A rare autumn flood occurs in the Yellow River Basin this year! Why is it so "extreme"?

2021-10-14: [Article Link]. Since the beginning of this year, China's weather and climate are complex, and extreme weather and climate events have occurred frequently. It is hard to imagine that the Yellow River Basin after the fall has been rare for many years. The reporter contacted the Yellow River Basin Meteorological Center and the National Climate Center to answer you one by one. On September 27th, the flow of Tongguan Hydrological Station in the middle reaches of the Yellow River rose to 5020 cubic meters per second. In the middle and lower reaches, the water level is high due to the same amount of rainfall in the early period. From Sep 27th to October 5 the middle and lower reaches of the Yellow River is up to 9 days on time-3 number flood. In the lower reaches of the Yellow River, the most serious autumn flood occurred in 36 years in the Jinan section of the Yellow River! Late August this year since the Western North Pacific subtropical high abnormal strong north-Southwest warm air and southeast warm air along the subtropical high in the North. At the same time the westerly cold air activity frequently visit the middle reaches of the Yellow River. The same "energetic" cold and warm air continues to meet violently in the middle reaches of the Yellow River, forming a special and extremely rare autumn rain this year. The researchers found that the probability of autumn floods in the Yellow River is related to the autumn rain in West China. Among them, 2003 is the most typical. Affected by the autumn rain in West China, more than 10 floods occurred in the main and tributaries of the middle reaches of the Yellow River from the end of August to the beginning of October of that year, and the Yellow River beach areas in Shandong and Henan were seriously affected. In addition, in 1949 and 1964, autumn floods occurred in the Yellow River Basin due to the autumn rain in West China. Autumn rain in West China is a special seasonal rainy weather phenomenon in Sichuan, Chongqing, Weishui River Basin, Hanshui River Basin, Eastern Yunnan, Guizhou and other places, which can be continued from September to November. This year, the autumn rain in China began on August 23, 17 days earlier than usual, and the rainfall was also high. Compared with the autumn flood in 2003, the rainfall area and cumulative rainfall in the Yellow River Basin this year are similar, but the precipitation period is more concentrated and the accumulated rainfall is greater. If the time is extended to the entire main flood season, since June, 7 major weather processes have occurred in the entire Yellow River Basin, all affecting the middle reaches, 5 times affecting the downstream areas, and 2 times affecting the upstream areas. Especially Sep mid to, the middle and lower reaches of the Yellow River river basin there were 3 times strong precipitation process, respectively in September 17-19 and September 22-27 and October 2-6. The areas of the three precipitation processes are highly overlapping, mainly concentrated in the middle reaches of the Yellow River, such as the Shanxi-Shaanxi section and Henan, resulting in serious water from the middle reaches of the Yellow River and tributaries such as the main stream of the Yellow River and the tributaries of the Weihe River. Not only is qiu xun! Although the number flood is "late", in fact, the Yellow River Basin is not calm as a whole this year. First, the overall precipitation is too large and the spatial distribution is uneven. Since 2021, the average precipitation in the Yellow River Basin is 609.2mm, 42.9% more than the same period of the year, and 23.3% more than the same period last year, which is the most value since 1965. Compared with the same period of the year, except for the upstream east and the northern part of the Basin precipitation is less, the precipitation in the rest of the region is more than 8 to 2.7 times. Second, the middle and lower reaches of the flood season are concentrated and the local extremes are prominent. The average precipitation in the Yellow River Basin since the flood season (June 1) is 490.7mm, 48.7% more than the normal period, which is the maximum since 1961. The precipitation in the southeast and downstream of the middle reaches is more than 500mm, and in some areas it exceeds 1000mm. Compared with the same period of the year, the southern part of the Shanxi-Shaanxi section, the Sanhua section, the most of the Jingwei Luo River and the downstream area are more than 8 to 2.1 times. The daily precipitation of 79 stations in the whole basin exceeds the historical extreme value of the month, of which 77 stations are concentrated in the middle reaches. Sep mid to to the middle and lower reaches of the dense occurs between 3 to a large scale in the precipitation process. With all the year round, compared to the same period upstream Qingtongxia River basin, middle-South and downstream bias in favor of more than 1 times where Sanmenxia reservoir following bias in favor of 3.0~5.8 times. In the context of next week (October 14-21), Yellow River basin has 2 times to be light precipitation weather process respectively 14-15 and 27th before and after are rain mainly. The cumulative precipitation is 5~10mm, of which 10~20mm in the basin above Lanzhou and the southern part of the Jingwei River Basin. The cumulative surface rainfall is 1~10mm. In view of the large amount of precipitation in the early stage, especially in the Lanto (Lanzhou to Tuo County), Shanshan (Shanxi to Shaanxi), Jingwei Luo River, Sanhua (Sanmenxia to Huayuankou) and downstream, the soil is highly supersaturated, the ability to resist floods is significantly weakened, geological disasters occur frequently, coupled with the large flow and high water level of the middle and lower reaches of the Yellow River, and the reservoir regulation capacity is limited. Meteorological experts suggest: 3. Pay attention to small and medium-sized river floods, mountain torrents, geological disasters and urban and rural waterlogging that may be caused by continuous precipitation in the middle and lower reaches of the Yellow River Basin, strengthen monitoring and analysis, update rain and forecast information on a rolling basis, and provide targeted services. According to the forecast of the National Climate Center, the cold air is more frequent in October, and the temperature in the northern part of the middle reaches of the Yellow River is low. It is necessary to pay attention to the adverse effects of strong winds and frost on life, production, transportation, and flood prevention and relief work. In addition, it is expected that from October to December, the equatorial Middle East Pacific sea surface cold water will be further strengthened, or will enter the La Nina state. Under the influence of La Nina, the cold air process may be more frequent, and the middle and lower reaches of the Yellow River need to be vigilant and be ready to fight against Lingxun.

Note: This is auto-translated version of a Chinese domestic news media article. A mature and nuanced reading is suggested.