Transforming Urban Areas into Sustainable 'Sponge Cities' Offers Global Benefits

Compact, low-carbon cities are pedestrian and bicycle-friendly. Photo: ADB
Compact, low-carbon cities are pedestrian and bicycle-friendly. Photo: ADB

By Stefan Rau

Sustainable urban development and urban design is central to climate change action. As the People’s Republic of China shows, Integrated compact sponge cities are pivotal for low-carbon development and for building climate resilience.

Most of the planet’s eight billion people live in cities, where most economic output is generated, where people on average earn higher incomes, and also where most greenhouse gases are emitted and most waste is generated. Urban areas are also most affected by climate change impacts. 

There is a direct link between the density of a city and the use of private vehicles. Studies show that in urban regions with low density, sprawling into suburban and peri-urban areas people drive around with their cars a lot and this generates traffic that emits a lot of carbon emissions. 

In cities with higher density people walk and cycle more and use more public transport and emit less greenhouse gas emissions. This example demonstrates that sustainable cities are a global public good. And the flipside is that unsustainable cities are a public bad. 

Therefore, cities and how they are planned, built and used every day by residents are central for climate change action. Let’s support urban residents who choose low-carbon and resource-efficient lifestyle choices and that they are safe from climate change hazards. What can we do for example in the People’s Republic of China?

About 66% of people in the People’s Republic of China live in cities and urban areas. The country has made remarkable progress especially since the 1978 opening up and reform policy was launched. The standard of living for millions of people was raised significantly. And the country strategically linked and mutually enabled and simultaneously unleashed urban and economic development. But major challenges remain. 

Urban development in the People’s Republic of China has been based on a supply-side model with massive expansion into the outskirts. As a result, there is a significant oversupply of industrial land and infrastructure, residential land and apartments, and commercial space. This is true for the country as a whole, while there is a regional mismatch of supply and demand, with generally more supply in lesser cities and territories.

Compact, low-carbon cities and sponge city models are strategic principles that not only provide climate resilience but also enhance urban livability and sustainability.

Urban growth has been slowing down and the People’s Republic of China’s society is transforming. People are ageing and the population is on a very rapidly declining trajectory.  Many cities and urban areas already experience population decline – which requires urban planning and management.

The urban model in the People’s Republic of China is carbon-intensive: it is expanding horizontally, it is based on land-use separation generating traffic for people to travel from home to work, to learn, to shop and to recreate.

It is based on large urban superblocks and wide roads which makes urban areas very inconvenient for walking and cycling – even generates unnecessary traffic and traffic jams.

The institutional responsibilities are well defined and distributed among various line agencies on national, provincial and local levels. Existing planning and engineering codes are well defined and research and design institutes and the construction industry are all well accustomed to the supply-side carbon-intensive model.

There is a challenge of departmentalization (silos) and there is need for more effective cross-sector cooperation. There is a significant system inertia. It is challenging to steer the ship into a new direction. Institutional strengthening and effective interagency coordination mechanisms are needed. 

A compact sponge city will be a low-carbon climate-resilient city. In a compact sponge city people are safer from flood and urban heat risk.

Looking to the future, how can we transform and retrofit urban areas in the People’s Republic of China towards more sustainable urban models? There are many valid strategies and solutions being discussed, and let’s focus on compact cities and sponge cities.

Compact, low-carbon cities.  A compact city follows transit-oriented development principles and is dense, has a vibrant mix of uses, is efficiently and well served by public transport and other urban infrastructure and services. It is pedestrian and bicycle-friendly, it is safe and attractive, it is green with public parks and street trees. 

You can live near where you work. You can shop near where you live. You can go to school and to hospital near where you live or get there conveniently and safely with public transport and on bicycle. You choose to walk and cycle for convenience and efficiency. Doing this you emit less carbon as a result.

Compact cities are the most strategic principle for a low-carbon urban area as it determines urban form, it needs less energy for transport, less energy for heating and cooling, if well-designed on all levels, and it provides benefits from good economic productivity. The compactness needs to be integrated with concepts for resilience, resource efficiency, health, livability as integration is a fundamental principle of a sustainable, inclusive and competitive city.

Sponge city with nature-based solutions is a resilient city. Sponge city applies nature-based solutions to build climate-resilience. When we build a city we pave over former green land constructing roads, buildings, yards, plazas, and parking spaces. Rainwater cannot seep into the ground but runs off on the hard surface. 

We need to build drainage systems, like gutters, drainage pipes, ditches and canals that will collect urban runoff and discharge eventually into the river or the ocean (hopefully treated). With the changing climate rainstorms occur more frequently and they dump more rainwater in shorter time. 

 A sponge city re-introduces green spaces with the function to capture and retain stormwater, infiltrate into the ground and/or harness rainwater for later reuse and slowly release into the rivers. This reduces the water masses to be handled by drainage systems that drop on an urban area in very short period of time during heavy storms, which are expected to increase every year. 

Sponge cities are resilient and with climate mitigation co-benefits. That makes sponge cities also a global public good, beyond just local and regional benefits from resilience.

A compact sponge city will be a low-carbon climate-resilient city.  In a compact sponge city people are safer from flood and urban heat risk. They choose to walk because it is beautiful and green and safe and convenient. They enjoy meeting each other on sidewalks, on plazas and in parks. They make it a habit to walk and cycle, play and do sports in parks, walk and run along a river greenway, watch the butterflies, listen to the birds and enjoy a kayak ride. Such a city is therefore also healthier and more age-friendly and contributes to urban biodiversity if designed well. 

More people would choose not to migrate away from such a safe city and there will be less of a need to build infrastructure and buildings in another place for potential climate migrants.

Such urban planning and urban design, integrating nature-based solutions and compact city principles, will contribute as global public goods in the People’s Republic of China and around the world.