Last month, in a stark example of the dangers of urban flooding, 59-year-old Mumbai doctor Deepak Amaraourkar was wading through knee-deep water to get home when he fell through a manhole cover and drowned. His body was found in a drain two days later.
During seasonal flooding at this time of year in Asia, such horror stories are far from unprecedented. In 2012, more than 70 people died in Beijing and nearly 50,000 were evacuated due to urban flooding. The scale of the devastation was unprecedented, and experts warn that massive urbanization coupled with poor planning and climate change are only going to make the problem worse.
How can densely populated cities, with overwhelmed drainage and depleted natural barriers, cope with this deadly inundation? China is pioneering one possible solution: “Sponge cities," in which systems are designed to absorb, clean and use rainfall in an ecologically friendly way that reduces dangerous and polluted runoff.
Soaks up water like a sponge
In cities, the sprawl of concrete infrastructures has vastly reduced the ability of water to be absorbed into the ground. The sponge city concept involves the building of infrastructure like green rooftops and permeable pavements, as well as reviving wetlands to store rainwater in the ground, which can also lead to groundwater recharge.
A man rides a bicycle through a flooded street after a heavy storm in Shanghai on July 30, 2009. Torrential rain and landslides have killed at least 66 people and left another 66 missing in south and central China since the beginning of June, state media reported on July 30. AFP PHOTO / PHILIPPE LOPEZ PHILIPPE LOPEZ / AFP
A man rides a bicycle through a flooded street after a heavy storm in Shanghai on July 30, 2009. Torrential rain and landslides have killed at least 66 people and left another 66 missing in south and central China since the beginning of June, state media reported on July 30. AFP PHOTO / PHILIPPE LOPEZ PHILIPPE LOPEZ / AFP
It was around two years after the capital’s floods that China first started really pushing sponge cities.
The Ministry of Housing and Urban-Rural Development has initiated pilot projects to turn 16 cities into sponges. The government is investing 897.4 million US Dollars from 2016 to 2018 in conserving rainwater.
The aim is for the 16 cities to conserve nearly 70 percent of all rainwater. As well as preventing flooding, the store can be diverted to agriculture and used for greening parks and cleaning roads.
Considering Chinese urbanization, the potential is obvious. According to the China Data Center, there are 11 Chinese cities with a population of more than two million, and nearly half of the country’s total 650 cities are prone to flooding.
Urban floods on the rise
As cities around the world have sprawled, drains designed for much smaller populations have proved inadequate. As a factsheet produced by Kingdom of Netherlands on China’s sponge cities says, “In Beijing, the construction of a drainage network didn’t match the pace of urban expansion that has witnessed a double expansion in the past 10 years.”
Beijing and Mumbai are, of course, not the only places affected by this issue. The world’s urban population hovered at around 14 percent in the 1900s, but today stands at nearly 54 percent, according to the United Nations. This figure is expected to grow to 66 percent by 2050.
Stefan Rau, urban development specialist with the Asian Development Bank, said climate change and massive urban development, among other factors, have contributed to increased impact of flooding in recent years due to environmental degradation and changes in the natural water system like the increase in paved areas, reduction of natural floodplains and wetlands that would normally retain and filter rainwater.
Rain chokes the drainage system that is already running at full capacity. “Rainwater runoff in cities comes from buildings, roads and other paved areas with little or no capacity of storm water retention. The quick accumulation of rainwater during the more frequent and more severe storm events over the past several years leads to urban flooding due to capacity limitations of many of the urban drainage systems,” Rau explained.
Data suggests that urban flooding has ravaged the majority of Asian cities. A study led by World Bank economist Stephane Hallegatte prepared a list of 20 cities that are most vulnerable to urban floods, and 13 of them are in Asia.
A study by the Population Reference Bureau shows that by 2025, seven cities from Asia are likely to be in the list of the top 10 most densely populated cities. With Tokyo, Bombay, Delhi and Dhaka occupying the top four spots and Calcutta, Shanghai and Karachi filling the bottom three.
A car lies on its side in the aftermath of floods at a residential area of Karachi on August 5, 2013. Pakistani disaster relief officials issued fresh flood warnings after the death toll from heavy monsoon rains rose to 45 and waters paralysed parts of the largest city Karachi. Flash floods caused by monsoon downpours have inundated some main roads in the sprawling port city and swept away homes in the northwestern province of Khyber Pakhtunkhwa. AFP PHOTO / RIZWAN TABASSUM
A car lies on its side in the aftermath of floods at a residential area of Karachi on August 5, 2013. Pakistani disaster relief officials issued fresh flood warnings after the death toll from heavy monsoon rains rose to 45 and waters paralysed parts of the largest city Karachi. Flash floods caused by monsoon downpours have inundated some main roads in the sprawling port city and swept away homes in the northwestern province of Khyber Pakhtunkhwa. AFP PHOTO / RIZWAN TABASSUM
Gray or green sponges?
Good sponge cities use a combination of "gray infrastructure" and “green infrastructure”. Green infrastructure uses the natural capacity of ecosystems to retain and filter storm water and makes cities resilient to climate change.
In urban areas where space is limited gray infrastructure is required, such as drainage pipes, underground tunnels and storage tanks to retain storm water like in Tokyo, Hong Kong, Chicago and many other cities.
“The challenge is to balance green and gray components of a sponge city and integrate their functions into an effective storm water management system. Good initiatives would include protecting floodplains upstream and within cities, restoring wetlands, creating green areas in the periphery of cities but also storm water retention parks and green channels inside dense cities to catch excess rainwater,” Rau said.
Sponge cities are not a new concept and similar ideas have been in use in many countries, including the US and Singapore. China has scaled up the concept, however, and many cities are learning from the pilot projects implemented there. Berlin has initiated massive afforestation in low-lying areas, and built permeable sidewalks and green rooftops to store rainwater.
PK Das, India based architect and winner of Jane Jacobs Medal - an award for individuals who create new ways of seeing and understanding cities - told CGTN that urban flooding cannot be controlled unless urban planners and governments act to protect natural resources in cities. “There should be a focus on building ecological cities that have its wetlands and aquifers that prevents floods,” he says.