What is the difficulty of rainstorm forecast

　　Our reporter Guo Jingyuan

　　Since July 17, Henan Province has experienced extreme heavy rainfall, which is rare in history, and the daily rainfall of more than 10 national meteorological observatories has reached the historical extreme value since meteorological observation records.

From 8:00 on the 17th to 13:00 on the 22nd, the cumulative rainfall in the north-central part of the province reached 200 mm to 400 mm, of which the local areas of Zhengzhou, Hebi, and Xinxiang exceeded 900 mm.

Someone vividly said that Zhengzhou, which has become the center of the extreme heavy rain, has given up all the rain for a year in one day.

　　As we all know, our country is a country with heavy rains.

The summer monsoon comes from the sea according to its inherent laws, transporting abundant water vapor to most areas of China, and providing sufficient "fuel" for the occurrence of heavy rainfall and strong convective events.

At present, the earth’s climate is undergoing tremendous changes, and heavy rain events are both a hot and difficult issue in the field of global atmospheric science research.

In the face of violent rainstorms, a detailed study of its causes requires sustained research.

The reporter interviewed Li Zechun, an academician of the Chinese Academy of Engineering, Luo Yali, a researcher at the Chinese Academy of Meteorological Sciences, and Chen Tao, the chief forecaster of the Central Meteorological Observatory, to explore the storm forecast problems that plague the global meteorological community.

　　The cause of rainstorm in Henan is special

　　A rainstorm is complicated and can be analyzed from different angles and levels.

According to the 50mm standard, whether the rainstorm rains evenly within 24 hours or pours down in a short period of time, not only gives the public a different perception, but also has different impacts on social operation and safety production. It is still different in the city under heavy rain. The countryside will also lead to very different consequences.

　　Chen Tao introduced that since July 17th, the heavy rainfall in Henan has accumulated a large amount of rainfall, a long duration, concentrated precipitation areas, and the extreme characteristics of hourly rainfall are also very obvious.

Among them, 201.9 mm exceeds the extreme value of the hourly rain intensity since the meteorological record of mainland China.

　　"Such rain intensity is extremely extreme in the world." Luo Yali was at a review meeting when he learned of the heavy rain in Henan, and this explosive news quickly became a topic of concentration among the scientists present.

She said that although for forecasters and meteorological researchers, the circulation situation that formed this heavy rain is generally clear: the western Pacific subtropical high and the continental high are maintained stably, and the typhoon "fireworks" that is still on the ocean is moving forward. Our country transports abundant water vapor in the process of approaching, coupled with the influence of the special terrain of the Taihang Mountains and Funiu Mountains, but it is obvious that further digging is needed to clarify the mechanism.

　　The extreme rainstorm in Henan this time is different from other extreme heavy rainfall events in other places before. "The high and low latitude circulation situation is coordinated. The typhoon "Fireworks" is still on the ocean surface and the intensity is not weak. The water vapor transmission capacity is very strong, and the terrain is like one. The'anchor' stabilizes the updraft.” Luo Yali also noticed the particularity of the underlying surface of Zhengzhou, a large city. “The city is a relatively new underlying surface type, which makes the ground heat more powerful, and in areas with sufficient water vapor Under circumstances, it is likely to increase precipitation, which will also reduce the water seepage capacity and become more vulnerable to extreme precipitation."

　　"From the perspective of weather, a very heavy rainstorm must not only have very abundant water vapor, but also have a strong vertical upward movement to turn the water vapor into large droplets and fall down, and it must be coordinated with various weather conditions around it." At that time, the Central Meteorological Observatory. Li Zechun, the leader of the forecast team, recalled that from August 5 to 8, 1975, Typhoon "7503" traveled northward after passing through Fujian, Jiangxi, and Hunan, passing through Hubei, and stagnating in Henan, resulting in a rare heavy rain and flood in history— —A total of 1631 millimeters of rainfall fell in southern Henan in 3 days.

　　Complexity beyond imagination

　　No matter how difficult it is, the rainstorm forecast is a "must answer."

"Storm and floods are one of the most common and serious natural disasters in our country. They have a direct and serious impact on people’s life safety, economic and social development, and national security. Moreover, our country’s torrential rain disasters spread across the country’s north and south, urban and rural areas. Large-scale basin floods, as well as disasters caused by small and medium-scale local rainstorms, and extreme rainstorms frequently occur." Li Zechun said.

　　"Over the years, thanks to the development of increasingly perfect meteorological observation systems, high-resolution numerical model forecasting systems, and the commercial application of many advanced scientific research results, my country's rainstorm research and forecasting have continued to make progress." Li Zechun pointed out, but in essence The chaotic nature of atmospheric motion determines that weather forecasts will inevitably have a certain degree of error. At the same time, the formation mechanism of heavy rain due to its locality, suddenness and variable activity rules has not been thoroughly studied so far, and it is still the world A difficult problem in the field of meteorology.

It is even more difficult to forecast extreme rainstorms exceeding 200 mm in an hour.

　　The main means of forecasting heavy rain in my country is to use numerical weather forecast model products and combine the knowledge and experience of forecasters themselves.

In recent years, although the resolution of numerical weather prediction models has gradually increased, generally speaking, the probability of extreme events is very small.

The study found that although the general circulation situation is stable and clear when some extreme rainstorms occur, there must be small and medium-scale convective systems that have an effect. The scale may only be one or two hundred kilometers, and the life cycle is only a few hours. The current numerical prediction model It is difficult to express it accurately and clearly.

　　Continue to tackle forecasting problems

　　The research and forecast of rainstorms has always been one of the main targets of my country's meteorological workers.

As early as the beginning of the 20th century, Chinese scientists began to study rainstorms. After nearly a hundred years of development, significant progress has been made in rainstorm theory, rainstorm analysis and forecasting.

　　For example, during the "75·8" rainstorm, the Chinese Meteorological and Hydrological Departments learned lessons from this rainstorm and other unprecedented heavy rains and floods, and strengthened research on heavy rains at the national level. The research on heavy rains has also been gradually shifted from the weather scale to the middle. The scale, and then the heavy rain forecast changed from empirical qualitative to quantitative.

　　In addition to the improvement of numerical models and the development of objective forecasting methods, another focus on the accurate improvement of rainstorm forecasting capabilities and fine services has been placed on forecasters like Chen Tao who have been "nailed" to the duty room for a long time.

Of course, they not only exist as business personnel, but also scientific researchers.

Chen Tao believes that at this stage, expert forecasters need to have a keen and profound insight into the process of rainstorm formation, analyze and forecast key influence systems from massive observations and forecast information and their correlation with the time, location, and precipitation of future rainstorms, so as to detect early Weather system forecasting deviations, condensing key forecast factors, and relying on various modern forecasting technologies to finally form correct forecasts for major rainstorms.

Faced with the scientific problem of heavy rain, practitioners in the meteorological research department and atmospheric science research experts and scholars will work closely with each other, and continue to tackle the problem through technological innovation and development.

　　In recent years, Li Zechun has also been very concerned about popular science for the public and decision-makers.

Disaster prevention and mitigation are inseparable from weather, and ordinary people cannot do without weather.

He hopes that by continuously improving the scientific literacy of the people, strengthening the awareness of disaster prevention and mitigation and improving the ability of decision makers, and having a deeper understanding of how to make rainstorm forecasts, where the difficulties are, and how much risks are, in order to make better use of weather forecasts and early warnings. Preparation and arrangement.