area.

Wujiang river basin1163mm; Qingjiang river basin 1400mm, Enshi and Wufeng are the rainstorm centers in western Hubei; Hanjiang river basin 700 ~ 1 100 mm; Zishui Valley 1200 ~ 1800 mm, Liuduzhai, Zhexi and Taojiang areas are rainstorm areas. Yuanjiang river basin 1 100 ~ 1800 mm; Lishui river basin 1300 ~ 1800 mm, Wufeng and Hefeng are rainstorm areas; Ganjiang river basin 1400 ~ 1800 mm.

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