Extreme rainstorms and floods in North China have aroused great concern from all walks of life. Reviewing this exceptionally heavy rainstorm and flood, Zhang Jianyun, academician of the Chinese Academy of Engineering, honorary president of the Nanjing Institute of Hydraulic Sciences, and director of the Climate Change Research Center of the Ministry of Water Resources, repeatedly stressed that "we must give the flood a way out and give the flood space." ”
Zhang Jianyun has long been engaged in scientific research in hydrological and water resources, flood prevention and drought mitigation, climate change impact, and water ecological environment governance and protection. After the Zhengzhou Heavy Rainstorm and Flood Disaster in 2021, as the leader of the Zhengzhou "7.20" Heavy Rainstorm Flood Disaster Investigation Expert Group of the State Council, he participated in the investigation and report preparation of the disaster.
"The principle of flood control dispatch in the basin is to minimize losses. For example, one bank of a river is a large city, and the other bank is farmland, and the impact and loss after flood distribution are completely different, so different defense standards are adopted. Zhang Jianyun pointed out in a recent interview with The Paper that the cost of flooding big cities is very large, so it is necessary to protect it; After the flood water receded, it could be replanted with relatively small losses.
In view of the defense process of extremely heavy rainfall in North China, Zhang Jianyun believes that the two cities in Beijing-Tianjin-Hebei province fully reflect the spirit of cooperation in the dispatch of reservoirs and the use of flood storage and detention areas, which is also a cooperation mechanism formed in flood prevention and disaster reduction over the years.
However, Zhang Jianyun also pointed out that this extreme rainstorm and flooding has exposed problems such as the lack of management of mountain flood ditches in North China, the insufficient space for storage and storage in the plain in front of the mountain, the weak drainage capacity of flood storage and detention areas, and the need to improve the early warning and management of flash flood geological disasters, which need to be strengthened in the future.
The following is the full text of the interview:
Historically, it is a typical heavy rainstorm area
The Paper: What do you think of the heavy rainfall in the Beijing-Tianjin-Hebei region? Some say the rainstorm is beyond realization.
Zhang Jianyun: The Beijing-Tianjin-Hebei region is bordered by Yanshan Mountain in the north and Taihang Mountain in the west, which is a typical heavy rainstorm area in the mainland.
You may only remember the "July 21" heavy rainstorm in Beijing in 2012, but there have been many extreme rainstorms in history that occurred in this area. For example, in 1607, a major flood occurred, causing "flooding the capital". The torrential rain of 1801 recorded in history that "the flood in the capital was unprecedented." From dawn to the tenth day, heavy downpours did not matter day and night. The walls and houses inside and outside the city collapsed, injuring many people." In 2012, the maximum hourly rainfall of 110.3mm in Beijing was 110.3mm, which was once in more than a century, and 79 people were killed due to heavy rainfall and flooding. In 2016, heavy rainfall in Xingtai City, Hebei Province exceeded "63.8" and "96.8", a historical extreme, resulting in 25 deaths and 13 missing.
Extreme heavy precipitation occurred along the former sites of the Taihang Mountain and Yanshan Mountain Ranges. Map of the Meteorological Detection Center of China Meteorological Administration
This Beijing-Tianjin-Hebei heavy rainfall is a very extreme weather event. The typhoon carried very much water vapor, and encountered the "high-pressure wall" formed by the combination of subtropical high pressure and continental high pressure, as well as blocked by the Yanshan Mountains and Taihang Mountains, resulting in extremely heavy rainfall in this area. The average precipitation in Beijing was 331 mm, 538 mm in Mentougou District, and nearly 600 mm in Fangshan District, while the average precipitation in Beijing for many years was about 580 mm, so this time it fell more than half a year of rainfall in a few days, and even at the Changping Wangjiayuan Reservoir site the rainfall reached 744.8 mm, exceeding the maximum rainfall of "7.21" (Fangshan 541 mm). The Beijing Meteorological Bureau's call for "the highest rainfall in 140 years" is accurate.
The Paper: What are the extremes of this torrential rain and flood?
Zhang Jianyun: The extreme nature of this torrential rainfall flood is reflected in the fact that, first, the rainfall is very strong, with the largest single station in Beijing reaching 744.8 mm, and the maximum rainfall in Xingtai, Hebei Province being 1003 mm. The 2012 "July 21" rainstorm lasted for a day or less, this time the rain lasted from July 29 to the morning of August 1, nearly three days, and in some places lasted more than three days. Third, the flood is very strong, because the heavy rainfall converges very quickly in the mountainous areas of the western Beijing-Tianjin-Hebei region. For example, at the site of the Lugou Bridge of the Yongding River, the flow increased from less than 1,000 cubic meters per second to more than 4,600 cubic meters per second in less than two hours, and the peak flow of the Zhuma River also reached 6,200 cubic meters per second. As of 24:00 on August 8, 33 people had died in Beijing due to the disaster, 18 people were still missing, and about 1.29 million people were affected. But in general, after the heavy rainstorm on July 21, Beijing has done a lot of infrastructure construction related to flood prevention and drainage, and the impact of urban areas has been significantly reduced.
On July 30, 2023, citizens rode in the rain on Lama Temple Street in Beijing. Xinhua News Agency photo
I personally think that this rainstorm is very extreme, but it is not beyond recognition, because this place has historically been a typical heavy rainstorm area.
There is insufficient space for regulation and storage, and the treatment of mountain floods and ditches still needs to be strengthened
The Paper: After the July 21 rainstorm in Beijing in 2012, what improvements have been made to the city's flood prevention and drainage?
Zhang Jianyun: The casualties and losses caused by the exceptionally heavy rainstorm in Beijing on 21 July were very heavy, and the lesson was very profound, and I think it was a turning point in the flood defense of cities on the mainland.
After the "July 21" heavy rainstorm in Beijing in 2012, on the one hand, the mainland's drainage standards and flood prevention standards were revised, and the design of classification standards was proposed, and the design standards for some key areas and low-lying areas were greatly improved and more targeted. On the other hand, the state and governments at all levels attach great importance to urban infrastructure construction, for example, after "7.21", Beijing has increased the capacity building of drainage and waterlogging and comprehensive emergency response, especially the capacity of waterlogging storage and external discharge has been significantly enhanced, and the construction of sponge cities has also achieved certain results. So generally speaking, after "7.21", Beijing's response to heavy rain and flooding was orderly and effective, which is why the urban area was not greatly affected.
The Paper: What problems have been exposed when the suburbs of Beijing were seriously affected this time?
Zhang Jianyun: The main areas affected by Beijing's heavy rainfall and flooding disasters are Fangshan and Mentougou districts. In fact, due to the obstruction of Yanshan Mountain and Taihang Mountain, this special terrain makes it impossible to get out after water vapor comes in, so it is easy to become a high incidence area for heavy rain, which should be given great attention.
On August 1, on a blocked railway line near Shuiyuzui Village, Mentougou District, Beijing, staff of the Sixth Bureau of China Railway were cleaning up debris on the track and restoring traffic. Xinhua News Agency photo
The problems exposed by this extreme rainstorm and flooding are: First, the management of mountain floods and gullies needs to be strengthened. After the flash flood, the streets of Fangshan and Mentougou urban areas became flood channels, and the floodwaters washed down cars and flooded houses on both sides. We've always stressed the need to give space and outlets for flooding, but these streets are lined with buildings, so I think these houses should be retreated and leave some space. These houses should also have a certain height difference from the street, after the flash flood comes, the street as a river flood is no problem, but it should not affect the lives and property of our people, this should be improved.
Second, there is insufficient space for adjustment and storage. After the flash flood goes from the mountain to the plain, the storage space in the pre-mountain plain is obviously insufficient. There are not enough reservoirs in the mountains, and there is no place for storage and storage in the mountains, and flash floods will definitely go on a rampage, break through the embankments, and destroy a large number of public facilities.
Third, the flood storage and detention area of the Haihe River Basin has a weak drainage capacity compared with other river basins. The Huaihe River flood storage and detention area has a strong drainage system, and the water in the flood storage and detention area can be drained in a few days or a short time, but this flood in Zhuozhou, there are reports that the water in the flood storage area is estimated to take a month to recede, which has too great an impact on the lives of ordinary people.
In addition, this heavy rainfall and flooding also exposed a problem, that is, our rainfall forecasts and flood forecasts are relatively confident, but the early warning and management of flash flood geological disasters still need to be improved.
The principle of flood control and dispatch in the river basin is to minimize losses
The Paper: This time Zhuozhou was seriously affected, and some people believe that there is no control reservoir in the upper reaches of the Zhuma River, is it necessary to build more water conservancy projects to prevent extreme rainfall once in a century?
Zhang Jianyun: The serious disaster in Zhuozhou this time is determined by its geographical location. Zhuozhou itself is in a depression, the water flowing from the Taihang Mountains has to collect here, and there are many rivers flowing through here, the water flows slowly after it comes in, and it cannot be discharged, so the water is accumulated for a long time and flooded more severely.
The upper reaches of the Juma River were originally planned to have reservoirs, but for various reasons they were not built. I personally believe that in the future, it is necessary to build appropriate interception and storage projects upstream, which not only plays an important role in flood control, but also has a shortage of water in this area, and the regulation of water resources is also very important.
The Paper: You are the leader of the State Council's Zhengzhou "7.20" Heavy Rainstorm Flood Disaster Investigation Expert Group, which was mainly a big city, this time it was a suburb of Beijing and a small city such as Zhuozhou.
Zhang Jianyun: The main disaster area of Zhengzhou's heavy rainfall is in the main urban area, but there are also disasters in Xingyang and other townships, and "7.20" exposed that Zhengzhou's urban flood prevention and waterlogging infrastructure is very weak, for example, of the 38 drainage districts in the main urban area of Zhengzhou, only one reached the planned drainage capacity at that time, and the actual drainage capacity of some districts was insufficient to cope with the precipitation once in five years. In addition, there are also outstanding problems in Zhengzhou's emergency management and handling capacity, and the preparation of emergency plans is not scientific and the implementation is not in place. Another prominent problem is that the city's "lifeline" projects such as power supply, water supply and communication have been destroyed, bringing great difficulties to medical treatment, people's daily life, and even directing emergency work.
This time, Beijing has absorbed the lessons of "21 July" and "20 July," and on the whole, it has done a good job in all aspects of emergency response.
The Paper: In recent years, the Beijing-Tianjin-Hebei region has always emphasized coordinated development, do you think it has achieved coordination in flood control?
Zhang Jianyun: In the entire flood defense process, the dispatch coordination of the two cities in the Beijing-Tianjin-Hebei province is still efficient and scientific, and eight flood storage and detention areas have been used successively. Without the use of these flood storage and detention areas, the downstream cities of Langfang and Tianjin will be more seriously affected, so the dispatch of reservoirs and the use of flood storage and detention areas fully reflect the spirit of cooperation, which is also the cooperation mechanism formed by the mainland in flood prevention and disaster reduction over the years.
As for how to dispatch floods and which flood storage area to use, it is decided according to the importance of the object of protection. It is necessary to protect large cities, because the cost of flooding in large cities is very large, and after the flood of farmland recedes, it can be replanted, and the loss is relatively small. Therefore, the principle of flood control and dispatch in the river basin is to minimize losses.
Give the flood a way out and space
The Paper: In recent years, the heavy rainfall in the mainland has shown an increase and strengthening, is it related to climate change?
Zhang Jianyun: There have also been many extreme rainstorms in the history of the Beijing-Tianjin-Hebei region, which are the result of the combined effect of various factors such as atmospheric circulation, water vapor conditions, and topography, and it is difficult to change. But climate change has an impact on water vapour conditions and atmospheric circulation, and I think this needs to be said separately.
Climate change, characterized by global warming, affects monsoon conditions in our country and affects the location and intensity of the Pacific subtropical high. In particular, due to global warming, the atmospheric temperature rises, the water holding capacity increases, and once it reaches saturation, rainfall is large. Therefore, in the context of climate change, the occurrence of heavy rainfall tends to increase and become stronger.
On the other hand, with the urbanization development of the mainland, the urban heat island effect and the rain island effect are constantly increasing. In the "forest" of reinforced concrete, the warm and humid air flow encounters a barrier climb during the upward movement, and the cooling of water vapor also easily leads to precipitation. The development of urbanization has turned the former farmland into asphalt roads and cement squares, which has greatly increased the impervious area of the city, reduced infiltration, and reduced the function of "natural sponge". Underground facilities such as parking lots, shopping malls and sunken overpasses are prone to rainwater accumulation and are also flood-prone areas.
Generally speaking, in recent years, extreme rainstorm events on the mainland have shown an increasing and stronger trend, which has the impact of climate change, and is determined by the geographical location, topographic conditions, underlying surface and other factors of these areas, which is the common result of natural conditions and global warming.
The Paper: What advice do you have for future rainstorm and flood prevention in North China?
Zhang Jianyun: First of all, I want to emphasize that we must give the flood a way out. For example, the treatment of mountain floods in the mountainous areas of western North China should be strengthened in the future, and the construction of urban public infrastructure should give a way out of flooding, even if urban roads are used to undertake flood tasks, there must be a certain distance and gap with residential houses to minimize losses.
Second, give space to floods. I suggest that the relevant departments should speed up the review of the heavy rain and flood events in the Beijing-Tianjin-Hebei region, and calculate clearly how much flood is this extreme rainstorm flood, what is the distribution, and how much storage space is needed in each region. It is necessary to speed up the construction of how much space is left, such as the construction of some wetland parks, usually leisure, and when the flood comes, it will be used as a place for flood storage. In addition, some diversion and storage projects should be planned and built on rivers in the mountainous areas of the west, and some experts have proposed to learn from abroad to build deep projects.
In addition, it is necessary to appropriately raise the construction standards of river embankments and improve the flood discharge capacity. Drainage facilities should be built as soon as possible in the downstream flood storage and detention areas, and the flood distribution areas should be used as soon as they are opened, so as to drain the flood as soon as possible to reduce the impact of secondary disasters.
These are systems engineering, and I believe that relevant planning and demonstration will be studied in the post-disaster recovery process.
Source: The Paper
Process Editor: TF028