Absorbing the Chinese way to prevent floods 

Bangkok followed Malaysian cities in being submerged by flash floods this week. Scenes of people, cars and buildings sunk deep in murky water are becoming almost an everyday phenomena, as cities across Southeast Asia are paralysed in the grip of climate change. The time has now come to get past the shock and complaints and find the solutions. 
China is doing just that, turning 30 of its flood-prone areas into “sponge cities” to prevent flooding and to retain rainwater.
The Chinese plan is big and fast. It launched the sponge city project in 2015, but it aims to retain 70 per cent of rain in 80 per cent of urban areas by 2020. The sponge concept is set to spread rapidly as part of global efforts to reduce the impact of increased rainfall and floods amid rapid climate change.
The concept figures prominently in the plans of Penang, where state executive Chow Kon Yeow contrasts the situation now when rain falls with what used to happen. 
In the past, 50 per cent of the rain was absorbed by natural ground cover (trees, grass, etc) and into the ground. There was 10 per cent water runoff (to rivers and drains) and 40 per cent evaporation back to the atmosphere).
The trees, green spaces and their soil acted as a sponge to absorb the rainwater, preventing it from building up into flash floods.
With urbanisation, the green spaces have now been paved with cement and concrete. Now, only 15 per cent of the rain infiltrates the soil, while the runoff has increased to 55 per cent and evaporation is 30 per cent. Penang’s “sponge” now absorbs just 15 per cent of the rainwater compared to 50 per cent previously.
Scientist Dr Kam Suan Pheng quotes former Penang Water Authority general manager Kam U-Tee as saying that the October 2008 Penang floods were caused by conversion of the valleys into “concrete aprons that do not retain water”. As a result, the water immediately formed streams, causing flash floods, even with moderate rainfall.
Given this analysis, a key part of tackling the floods is to reverse the loss of the natural sponge. In recent decades, Malaysia and its neighbours have seen the conversion of a lot of farms, parks, trees and grass areas into concrete jungles of roads, houses, commercial buildings and car parks.
There now has to be high sensitivity to the valuable environmental and economic roles of trees, gardens, fields and grasslands, and parks. The aim of garden cities is not just to be pleasing to the eye but to be a very important part of development as well.
Now comes the role of sponge cities. The world is applauding the Chinese initiative to counter floods and improve water security by building up the natural “sponge” cover in its cities.
In 2010, landslides caused by flooding killed 700 people in China. 
Five years later China launched the Sponge City initiative, which now covers 30 cities, including Shanghai, Xiamen and Wuhan. The target: by 2020, 80 per cent of its urban areas will absorb and reuse 70 per cent of rainwater.
The many types of projects include:
 – Constructing permeable roads that enable water to infiltrate the ground.
 – Replacing pavements on roads and parks to make them permeable.
– Building wetlands to absorb and store rainwater.
 – Constructing rooftop gardens (for example, 4.3 million square feet in Shanghai).
– Planting trees on streets and public squares.
– Building community gardens and parks to expand green spaces.
– Building reservoirs and preserving agricultural land to hold water.
“In the natural environment, most precipitation infiltrates the ground or is received by surface water, but this is disrupted when there are large-scale hard pavements,” said Wen Mei Dubbelaar, water management director at China Arcadis, echoing Dr Kam’s point.
“Now only about 20-30 per cent of rainwater infiltrates the ground in urban areas, so it breaks the natural water circulation and causes water logging and surface water pollution,” Wen told the Guardian.
In Shanghai’s Lingang district, the streets are built with permeable pavements. There are rain gardens filled with soil and plants, buildings feature green rooftops and water tanks, and a manmade lake controls water flows, reports the Guardian.
Prof Hui Li at Tongji University said the first priority is to preserve or restore natural waterways – the natural way to reduce flooding risk.
In Wuhan, many of the city’s small rivers were filled in during building. But Lingang still has agriculture land and a lake to hold more water during heavy rain.
What about the cost factor? So far the Chinese cities have received over US$12 billion (Bt376 billion) for sponge projects. The central government is funding 15-20 per cent of costs, with the rest coming from local governments and private developers.
But compare this to the US$100 billion of direct economic damage due to floods in China between 2011 and 2014, plus the human lives lost.
Sponge cities are the way to go for the future. Our own governments – federal, state and municipal – should study this option seriously, as the public braces for more floods ahead.