Yiyang Luoyang weather

The Yellow River is the second longest river in China, second only to the Yangtze River, with a total length of 5,464 kilometers. It zigzagged through Qinghai, Sichuan, Gansu, Ningxia, Suiyuan, Shaanxi, Shanxi, Henan and Shandong provinces, and flowed eastward into the Bohai Sea, where more than 30 major tributaries and countless streams gathered along the way, with a drainage area of more than 750,000 square kilometers. The middle reaches flow through the vast loess plateau, and many tributaries carry a lot of sediment into it, which is the river with the largest sediment concentration in the world. This river is yellow, hence its name.

The Yellow River originates from the Zhanzonglie Canal at the northern foot of Bayan Kara, Qinghai, with an altitude of more than 5,400 meters, and the surrounding mountains are covered with snow all year round. There is a sea of stars at the source of the Yellow River, which is a swamp of countless small lakes. After leaving Xinghai, enter Eling Lake and Zhaling Lake to Maduo, bypass Jishishan and Xiqingshan, and cross Longyangxia to Guide, Qinghai, with a total length of 1900 kilometers. The upstream section is from Guide to Hekou Town, Suiyuan Province, with a total length of 1500 kilometers. The Yellow River is in Gansu, passing through many grand canyons and gathering many tributaries. The middle reaches from Hekou Town to Yujin, with a total length of 1 100 kilometers. The river flows south through the Loess Plateau, carrying a lot of sediment, rushing down to Hukou, where the terrain is steep, forming Hukou Waterfall, and then passing through Longmen Gorge to Tongguan, the river channel becomes wider, and the water volume increases greatly because of the confluence of Qin Fen, Luohe and Xiaoshui tributaries. When the river reaches Tongguan, it is blocked by Huashan Mountain, turns east, crosses Sanmenxia to Luo Yu, and then enters the plain area. The downstream section flows into the Bohai Sea from Jinmeng to Lijin County, Shandong Province, with a total length of more than 870 kilometers. Due to sediment deposition and slow water flow, dikes are built on both banks and become rivers above the ground.

The headwaters and upper reaches of the Yellow River are the most tortuous, followed by the middle reaches, and the lower reaches are straight. From Lanzhou to Tongguan, the river bypasses a rectangle on three sides, which is the famous Hetao, about 2000 kilometers long. Ancient rivers drifted downstream, sometimes the river flowed into the Bohai Sea in the northern part of Shandong hills, and sometimes it seized the Huaihe River and flowed into the Yellow Sea in the southern part of Shandong hills, with a distance of 500 kilometers.

Historically, the Yellow River has flooded cities. According to records, over the past 2000 years, the lower reaches of the Yellow River have burst its banks 1500 times and changed its course on a large scale for 26 times. The flood-stricken area reaches Tianjin in the north and Jiangsu and Anhui in the south, reaching 250,000 square kilometers. The total amount of sediment carried by river water exceeds1600 million metric tons every year on average. Due to the low terrain, gentle river slope and slow flow rate, a large amount of sediment is deposited on the river bed, with an average of more than 400 million metric tons per year. The rest of the sediment flows to the estuary and alluvial into the estuary delta extending to the sea, with an average of more than 20 square kilometers of land reclamation every year. The Yellow River basin has fertile soil, rich products and magnificent mountains and rivers. Residents account for almost a quarter of the total population of China, while cultivated land accounts for about 40% of the country.

The Yellow River basin is bounded by latitude 32-42 N and longitude 96- 1 19 E, with a difference of latitude 10 between north and south and longitude 23 between east and west. The basin covers an area of more than 752,000 square kilometers, with a total length of 5,464 kilometers and a drop of 4,830 meters from the source to the estuary. Rocky mountain area accounts for 29%, loess hilly area accounts for 46%, sandstorm area accounts for 1 1%, and plain area accounts for 14%. The natural landscape varies greatly from place to place, especially the largest loess plateau in the world, where soil erosion is very serious.

The Yellow River basin belongs to continental climate. Most areas above Lanzhou are semi-humid areas, while those below Lanzhou are arid areas in northwest, humid areas in south and southeast, and the rest are semi-arid and semi-humid areas. Winter is controlled by Mongolian high pressure, prevailing northerly wind, low temperature and little precipitation; In spring, the Mongolian high weakened, and the western Pacific subtropical high began to extend northward and westward, with the temperature rising and precipitation increasing. In summer, most areas are affected by the western Pacific subtropical high, with southerly winds and abundant water vapor, which is the most rainy period in a year; In autumn, the western Pacific subtropical high gradually weakened, the Mongolian high spread southward, and the precipitation began to decrease, but continuous rainy weather often appeared. The regional distribution of temperature is characterized by a gradual decrease from south to north and from east to west. The annual average temperature is higher than 14℃ in the highest area and lower than -4℃ in the lowest area. The annual extreme maximum temperature in Luoyang basin is 44.2℃, and the annual extreme minimum temperature in Heyuan area is -53.0℃. The precipitation gradually decreases from southeast to northwest. The area with the largest annual average precipitation for many years is Qinling Mountain, which locally exceeds 900 mm, and the station with the largest annual precipitation is Taishan Peak, reaching 1 108.3 mm; The areas with less annual precipitation are Hangjinhou Banner and He Lin, Inner Mongolia, which are below 150 mm, and the station with the least annual precipitation is Shanba, Hangjinhou Banner, Inner Mongolia, which is only138.4 mm. The rainfall intensity in the upper reaches is small, the duration is long, there are few heavy rains, and the daily precipitation rarely exceeds 50 mm; The rainfall intensity in the middle and lower reaches is high, the duration is short, and there are more heavy rains. There was a rainstorm in Wushenqi, the border of Shaanxi and Inner Mongolia, 1 August, 9771day, and the center of the rainstorm was full of trees. The rainfall during 1400 hours is 1400 mm (survey value), which exceeds the world record. Between Sanmenxia and Huayuankou, 1982, there was a rainstorm from the end of July to the beginning of August. The 24-hour rainfall in Shizhen Town, Yiyang County is 734.3 mm, which is also a rare rainstorm in the Yellow River Basin.

Due to the influence of climate, topography, landforms and other natural geographical landscapes, the hydrological situation of the Yellow River is very complicated, which mainly has the following three characteristics:

First of all, runoff changes greatly in time and space. The ratio of wet year to dry year in the main stream is 2.5~3.5 times, and that in the tributaries is 2.5~40.8 times. The coefficient of variation of annual runoff in each region is 0. 1 ~ 0.53. The difference of runoff depth between multi-water area and low-water area is more than 140 times. The maximum annual runoff coefficient is 0.7 and the minimum is only 0.0 1.

Second, the flood season is long and there are many floods. There are four flood seasons in a year: rainy season, autumn flood season, autumn flood season and peach flood season, with a total duration of 10 month. The flood season in summer and autumn is called flood season and is formed by rainfall. Its flood sources are above Lanzhou, between Shanxi and Shaanxi, between Longmen and Sanmenxia, between Sanmenxia and Huayuankou, and Dawenhe River Basin. The upstream flood fluctuates slowly and lasts for a long time. The average flood duration at Lanzhou Hydrological Station is 40 days, with the longest 66 days and the shortest 22 days. The flood in the middle reaches fluctuates rapidly, especially in Shanxi and Shaanxi, and its duration is short. The average flood at Longmen Station in the main stream lasted 46 hours, with the longest 80 hours and the shortest 20 hours. The continuous flood usually lasts for 3-6 days, with an average flood of 8 hours, with a maximum of 30 hours and a minimum of 2 hours. Tributary floods are more violent; The flood in the lower mainstream mainly comes from the middle reaches, and its characteristics are related to the source, but it is also influenced by the buildings in the high sediment-laden river bed and beach area, which often causes abnormal changes in the flood evolution law. Ice flood mainly occurs in Ningxia, Inner Mongolia and the lower reaches of the Yellow River, all of which are formed by ice plugs and ice dams. The ice conditions in the lower reaches of the Yellow River are extremely unstable. About one-tenth of the years are not closed, and some years are closed three times. Since the 1960s, the ice situation has changed greatly and the ice disaster has been alleviated due to the ice prevention operation of Sanmenxia and Liujiaxia reservoirs. The reach from Yanguoxia Reservoir to Liujiaxia reaches meandering at 196 1~ 1962, and the upstream of Qingtongxia Reservoir reaches meandering at 1967~ 1968. Taohong is a glacier flood formed by the melting and storage of ice water in the river channel when Ningxia and Inner Mongolia reach the river channel. Peach blossom season flows downstream, with low flood peak and slow fluctuation. After 1972, it is downstream irrigation, Sanmenxia Reservoir stores peach flood, and there is no peach flood peak downstream.