The water level of Poyang Station in Jiangxi Province has exceeded the historical extreme value 1998. What caused this?

In the past month, there have been seven times of heavy rainfall in the middle and lower reaches of the Yangtze River in China, especially since July 4, when heavy rains have continued along the main stream of the middle and lower reaches of the Yangtze River. Continuous heavy rainfall has brought serious floods to Guizhou, Anhui, Jiangxi and other regions. In Jiangxi, the total rainfall in northern and central Jiangxi has reached more than three times that of normal years. As of July 12, the water levels of four hydrological stations in Poyang Lake, Jiangxi Province have all exceeded the historical extreme value, and the water levels are still rising. Jiangxi Province is facing the most severe flood control situation since June 1998. There are five rivers in Jiangxi: Ganjiang, Fuhe, Xinjiang, Raohe and Hexiu. They all have a similar trend under the influence of surrounding mountains and hills, and flow into Poyang Lake, the largest freshwater lake in China, from east, south and west respectively. After the renovation of Poyang Lake, the surging river flows into the Yangtze River from the mouth of the lake, forming a complete Poyang Lake water system. In the vast area of South China, including Jiangxi, there are two rainy seasons with relatively concentrated precipitation every year, namely, the pre-flood season and the post-flood season in South China. Generally speaking, the pre-flood season in South China is from April to June, and it is the rainy season in South China/KLOC-0. The precipitation in this period is mostly caused by the action of cold and warm air or monsoon onset. July to September is the second rainy season, which is also called the late rainy season in South China. The precipitation in this period is mainly influenced by tropical weather systems such as typhoon and subtropical high. Generally speaking, although the total rainfall in the first flood season in South China is more than that in the second flood season, the precipitation intensity in the second flood season is often stronger and the local disasters caused by it are more serious. At present, the middle and lower reaches of the Yangtze River, including Jiangxi, are in the late flood season. The precipitation in the first flood season mainly occurs in the westerly belt on the north side of the subtropical high. Because of the confluence of cold and warm air currents, the characteristics of frontal precipitation often appear. In the first flood season in June this year, the vast South China experienced five heavy rains. At the end of June, a large-scale heavy rainfall belt has been pulled from the southwest and extended to Jiangsu, Zhejiang and South China. The rain curtain in June has not been closed, and the heavy rain in July has come soon. ? The recent violent rainstorm is inseparable from a major climate phenomenon, that is, El Nino. When El Nino occurs, the earth's atmospheric circulation will be abnormal. Generally speaking, the East Asian summer monsoon is weak this year, and the force of warm and humid air flow northward is not strong. Under the influence of the northwest wind from the inland south, cold and warm air constantly meet in the south. Affected by this circulation situation, such continuous heavy rainfall has occurred in the middle and lower reaches of the Yangtze River, including Jiangxi, since the end of June. Since the beginning of this year, the rainfall in Jiangxi has been 20% higher than normal, and it has been 60% higher since June. Especially since July, the rainstorm caused by disasters in northern Jiangxi has lasted for many days. Of the 3 1 rainfall in Jiangxi this year, 10 heavy rainfall in June alone accounted for half. Under such heavy rainfall, since July 1 1, the water levels of Poyang Station, Kangshan Station, Xing Zi Station and Tangyin Station of Poyang Lake in Raohe, Jiangxi Province have successively exceeded the highest water level in history, and the flood control and disaster relief situation in Jiangxi Province is extremely severe.