Home » Record-breaking heavy rainfall in many places faces challenges in disaster prevention and mitigation

Record-breaking heavy rainfall in many places faces challenges in disaster prevention and mitigation

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Record-breaking heavy rainfall in many places is facing challenges in disaster prevention and mitigation

Behind frequent extreme weather

On the evening of August 16, local heavy rainfall occurred in Haidian District, Beijing. The accumulated precipitation in one hour exceeded 80 millimeters. A car passed under the Hanhe Road Railway Bridge and was trapped. Unfortunately, two people in the car were killed. Witnesses said that the sudden heavy rain formed severe water accumulation in a short period of time. Many vehicles were flooded over the roof of the car at the scene, and the deepest water level was close to two meters. A few days ago, 21 people were killed and 4 people lost contact due to extreme rainfall in Liulin Town, Suixian County, Hubei Province.

Following the heavy rains in Henan in late July, many places have recently faced severe flood risks. According to forecasts by the Ministry of Water Resources, over-alarm floods may occur in the middle and late August of the middle reaches of the Yellow River, parts of the Haihe River, and the upper and middle reaches of the Yangtze River. Typhoon rainfall may trigger regional rainstorms and floods. The flood control situation is not optimistic. Including heavy rainfall, this year’s extreme weather has occurred frequently and caused complex causes, and its background is more related to climate change. The severe challenges faced by urban planning and disaster prevention and relief emergency systems should be focused on.

1 The combined effect of multiple factors has resulted in extremely heavy rainfall, which has obvious characteristics of continuous, wide area, and strong spot, which is relatively abnormal compared with the same period of normal years.

my country is a country with heavy rains. The summer monsoon from the tropical and subtropical oceans northward transports abundant water vapor to most of China. However, the current frequent extreme heavy rainfall events in many parts of our country are rare since the meteorological records.

The Sui County Government of Hubei Province issued a notice on August 13th. From 21:00 on the 11th to 9:00 on the 12th, Liulin Town had accumulated 503 mm of rainfall in 12 hours; the rainfall reached 373.7 mm from 4 to 7 on the 12th. Rainfall exceeded 100 mm for two consecutive hours at 6 o’clock. The township of Liulin Town is surrounded by mountains on three sides. The average depth of water during the disaster was 3.5 meters, and the deepest point was 5 meters. Although the stagnant water has receded, rescue work is still advancing intensely.

The scale of this torrential rain exceeded many people’s expectations. From 16:00 on August 11 to 16:00 on the 12th, 16 meteorological monitoring stations in Hubei province monitored extremely heavy rain, and 166 meteorological monitoring stations monitored heavy rain. The Hubei Meteorological Bureau also upgraded the emergency response of major meteorological disasters (heavy rain) from Level IV to Level III, reminding to strengthen prevention of flooding in small and medium-sized rivers, mountain torrents, geological disasters and urban and rural waterlogging caused by continuous precipitation, and to do a good job in monitoring the water and rain conditions of small and medium lakes, reservoirs, weirs and ponds. And safety management.

Chen Xuan, chief forecaster of the Wuhan Central Meteorological Observatory, explained that the heavy rainfall was mainly affected by the dynamics of the high-altitude short-wave trough, with the stability of the low-level vortex and the easterly jet in the boundary layer, and it occurred under the influence of the increase in topography.

On August 12, the Central Meteorological Observatory upgraded and issued a yellow warning of heavy rain. It is expected that the rainfall from the east of the southwestern region to the middle and lower reaches of the Yangtze River will enter the strongest stage from the 12th to the 13th, and it will last for a week.

“The current rainfall process starting on the 9th has a certain relationship with the adjustment of atmospheric circulation.” Chen Tao, chief forecaster of the Central Meteorological Observatory, said that the current position of the subtropical high is significantly souther than the previous period, and the warm and humid air at the edge of the subtropical high has the same force as the mid-latitude cold air. , And continue to converge in the middle and lower reaches of the Yangtze River, the weather characteristics are similar to the Meiyu weather.

The cold and warm air forces have caused the rainband to move slowly, coupled with abundant water vapor, unstable convection, and sufficient energy, the local short-term heavy rainfall has obvious characteristics. Chen Tao believes that extreme rainfall occurs at local sites, which is relatively abnormal compared to the same period in normal years.

Around July 20, Zhengzhou, Henan and other places had the rain of the previous year in three days, which is a concrete manifestation of an abnormally heavy rainfall event.

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Jia Xiaolong, deputy director of the National Climate Center, believes that the abnormal synergy of East Asian atmospheric circulation is the direct cause of extreme heavy rainfall in many places. “Recently, the western Pacific subtropical high has been stronger and northerly, extending to the east of North China and the east of Huanghuai area in the west. Henan is at the western edge of the subtropical high and has sufficient convective and unstable energy. At the same time, typhoon activities in tropical areas have entered a period of frequent typhoon activity, which has strengthened from the northwest. The water vapor transport in the Pacific Ocean, the South China Sea and the Bay of Bengal provides abundant water vapor sources for heavy rainfall in Henan.” Jia Xiaolong said that the strong subtropical high pressure in the western Pacific and the continental high pressure in Central Asia have stabilized the atmospheric circulation and further extended Henan and other places. Duration of heavy rainfall.

2 Global warming will inevitably lead to an increase in precipitation, and climate change is the root cause of increased extreme weather instability

This year, both in China and other parts of the world, the frequency and intensity of extreme weather events have increased significantly.

In Europe, countries such as Germany and Belgium suffered floods, killing nearly 200 people. In North America, rare heat waves swept through the United States and western Canada, killing hundreds of people. At present, many countries in North America and Europe are still suffering from wildfires, and even some areas that have been shrouded in cold all year round have not been able to escape. In Yakutia, one of Russia’s coldest regions, eastern Siberia, wildfires that have continued for several weeks have turned 3.4 million hectares of frozen soil into scorched earth.

Many foreign experts attribute the frequent occurrence of extreme weather around the world to climate change. “Humans are not unfamiliar with extreme weather, but climate change has undoubtedly increased the frequency and severity of extreme weather.” The Secretary-General of the World Meteorological Organization Petri Talas recently stated that extreme weather events will take effect before climate change mitigation is effective. And natural disasters will increase.

“Global warming has aggravated the instability of the climate system, which is the root cause of the frequency and intensity of extreme weather events.” Jia Xiaolong also believes that with the warming of the climate, the atmosphere can hold more water vapor before it becomes saturated. The possibility of precipitation has increased.

When it rains, cumulonimbus clouds are needed. Clouds are formed by the rising and condensing of water vapor, and water vapor needs to be heated when it evaporates. In other words, the hotter the weather, the more cumulonimbus clouds and the more rain. Scientific research shows that for every 1°C increase in the average temperature of the earth, there will be 7% more water vapor in the atmosphere. These water vapor will fall back to the ground in the form of rain in summer, and appear in the form of snowfall in winter, leading to severe weather such as torrential rain and blizzard.

The China Meteorological Administration announced the “China Blue Book of Climate Change (2021)” at a press conference held on August 4, stating that the comprehensive observations of the climate system and a number of key indicators indicate that the climate system is still warming and the risk of extreme weather and climate events Intensified further.

According to Chao Qingchen, deputy director of the National Climate Center, the annual report of the Blue Book of Climate Change in China has been released every year since 2011. During the compilation of the Blue Book, a large number of observational data and basic data provided by the Ministry of Natural Resources, the Ministry of Water Resources, and the Chinese Academy of Sciences were used.

The Blue Book pointed out that from 1951 to 2020, the annual average surface temperature in my country showed a significant upward trend, with a temperature increase of 0.26 degrees Celsius every 10 years. At the same time, the average annual precipitation in my country from 1961 to 2020 shows an increasing trend, with an average increase of 5.1 millimeters every 10 years, especially in the eastern part of the Yangtze River, the northern part of the Qinghai-Tibet Plateau, the northern part of Xinjiang, and the western part.

“The past 20 years have been the warmest period since the beginning of the 20th century. Among the 10 warmest years since 1901, the remaining 9 years were in the 21st century except 1998.” Chao Qingchen said when interpreting the blue book that my country is the world In the sensitive areas and significant impact areas of climate change, the rate of temperature increase is significantly higher than the global average during the same period.

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In the context of current global climate change, the environmental conditions of all extreme weather and climate events are also changing to varying degrees, and all weather systems and the location and intensity of storms are also changing. In January this year, the large-scale severe cold wave weather occurred in the central and eastern part of our country, and the current extremely heavy rains in many places belong to this situation. Wang Zhihua, spokesperson of the China Meteorological Administration and director of the Department of Emergency Mitigation and Public Services, said that the record-breaking extreme events that occur now will become frequent events as the climate warms, which is the “new normal” for the future climate.

3 Some changes such as global sea level rise are irreversible, and the climate crisis may exceed human adaptive capacity

The impact of climate change has always been a key issue internationally. The sixth assessment report of the United Nations Intergovernmental Panel on Climate Change (IPCC) released on August 9 “Climate Change 2021: Natural Science Foundation” shows that human activities are changing the climate in unprecedented and even irreversible ways. If mankind does not take measures, climate change in all regions of the world will intensify in the next few decades, and extreme heat waves, droughts and heavy rainfall events will become more frequent.

According to the 3,500-page report, human activities have caused the global temperature to rise by 1 degree Celsius compared with the pre-industrial era, and it is now rapidly approaching 1.5 degrees Celsius, which is the warning line established by the Paris Agreement. Even if global carbon emissions have fallen sharply from today, the temperature increase will still exceed the 1.5 degrees Celsius mark, and it will take a while to stop rising and turn down.

Small fluctuations in climate values ​​will have a major impact on the world. Since the 1950s, heat waves and torrential rains have become more frequent, and their intensity has continued to break through extreme values, affecting Europe, North America, Africa and most of Asia. The drought that occurred once every 10 years in the past has now increased by 70%, and the number of hurricanes has increased by 66%.

This report also mentioned that some of the effects of climate change may be reversible, for example, the temperature can be lowered. But there are also some changes that are irreversible for thousands of years, such as changes in sea level, Arctic sea ice, frozen soil, mountain glaciers, and polar ice caps.

Take the rise of sea level as an example. The ocean area accounts for two-thirds of the world. When the global temperature rises, the water body will expand. In addition, the melting of glaciers and ice caps, the melting of frozen soil, and the reduction of seasonal snow cover will cause the sea level to continue. rise. Melting ice sheets are difficult to recover, so the effects of sea level rise are irreversible for thousands of years.

Professor Zhang Xuebin of the Canadian Ministry of Environment and Climate Change, who participated in the writing of the report, said in an interview with the media that the increasing frequency and intensity of global extreme weather events may exceed human adaptability.

For example, the extreme heat wave that occurred once every 50 years in the past will now occur once every 10 years; if the temperature increase reaches 1.5 degrees Celsius, the 10-year cycle will be shortened to 5 years; if the temperature increase exceeds 4 degrees Celsius, then every 15 humans I will experience a climate nightmare that I experienced only once or twice in my entire life.

The terrible change in the future is that extreme events may not occur singly, but several at the same time, which will cause special risks and make it more difficult for humans in most areas to respond. In addition, in the face of extreme weather events, not only humans cannot adapt quickly, but the ecosystem may not be able to adapt quickly. The large-scale death of coral reefs will eventually cause damage to the entire ecosystem.

Zhang Xuebin believes that every little bit of carbon emissions is beneficial to the planet. If mankind can reduce emissions quickly and on a large scale, it is still possible to avoid excessive global warming. Therefore, it is still very necessary for the international community to take immediate action.

4 Disaster prevention and mitigation must be prepared in advance, and scientific planning for resilient city construction will become a breakthrough

Responding to the global climate crisis by advancing carbon peak and carbon neutrality is a long-term process. Learning to deal with increasingly frequent extreme weather and reduce the damage it brings is also an urgent issue.

The current disaster prevention and mitigation early warning in my country mainly relies on various forecasts. Some experts believe that in addition to further detailing the content of local forecasts and warnings, it is also possible to implement disaster prevention and mitigation classification. Grading the possibility of disaster and the defensive measures that should be prepared, strengthen the defense mechanism of the central area of ​​the disaster, and arrange different defensive measures for the marginal area of ​​the forecast range according to the magnitude of the impact. For example, in the southeast coastal areas, reservoirs can be arranged for flood discharge before the typhoon comes, and in the northeast, inspections and investigations of urban drainage system failures need to be strengthened, and sandbags should be filled in low-lying areas. In addition, the establishment of a sound cross-regional and cross-departmental emergency coordination and linkage mechanism is also conducive to optimizing and integrating emergency resources, forming a joint force for disaster prevention and mitigation, thereby improving emergency response efficiency.

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After experiencing extremely heavy rainfall in many places recently, “resilient city” has also become a hot word of concern from all walks of life. The so-called resilient city refers to the city’s ability to withstand disasters, reduce disaster losses, and rationally allocate resources to quickly recover from disasters. The “14th Five-Year Plan” also specifically proposes to “enhance urban flood control and drainage capabilities, and build sponge cities and resilient cities.”

How to understand the resilience of cities? In the view of Zhao Yanjing, a dual-appointed professor at the School of Architecture and Civil Engineering and the School of Economics, Xiamen University, the city’s disaster prevention standards cannot be infinitely increased, nor can it be unaffected by extreme shocks. If the lifeline does not collapse, it can be carried over. Just like when a person is in shock, the breathing, blood, and heartbeat are still there, and they will wake up again.

In the face of floods, the core of maintaining the operation of the city is the power supply and backbone transportation. Without electricity, it means that high-rise buildings will be cut off, and the pumps of underground facilities will not work; the main road is flooded, and the rescue channel will be lost. Zhao Yanjing told reporters that in many cities, the water drains from the community to the road. In fact, it should be reversed. The water from the road flows to the community, and the water from the community flows to the green space and the water storage lake. “Extreme weather comes fast and walks fast. Sometimes it will be flooded for those two hours. Just keep the most important thing.” Zhao Yanjing said, the most important thing must be kept first, and plan in order of priority. This is the city’s resilience. reflect.

Zhao Yanjing has worked in China Urban Planning and Design Institute, Xiamen City Planning Bureau, China Eco-city Research Institute and other institutions, and has participated in the preparation and review of sponge city planning many times. He noticed that many of these plans, from design schemes to technical standards, are based on the experience of developed countries.

For example, whether a heavy rain falls evenly within 24 hours or pours down in a short period of time has completely different impacts on social operation and safety in production. Zhao Yanjing said that compared with most European and American countries, China’s precipitation is not particularly large but has short-term concentrated characteristics, which requires the planning of “sponge” standards based on actual national conditions.

With the increasing number of extreme weather affecting our country, a series of disaster prevention and mitigation measures have also been optimized and improved. “From the perspective of urban planning, disaster prevention must be weighed between cost and the value of the protected object.” Zhao Yanjing believes that the construction, maintenance and depreciation of infrastructure are all inputs, and many low-utilization facilities are built for extreme events. unrealistic. In fact, protection standards can only be improved with the improvement of the economic level.

In today’s cities, there are many underground concealed projects such as subways and tunnels, which not only have high daily maintenance costs, but are also very vulnerable to floods. Coastal cities like Xiamen usually have high groundwater levels, and the construction of an elevated bus rapid transit system (BRT) has little dependence on the outside world. Even after a typhoon, they have shown strong resilience.

Zhao Yanjing said that China has a vast territory, and the solutions of southern coastal cities may not be suitable for inland areas. The ancients built cities on the plains. In addition to defense, the city walls also played a role in flood control. “To sum up our existing successful experience, learn from ancient and modern Chinese and foreign disaster prevention wisdom, and create a set of disaster prevention plans that adapt to local characteristics.”

Our reporter Jiang Yongbin

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