Intelligently planned and protected urban green spaces are being introduced in 16 cities in the People's Republic of China to reduce flood risks and manage water resources.

Pingxiang, People's Republic of China - Flooding has become an all too familiar way of life for a large segment of Asia’s city dwellers. More than half of urban residents in Asia and the Pacific live in flood plains and low-lying coastal zones—including in such major cities as Bangkok, Dhaka, Guangzhou, Ho Chi Minh City, Kolkata, and Manila.

“Asia’s cities urgently need to reinvent themselves to become more resilient to the effects of climate change.”

Stefan Rau

Over recent years, severe and increasingly frequent floods have caused significant loss of life and damage. And in the face of climate change effects and rapid urbanization, the problem is poised to get worse. By 2050 about 64% of Asia’s population will be urban. In the People’s Republic of China (PRC) alone, there are at least 100 cities of more than 1 million residents. In India, 55% of the population is expected to be urban by 2050.

“Asia’s cities urgently need to reinvent themselves to become more resilient to the effects of climate change, flooding, and water scarcity,” says Stefan Rau, an Urban Development Specialist at the Asian Development Bank.

Historically, human settlements were founded near rivers and water was a lifeline and energy source for people, farming, and crafts. Settlers avoided floodplains and their settlements were fairly small with open space around them. Back then, there was, of course, no concrete and asphalt sealing off the soil from percolating rainwater.

Sponge city

In modern cities, cars and paved surfaces have become ubiquitous and engineered systems were built to manage storm water including drainage pipes under roads, large underground storage tanks, and deep tunnel systems in many cities. These systems are needed, but they are also costly and have limited capacity.

“By use of intelligently planned and protected urban green spaces, Asia’s cities can significantly reduce the risk of floods and manage water resources in a sustainable way, while also making cities more livable and green,” Rau says. “Picture a whole city that absorbs, harvests, stores, filters, purifies, and slowly releases rainwater—like a sponge. Rainwater is retained, naturally filtered and cleaned, and then slowly discharged into rivers and drained into the soil. This in short is the principle of the sponge city.”

In a sponge city, groundwater is recharged through a variety of green infrastructure such as preserved floodplains, storm-water wetlands, retention ponds, sunken parks, seepage wells, and green roofs.

An additional benefit, especially in water scarce regions and in light of increasing pollution and competing demands for water, is that such cities can harvest rainwater for farming and landscape irrigation. This contributes to water security, a key global and regional challenge given that Asia is the most water insecure region in the world.

“By utilizing multiple water related ecosystems services, a sponge city minimizes the impact of a city on the natural water cycle,” Rau adds.

Global experience

The idea of using green space to provide flood protection has been applied in many cities.

Berlin, for example, has large regional river and lake parks in the west and southeast, and a system of city parks and green riverbanks and canals. London has a system of regional green belts, large city parks and urban green squares. Chicago has an open space system with a regional lakefront park and a riverfront park system. It has also introduced a range of green infrastructure and guidelines for public and private development such as new parks, ample street trees, green roofs, green medians and planters, plazas, and parking spaces with permeable pavement and landscape areas.

Creating an Asian example

In Asia, meanwhile, the PRC is piloting the green infrastructure concept in 16 locations, with one of them a sponge city program backed by an ADB assisted project approved in 2014 for Pingxiang.

“Gray infrastructure for flood protection has been typical in the PRC, where we see solid walls and concrete dikes that force storm water into channels, potentially causing downstream flash floods and degrading river environments,” Rau says. “This approach harms river ecology, and prevents natural capacity to retain and filter rainwater runoff that flows into rivers.”

Pingxiang is a mountainous city with a population of nearly 2 million that has seen a rise in the frequency and severity of floods since 1998. Major floods between 1998 and 2014 affected more than 496,000 people, caused the collapse of more than 2,600 houses, and resulted in significant economic losses in agriculture. A flood that struck the city on 25 May 2014 caused an estimated $115 million in economic losses. Inadequate sewer systems and wastewater treatment have also severely affected water quality and the wider environment.

Assisted by the ADB loan of $150 million, the Jiangxi Pingxiang Integrated Rural-Urban Infrastructure Development Project will help protect floodplains, restore wetlands, and create wider green spaces along rivers. Through such initiatives, the project aims to address in a connected manner key challenges of flooding, river pollution, untreated wastewater, and lack of rural-urban linkages.

Embankments and wetlands along rivers will be rehabilitated and landscaped, helping to cleanse rainwater runoff. Rural embankments are planned as agriculture shelterbelts with edible crops and flood-resilient farming will include training for farmers in advanced organic crop growing.

“Public greenways along the rivers will create open spaces with enhanced water and rainwater management,” says Rau. “Given Asia’s urgent needs for flood remedies, hopefully the project will create a livable, green, and healthy city in Jiangxi that serves as a sponge city model for not only the PRC but the rest of Asia.”

Graham Dwyer is a Senior Communications Specialist in ADB’s Department of External Relations. Learn more about ADB’s work in the People's Republic of China and follow ADB’s Resident Mission in the country on Weibo.