Sponge Cities Beating China’s Urban Heat
Urban flood prevention infrastructure has advantages in preventing urban heat.
Zhuhai, a city of 2.4 million people in the Guangdong-Hong Kong-Macau Greater Bay Area, is not what you might imagine as a city in the heart of the most populous region in the world. With 708 city parks, tree-lined waterfront promenades, and a connection between sea and mountain, Zhuhai is a tourist destination known as a forest city.
Zhuhai has not always been so leafy. In late 2014, China’s central government issued an edict promoting what it described as “sponge cities”. In 30 national pilot projects, with support of RMB 1.2 billion to 1.8 billion, China pushed urban design developed to prevent flooding.
According to Chinese guidelines, a sponge city is one that has transformed hard surfaces, such as roads and sidewalks, into permeable surfaces that can absorb, infiltrate, purify and store water, and then release the stored water for use. ‘use. In other parts of the world, similar infrastructure projects are known as low impact development, blue-green infrastructure or water-sensitive urban design. But only China has implemented them on a city-wide scale.
Zhuhai has built more than 115 square kilometers of urban sponge infrastructure since 2016, accounting for nearly a quarter of the total urban built-up area. Zhuhai has brick or porous concrete pavements, porous asphalt roads, green roofs, green shoulders, bioretention ponds, ponds, rainwater wetlands, grass swales and buffer zones of vegetation.
Zhuhai’s urban flood prevention measures also help fight urban heat
The “sponge cities” have succeeded in alleviating the problems of urban flooding. But they also have the unintended benefit of reducing deaths from urban heat. This is important because extreme heat kills.
Across Europe, extreme heat events in 2020 are estimated to have caused a total of 6,340 additional deaths in France, Belgium, the Netherlands and the UK. Meanwhile, in British Columbia, Canada, the summer 2021 heatwave caused 569 additional deaths in a matter of weeks. Cities are often the most dangerous place during a heat wave, with studies showing they can be up to 10-12°C warmer than surrounding rural areas.
Although urban heat has been identified as a silent killer and one of the deadliest weather disasters, formal responses have not been well implemented. In China, there are no plans, policies and actions dedicated to the mitigation and adaptation to urban heat. Potential district cooling strategies are also hampered by the changing built environment and urban sprawl, especially in developing countries. But controlling urban flooding through urban sponge systems can have huge benefits for urban heat mitigation.
For example, a study in Guangzhou, China, suggested that adopting porous bricks and porous concrete could lower pavement surface temperatures by 12 and 20 degrees Celsius, respectively. The air temperature can be reduced by up to 1 degree Celsius.
A green roof – covered with vegetation – reduces rainfall runoff, mitigates flooding, and can reduce ambient temperature and alleviate heat stress through evaporative cooling in the summer. A case study in Hangzhou, China, indicated that green roofs could generate moderate effects in reducing pedestrian air temperature (about 0.10 to 0.30°C), while achieving a maximum cooling performance of 0.82°C.
A sponge city can achieve synergies of urban flooding and urban heat island mitigation, and the co-benefits could be applied in countries that already have low-impact water management practices in place.
In China, the co-benefits approach is already working: investments in sponge cities at the national and provincial levels can be used to subsidize urban heat mitigation works.
In addition to reducing temperature and flooding, a sponge city can provide financial, institutional, and social benefits.
Building a sponge city is able to connect different government departments and improve synergies, but only if there is a clear division of responsibilities. Industry and the private sector can also play an important role in providing social and financial support. Policies that detail everyone’s role are needed, as well as a technical database that includes solutions to likely problems across all disciplines and evaluates the performance of common techniques.
Sponge city works can also improve social equity by reducing ambient temperature, improving outdoor thermal comfort, reducing heat-induced morbidity and mortality, and alleviating energy poverty.
Other urban heat mitigation projects can be achieved through a sponge city approach, such as green buildings, low-carbon eco-cities, smart cities, forest cities, and heat treatment. mist. Many challenges from a technical, economic, social and institutional point of view remain, and local pilot projects are necessary for the evaluation of performance, the optimization of projects and the reduction of uncertainties and risks.
Beyond the mountain-sea-city landscape, Zhuhai is experiencing rapid economic development and a thriving arts and culture scene. Green-blue infrastructure development has not been a hindrance to the city’s continued growth. This world-class example shows the multiple benefits achieved through sponge cities – a glimpse of a future that seems safer and fairer for everyone.