Henan encounters rare heavy rains, continuous rainfall in many parts of Europe, high temperature sweeping northwestern United States
Extreme weather highlights the threat of climate change
On July 20, Henan encountered a rare extreme heavy rainfall, causing casualties, property losses, urban waterlogging, farmland waterlogging, mountain torrents, and geological disasters, and the risk of railways, highways, and civil aviation was severely affected.
The disaster is worrying, but also confusing: What is the cause of the heavy rain in Henan?
Extreme weather has recently appeared in many places around the world. Are there any common reasons behind it?
What can we do to face natural disasters?
1 The continental high pressure, the subtropical high pressure in the western Pacific, and the typhoon "fireworks" together caused the extremely heavy rain in Henan
Since July 17, extremely heavy rains have occurred in Zhengzhou, Jiaozuo, Xinxiang, Luoyang, Nanyang, Pingdingshan, Jiyuan, Anyang, Hebi, Xuchang and other places in Henan. The center of heavy rainfall is located in Zhengzhou, and the strongest period is concentrated on July 19-20. .
From 20 o'clock on July 17 to 20 o'clock on the 20th, the process rainfall in Zhengzhou reached 617.1 mm, which is equivalent to the rainfall of the previous year in three days.
This heavy rain in Henan has the characteristics of large accumulated rainfall, long duration, strong short-term rainfall, and outstanding extremes.
Chen Tao, chief forecaster of the Central Meteorological Observatory, explained that various factors such as the subtropical high (subtropical high) in the western Pacific (subtropical high), continental high, typhoon "fireworks" and other factors have collectively caused the continuous heavy rain in Henan, rather than a single factor.
Atmospheric circulation is stable and rainfall lasts for a long time.
According to Su Aifang, deputy director of the Henan Meteorological Observatory, the subtropical high and the continental high remained stable in the Sea of Japan and Northwest China, respectively. This caused the low-value weather system between the two to stagnate and seldom move in the Huanghuai area. Therefore, central and western Henan appeared for a long time. Precipitation weather.
At present, only after the typhoon "fireworks" gets closer to our country, the circulation situation adjusts and the source of water vapor is cut off, and the rain in Henan can stop.
The typhoon was "controlled" remotely, and the water vapor conditions were abundant.
In mid-July, Henan was on the edge of the subtropical high, with sufficient convective and unstable energy; on July 18, Typhoon "Fireworks" formed in the western Pacific and approached my country.
"Although the'firework' has not yet landed in my country, a connected air current is formed between its north side and the subtropical high pressure, and it continues to be transported to my country's Huanghuai area. Under the influence of easterly winds, a large amount of water vapor gathers from the sea to Henan area. The uplift of the local terrain in Shang Henan and the effect of the stable maintenance of the weather system have caused the concentration of heavy rain in Henan this time.” Chen Tao said.
The uplift of the terrain is the cause of the terrain.
Su Aifang said that the special terrain of the Taihang Mountains and Funiu Mountains has an uplifting and convergence effect on the easterly airflow. The heavy precipitation areas are stable and less moving in the western and northwestern mountainous areas of Henan Province. The precipitation in front of the windward slope of the terrain has increased significantly, and the rainfall is more severe. Strong.
The convective "train effect" is also the cause of extreme heavy precipitation.
"Train effect" refers to the fact that multiple storm cells (thunderclouds) pass through the same place one after another, just as different carriages of a train pass through the same track one after another. Intermittent short-term heavy rainfall will eventually lead to local heavy rains or extreme heavy rains. rainstorm.
"Under stable weather conditions, small and medium-scale convections have repeatedly developed in the piedmont area of Funiu Mountain and moved towards Zhengzhou, forming a'train effect', resulting in high precipitation intensity and long duration, leading to local extreme heavy precipitation." Su Aifang said.
2 During this heavy rain, the maximum cumulative rainfall, maximum one-hour rainfall and daily rainfall in Henan Province all exceeded historical extremes
The 400mm isoprecipitation line is an important geographic boundary line in my country, roughly passing through the Daxinganling-Zhangjiakou-Lanzhou-Lhasa-Himalayas southeast section, which is the boundary between the semi-humid and semi-arid regions of my country.
Henan is located in the region of the 400mm-800mm isoprecipitation line, which means that it has insufficient rainfall and relatively insufficient rainfall.
Historically, Henan was mainly threatened by drought, with more droughts than rain and waterlogging.
However, under the influence of monsoon climate, precipitation in Henan is unevenly distributed in time and space, and heavy rainfall also occurs in summer, accounting for about half of the annual precipitation.
At present, Henan is just under the dual influence of the rainy season and the typhoon season in North China.
From 16:00 to 17:00 on July 20, the rainfall in Zhengzhou reached 201.9mm in just one hour, exceeding the historical extreme value of hourly rainfall in mainland China.
Coincidentally, the previous extreme value also occurred in Henan: on August 5, 1975, in Linzhuang, Henan, the hourly rainfall was 198.5mm.
Since the founding of the People's Republic of China, Henan has experienced five heavy rainfall processes across the province, of which the "75·8" torrential rain in 1975 was the most violent.
According to Zhang Juan, a meteorological analyst at China Weather Network, from August 5 to 8, 1975, affected by Typhoon 7503, the rainstorm center of Henan Province had a 6-hour rainfall of 830.1 mm in Linzhuang, Biyang County, and a 24-hour rainfall of 1060.3 mm for 3 days. The rainfall is 1605.3mm.
"By comparison, it can be seen that the province’s maximum cumulative rainfall, one-hour maximum rainfall, and daily rainfall during this heavy rain all exceeded the extreme values, which were all greater than the above five processes; the maximum daily rainfall and the maximum 6-hour rainfall, then Second only to the '75·8' process." Su Aifang said that in accordance with the Henan Province local standard rainstorm process meteorological intensity assessment specifications, comprehensively considering the number of days, the process range, the maximum daily rainfall and other indicators, the intensity of the rainstorm process reached "extraordinarily strong "grade.
Some people say that this heavy rainfall in Henan is a "once in a thousand years". Is this statement accurate?
Chen Tao said that the "one encounter in a thousand years" and "one encounter in a hundred years" originated from an interpretation in hydrometeorology, and it was measured with the historical return period of extreme flood events as the cycle.
This rainstorm hit, and it is difficult to make such a judgment until the meteorologists have not obtained reliable, long-term records.
"From the perspective of atmospheric science research, my country only had a relatively accurate and complete scientific record of rainfall after the 1950s. Up to now, the entire rainfall record has been around 70 years." Chen Tao said, " The "one-in-a-millennium encounter" is to estimate a certain type of weather event based on a long historical record, or to express the extremeness of the weather through a statistical method of percentage, which needs to be based on rigorous meteorological records.
3 The frequent occurrence of extreme weather events around the world is closely related to climate warming
Looking back in history, there are many records of extreme weather and climate in both Chinese and Western civilizations.
Since the beginning of this year, extreme weather and climate events around the world have occurred more frequently, with record-setting rainstorms, cold waves and unusually hot weather one after another.
One side is extremely high temperature.
At the end of June this year, historically rare high temperatures swept across the northwestern United States and southwestern Canada, killing hundreds of people.
The states of Washington, Oregon, and California in the United States broke historical records on a large scale. The highest temperatures in Seattle and Portland once reached 42 degrees Celsius and 46.1 degrees Celsius, breaking records significantly.
The temperature in Leiden, a small town in British Columbia, Canada, even reached 49.56 degrees Celsius, which was more than 10 degrees higher than the local average temperature.
It is worth noting that Seattle, Vancouver and other places have always been known as "moderate and livable", the temperature is not high or low, and the average summer temperature usually does not exceed 30 degrees.
Meteorological experts said that this high temperature is really rare.
"This heat wave is caused by the turbulence of the westerly belt and the subtropical high in North America: the westerly jet, which was supposed to move from west to east, suddenly oscillated violently and turned into a north-south movement; it was supposed to stay in Hawaii’s Pacific subtropical high and suddenly jumped onto North America. The West Coast is developing strongly.” Some media published an article.
On the one hand, heavy rains continue.
In recent days, continuous heavy rains in many parts of Europe have caused floods and destroyed a large number of houses and roads.
Up to now, more than 100 people have been killed in the floods.
In western Germany, the most affected region, floods caused by downpours caused at least more than 100 deaths, and about 1,300 people were still missing.
The report entitled "Extreme Summer: Floods, Heat and Fires" recently released by the World Meteorological Organization pointed out that parts of Western Europe experienced two months of rainfall during the two days from July 14 to 15.
German Chancellor Angela Merkel stated that the damage caused by the floods was "surreal" and "this is shocking-I can almost say that there is no word in German that can describe this disaster."
According to a report by the Japan Broadcasting Association on July 10, parts of southwestern Japan are facing the strongest rainstorm in decades. The Japanese government has issued evacuation requests to more than 120,000 residents in some southern counties.
From July 4th to 12th, the cumulative rainfall observed in Tottori and Shimane prefectures in Japan has reached twice the average rainfall of the entire July. The short-term cumulative rainfall in Sakaiminato City and Izumo City both hit the record since statistics. New high record.
Frequent extreme weather around the world is closely related to climate warming.
The Secretary-General of the World Meteorological Organization Petri Talas stated that climate change is the root cause of the torrential rains and floods that have swept through Western Europe this summer. Before the mitigation of climate change is effective, there will be more and more extreme weather events and natural disasters.
"If there was no climate change, people would not have observed such high temperatures in the western regions of Canada and the United States. This is a clear sign of climate change." Talas said.
"Every 1 degree Celsius of the earth’s atmosphere warms up, it can absorb 7% more water vapor and form precipitation in the future." Stefan Ramstorf, a professor at the Potsdam Institute for Climate Impact Research in Germany, said that the measurement data has been confirmed, including In the mid-northern latitudes of Germany, the number of days of light rain is decreasing, while the number of days of heavy rain is increasing.
Carl-Friedrich Schlausner, head of the research team at the Institute of Geography of the Humboldt University in Berlin, believes that in 2021 there is no need to doubt whether “climate change can contribute to meteorological disasters”. The question is how much of this impact is. .
"We know that (global) warming will lead to an increase in heavy rains, which in turn will lead to more frequent and destructive flooding events."
Lamia Messari-Becker, a professor of architecture at the University of Siegen in Germany, said that years of research have shown that extreme weather can occur faster, more intense, more frequent, and more concentrated.
Climate adaptation is as important as climate protection. People must improve the early warning system of urban drainage and meteorological disasters to ensure the endurance of critical infrastructure under extreme weather.
4 The formation mechanism of extreme weather is complicated. It is necessary to strengthen the level of early warning and forecasting, but also to make up for shortcomings in disaster prevention and mitigation.
Weather, meteorology, and atmosphere are a highly chaotic system. Even the smallest changes may cause unpredictable disturbances to the atmospheric motion itself.
This is exactly the difficulty of climate prediction.
On July 21st, at a press conference held by the China Meteorological Administration, Chen Tao said, “Extreme rainstorms and extreme high temperatures are still common problems faced by the world. The formation of this scientific mechanism of extreme weather is very complicated, and then it is implemented in numerical forecasting. There is still a lack of effective means to solve this problem. This is a difficult problem that the scientific community is starting to overcome.
In weather forecasts, rainstorm forecasts are recognized as a worldwide problem.
"The accuracy of rainstorm forecasts in developed countries is probably between 20% and 25%. Compared with other countries that are more advanced in forecasting, my country has more mountains and hills, more complex terrain, and more complex geographic environments. Therefore, forecasting It's even more difficult." Ma Xuequan, chief forecaster of the Central Meteorological Observatory, said.
At present, the 24-hour typhoon track forecast error in my country has been reduced to about 70 kilometers, the 24-hour rain forecast accuracy rate has reached 88%, the 24-hour rainstorm forecast accuracy rate is about 20%, and the short-term approaching rainstorm warning accuracy rate has increased to 89%. , The accuracy of rainstorm forecast is at the same level as that of the world's powers.
In addition, the addition of modern satellites, radars and other high-tech means, and the application of modern supercomputers have greatly improved the accuracy of weather forecasts.
Faced with the shortcomings exposed by localities in responding to extreme weather, Wang Wei, Director of the Technical Information Division of the Department of Flood and Drought Prevention of the Ministry of Water Resources, said frankly that from the perspective of early warning and forecasting, some rivers in the north have short and rapid floods and short flood forecast periods. Insufficient data and inadequate forecasting capabilities; mountain flood disasters and flood monitoring and forecasting levels of small and medium-sized rivers also need to be improved.
From the perspective of dispatching, some rivers and water projects' flood control dispatching plans, over-standard flood prevention plans, and reservoir flood season dispatching operation plans are not perfect; most of the basin water project disaster prevention joint dispatching is still in the exploratory stage, and flood control, water supply, The multi-objective dispatching mechanism of ecology, power generation, shipping, etc. is not yet perfect, and the degree of informatization and intelligence of dispatching needs to be improved.
"In addition, some river basins have not experienced major floods for many years. A small number of cadres and the masses have insufficient knowledge of the disasters of torrential rains and floods, and lack practical experience in flood prevention and flood fighting. The awareness and ability of disaster prevention and avoidance need to be enhanced." Wang Wei pointed out.
At present, my country has initially established a relatively complete hydrological monitoring, forecasting and early warning business system, which provides strong technical support for the national command and decision-making for flood prevention, drought relief and disaster reduction.
The areas involved in extreme rainstorms and obviously strong convective weather are facing a major examination of the public safety system. The focus of the examination is undoubtedly to make up for the shortcomings of disaster prevention in the region-where there are weak links or security loopholes, sudden emergencies are prone to occur. Happening.
On the other hand, for the early warning and forecast of extreme weather, the early warning department should also ensure the timely and accurate delivery of early warning information through different channels such as WeChat, Weibo, and SMS, and release relevant science content on disaster prevention and avoidance to the public.
Only by taking precautions, strengthening early warning, and preparing for it, can we better respond to extreme weather and reduce the adverse effects of climate change.
Our reporter Li Yunshu Chai Yaxin