Why is there drought in the middle and lower reaches of the Yangtze River? Great gods, help!

Core Tip: Since June 65438+ 10 this year, the precipitation in the middle and lower reaches of the Yangtze River has obviously decreased, and there has been a severe drought since June 1954 had a complete meteorological observation record. According to the latest weather forecast, in the coming week, the meteorological arid areas in the middle and lower reaches of the Yangtze River will be dominated by sunny and hot weather with little rain, which may lead to the persistence and development of drought. The middle and lower reaches of the Yangtze River continue to suffer from drought. On May 24th, Zhou Bing, a researcher at the National Climate Center of China Meteorological Bureau, said in an interview that since June 5438+ 10 this year, the precipitation in the middle and lower reaches of the Yangtze River has obviously decreased, and there has been a severe drought since June 5438+0954, which can be said to be an extreme climate event. According to the latest weather forecast, the weather in the middle and lower reaches of the Yangtze River will be mainly sunny and hot with little rain in the coming week. The precipitation along the Yangtze River is less than10mm, and the daily maximum temperature will be between 32℃ and 36℃. High temperature and lack of rain may lead to the persistence and development of drought. Climate monitoring shows that from June 65438+1October 65438+1October to May 23, the precipitation in most parts of the middle and lower reaches of the Yangtze River is 30% to 80% less than normal. The average precipitation in Anhui, Jiangsu, Hubei, Hunan, Jiangxi, Zhejiang and Shanghai is 1954, the lowest since. The continuous lack of rain has led to abnormally low water levels in rivers and lakes, significantly reduced water area, affected agricultural production, and difficulties in drinking water in some areas. According to meteorological satellite remote sensing monitoring, the flow of the main stream of the Yangtze River is 25% to 70% less than normal. On May 20th, the water area of Dongting Lake decreased by about 73% compared with the same period of last year. The latest drought monitoring shows that there are moderate to severe meteorological droughts in southeastern Hubei, central Anhui, southern Jiangsu, northeastern Hunan, northwestern Jiangxi, northern Zhejiang and northwestern Guizhou. Seize favorable weather conditions and carry out large-scale artificial precipitation enhancement operations. From May 2/KLOC-0 to the morning of the 23rd, rainfall occurred in the middle and lower reaches of the Yangtze River. The cumulative precipitation in eastern and southwestern Hubei, northern and western Hunan, central and northern Jiangxi, southern Anhui and central and northern Zhejiang is 30-50 mm, and the precipitation in southeastern Hubei and northwestern Jiangxi is 60-90 mm. In order to increase rainfall and alleviate the drought in the middle and lower reaches of the Yangtze River, meteorological departments at all levels seized the favorable weather conditions during the rainfall and carried out large-scale precipitation enhancement operations in the air and on the ground. According to statistics, from 8: 00 on May 2/KLOC-0 to 8: 00 on May 23, Hubei, Hunan, Jiangxi, Anhui, Jiangsu and Zhejiang * * * carried out 334 weather modification ground operations, which played a good role in increasing rainfall. Meteorologists pointed out that there must be cloud formation and precipitation weather conditions for artificial precipitation and snow enhancement; In order to achieve good results, the cloud must meet certain conditions, such as the thickness of the cloud should be above 2000 meters, the height of the cloud bottom should be below 2000 meters, and the water vapor transported from the cloud to the cloud should be sufficient. This rainfall is conducive to improving soil moisture in the middle and lower reaches of the Yangtze River, but the increase of water storage in reservoirs and lakes is not obvious. There are three reasons for the drought. Through preliminary analysis, the National Climate Center believes that the main reasons for this drought are as follows: First, the atmospheric circulation system affecting the eastern part of China is extremely significant. At present, the subtropical high in the western Pacific (10. 15, 0.0 1, 0. 10%) is stronger in the north than the multi-year average, and the western ridge is west. There is an anticyclone abnormal circulation in the middle and lower troposphere, which causes no precipitation for a long time and less precipitation, thus forming drought. Due to the influence of subtropical circulation system in previous spring, there will be long-lasting continuous rain in Jiangnan area in spring. Secondly, the water vapor transport conditions are insufficient, and the water vapor channel cannot be effectively established. At the turn of spring and summer, with the development of tropical convection system and the outbreak of summer monsoon in the South China Sea, there are usually three channels that affect China's water vapor-Somali cross-equatorial southwest airflow, Bay of Bengal cross-equatorial southwest airflow southward, and southwest airflow from the South China Sea and its eastern vicinity, but the water vapor transport in the three channels is generally weak. According to the analysis and diagnosis of the water vapor budget of the whole troposphere in the arid area of the middle and lower reaches of the Yangtze River by the Climate Monitoring Office of the National Climate Center, the water vapor loss in this area was large in May, and there was a lack of material conditions for precipitation. In addition, since the beginning of this year, the cold air activity has been remarkable and powerful, and it is impossible for the middle and lower reaches of the Yangtze River to form a situation of cold and warm convergence. According to the cold air monitoring results of the National Climate Center, from June 5 to April this year, the cold air affecting the eastern part of China was nationwide, with strong force, which was not conducive to the northward advancement of tropical systems. Even if there is a drought, we should be prepared for flood control. Does the continuous drought mean that the flood control situation in the Yangtze River will be eased this year? Zhou Bing believes that, in terms of climate, the middle and lower reaches of the Yangtze River generally enter Mei in mid-June, and there will be many rainstorms during the Mei Yu period, which will bring a lot of rain. At present, there is still a period of time from plum blossom in the climate sense. Although there are signs of drought during this period, the annual variation of plum blossom season is great. Therefore, while fighting drought with all our strength, the flood control in the Yangtze River basin should not be taken lightly. Zhou Bing introduced that in the future, the flood control and drought relief situation in the Yangtze River may coexist with drought and flood, and the summer drought and high temperature heat wave in the Yangtze River basin should also be highly valued; We must pay close attention to the changes and changes in the circulation situation. Once it becomes a stable atmospheric circulation system conducive to precipitation or a rainy season situation, precipitation may increase rapidly. "By analyzing historical data, we found that droughts and floods in other parts of China turned sharply or reversed in history. Therefore, on the one hand, we should do a good job in drought relief, on the other hand, the flood control situation should not be underestimated, and we should pay close attention to it. " Zhou Bing stressed. Meteorologists also pointed out that there is relatively much rain in southwest and south China, and all relevant departments should strengthen their defense against the adverse effects of strong convective weather such as mountain torrents, geological disasters, urban and rural waterlogging, lightning, strong winds and hail that may be caused by local heavy precipitation.