How can the safety resilience of global mega cities be improved?, Extreme rainstorm occurs frequently
With the acceleration of climate change and urbanization, extreme weather disasters around the world pose serious challenges to urban safety and economic development, especially with the increasing frequency of extreme rainfall events, posing a threat to urban safety.
Super large cities with external energy supply not only have large population density, but also are more challenging in coping with extreme weather such as rainstorm due to their unique factor concentration and economic volume. Does climate change and human activities affect the natural environment? Why do extreme rainstorm occur frequently? How to enhance the resilience of cities and enhance their ability to resist and recover from major risk disasters? Li Yongkun, director of the Institute of Disaster Prevention and Mitigation of Beijing Institute of Water Science and Technology, recently received an exclusive interview with China News Service on "East West" to interpret the safety and resilience construction of super large cities against the background of frequent extreme rainstorm.
The summary of the interview transcript is as follows:
Li Yongkun from China News Agency: In recent years, global climate change has been severe. The sixth comprehensive assessment report "Climate Change 2023" released by the United Nations Intergovernmental Panel on Climate Change in March this year shows that global surface temperatures increased by 1.1 ℃ from pre industrial levels from 2011 to 2020. This not only causes more frequent and intense extreme weather events, but also poses increasingly serious threats to nature and humanity in every region of the world, posing serious challenges to human health and ecosystem health.
The impact of climate change on floods is particularly complex. On the one hand, the frequency and intensity of rainstorm change dramatically, directly changing the flood input conditions; On the other hand, the urbanization process changes the types of underlying surfaces such as vegetation and soil, exacerbates soil erosion, leads to an increase in peak flood flow, and results in the concurrent occurrence of mountain floods and debris flows, leading to a continuous increase in the risk of large-scale floods in watersheds.
In recent years, extreme weather events have occurred frequently worldwide, and natural disasters such as floods and droughts have shown a trend of increasing frequency, intensity, and breadth. In the northern region of China, the frequency and intensity of extreme heavy rainfall have significantly increased, exacerbating the risk of flood disasters in the semi humid and semi-arid regions of the north. The rapid transition of drought and flood, as well as the emphasis on both, have gradually become normalized.
At the same time, super large cities have high population density, high economic level, and large-scale development of underground space, resulting in limited flood control and storage space. The urban "rain island effect" and "heat island effect" are significant, and the characteristics of production and flow change dramatically. Extreme rainstorm events in super large cities generally have obvious local and sudden characteristics, including causing large-scale floods, mountain torrents and debris flows, waterlogging, etc., and have aggregation, chain and amplification effects, which not only threaten the safety of people's lives and property, but also may lead to the paralysis of communication, power, transportation and other lifelines, posing a great challenge to the safe operation of cities.
Li Yongkun from China News Agency: As a major gathering place for human habitation and economic wealth, once cities encounter extreme weather, they will generate a chain effect of risks, which may lead to huge losses of life and property.
In recent years, the dual pressures of climate change and urbanization have led to the frequent occurrence of extreme rainstorm events that broke the historical record worldwide. The main risks in the process of dealing with extreme rainstorm in super large cities include: first, extreme rainstorm causes highly disastrous floods, resulting in multi basin floods superimposed by external floods and regional floods, waterlogging, river floods, traffic paralysis, house damage and secondary disasters, such as mountain torrents and debris flows; Secondly, outdated and poorly designed drainage systems have limited the city's flood discharge capacity due to outdated drainage facilities; Thirdly, urban infrastructure is dense, and flooding events may seriously affect lifelines such as water, electricity, gas, communication, and transportation, increasing defense difficulties; Fourthly, urban expansion weakens natural control areas such as wetlands, water bodies, and green spaces, reduces flood buffering capacity, leads to a sharp increase in peak flow, and increases the risk of flood disasters.
London in the United Kingdom, New York in the United States, the capital circle of South Korea, Beijing in China, etc. have all experienced extreme rainstorm events, which are characterized by high short-term rainfall intensity and large cumulative rainfall.
Global mega cities have accumulated a lot of experience in dealing with extreme rainstorm and flood disasters. For example, countries such as the Netherlands, Germany, and Austria adopt multifunctional flood control projects and emphasize the establishment of a social disaster prevention system that coordinates government, society, and families. They actively use new technologies such as big data and digital twins to enhance comprehensive perception, accurate forecasting and early warning, operational scheduling, and emergency response capabilities. These measures aim to improve the city's ability to respond to extreme rainstorm and flood and other natural disasters, reduce the loss of people's lives and property caused by disasters, ensure the smooth operation of the city, and provide guarantee for future sustainable development.
Li Yongkun from China News Agency: The formation of extreme weather is a complex causal system with multiple interactive factors, and dealing with extreme weather is a complex system engineering. In urban planning and construction, combining the concept of "resilient cities", reserving space and outlets for floods, ensuring that the peak flood volume of main and tributaries matches, is crucial for preventing and responding to natural disasters, improving the sustainability and resilience of cities.
"Resilient city" refers to the ability of a city to maintain basic functions and quickly restore normal operations in the face of various pressures and impacts, including urban planning, infrastructure construction, emergency response mechanisms, post disaster assessment and recovery, and other aspects.
Nowadays, "resilient cities" have become a necessary option for the development and construction of many cities. So, how to build a "resilient city"? The hardware of a resilient city includes water conservancy infrastructure such as reservoirs, embankments, water gates, pumping stations, as well as regulation and storage spaces such as green spaces, lakes, and ponds. The strengthening of these hardware facilities can ensure proactive comprehensive defense before and during disasters, cut off the connection between disaster causing factors and disaster bearing bodies, and reduce the impact of disasters on the city. The software for "resilient cities" includes emergency plans, emergency response mechanisms, scheduling decision support systems, etc. These software measures can ensure that the city can quickly coordinate, respond, and rescue in emergency situations, minimizing losses.
Since the "7.21" extremely heavy rainstorm in 2012, Beijing has coordinated the construction of flood control projects and non engineering measures, carried out mountain flood and waterlogging disaster management and flood risk assessment and prevention, and the above measures have accelerated the prevention and control of urban flood disasters. However, facing extreme heavy rainfall events, urban defense capabilities still face significant challenges.
Since meteorological records began in 1951, there have been 12 weakened typhoons that have passed through or approached Beijing, bringing significant wind and rain impacts. At the end of July this year, the heavy rainfall caused by Typhoon Dussuri showed characteristics of long duration, large cumulative precipitation, strong short-term rainfall, and high overlap of rainfall areas. The total amount of rainfall in Beijing exceeded the total capacity of Guanting Reservoir. As the central area of rainstorm, Yongding River, Daqing River and Beiyunhe River basins are densely covered with mountain flood channels at the upper reaches, and the water flows rapidly down the mountain area. The flood volume is large and the peak value is high. The superposition of mountain flood and plain flood brings great challenges to the defense. The flood control engineering system composed of embankments, reservoirs, water gate hubs, and flood storage and detention areas plays a role in flood detention, storage, and peak shifting. Through effective scheduling, the benefits of flood control and drainage in the basin are realized. Beijing proposes to organically combine post disaster recovery and reconstruction work with resilient city construction, improvement of living environment, and implementation of rural revitalization strategy, and coordinate the promotion of recovery and reconstruction and regional development.
Faced with the test of extreme heavy rainfall events, the construction of super large cities needs to "adapt to nature, balance software and hardware", follow the overall idea of "watershed unit, spatial balance, and systematic governance", and use flood inundation lines as constraints to delineate flood channels and spaces, determine urban functional zoning, population size, and industrial layout, promote the construction of multifunctional flood storage and detention areas, strengthen social joint prevention and control, and support digital twins and other technological means to promote the transformation of flood control and disaster reduction to risk management. This requires the establishment of a sound monitoring and early warning system, early grasp of disaster situations, and dynamic and targeted release of early warning information; Resolutely respond to decision-making, with widespread public participation from all sectors of society; A scientific emergency plan shall be formulated to ensure the coordination and linkage between various departments to quickly respond to disaster disposal, so as to achieve the defense goal of "no major project breaking, no urban lifeline paralyzing, and no mass casualties" under extreme rainstorm and flood.
