Zhengzhou floods serve China's urban planners deadly warning

by Reuters
Friday, 23 July 2021 09:03 GMT

A man stands on a stranded vehicle on a flooded road following heavy rainfall in Zhengzhou, Henan province, China July 22, 2021. REUTERS/Aly Song

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Official data shows about 98% of China's 654 major cities are vulnerable to flooding and waterlogging

By David Stanway

SHANGHAI, July 23 (Reuters) - The catastrophic floods that struck the central city of Zhengzhou during the past week have given China's urban planners a foretaste of future disasters as climate experts reckon the country had better learn to live with record-breaking rainfall.

Official data shows about 98% of China's 654 major cities are vulnerable to flooding and waterlogging, with rapid growth in recent decades creating urban sprawls that covered floodplains with impermeable concrete.

At least 51 people were killed in Zhengzhou, many of them drowning in a subway system as the deluge on July 20 dumped 800-900 millimetres of rainfall in what was described by Chinese media as a "once in a thousand year" event.

"We can't verify whether this is 'once in a thousand years', said Zhou Jinfeng, Secretary-General of the China Biodiversity Conservation and Green Development Foundation (CBCGDF), a non-government group.

"But because of global climate change, the rainfall statistics will continue to break new records in the future."

Almost two-thirds of China's 1.4 billion people live in cities compared with a third two decades ago, and coping with future calamities will depend on building infrastructure, most notably flood prevention and drainage systems, experts say.

Currently, many cities rely on the height and strength of dykes as a first line of defence.

"We know these big events are going to come along, and just don't know when," James Griffiths, a hydrologist at New Zealand's National Institute of Water and Atmospheric Research, said.

"City planners need to consider the hydrology of the larger landscape - floodplains and natural basins - when they design new cities, and ensure that the drainage network can continue to utilise such areas when the big rains arrive."

China published a policy report this month listing some of the measures taken to mitigate risks. More than 6,700 reservoirs were reinforced and there were plans for drainage infrastructure at 53 flood-prone sites along the Yangtze, the country's biggest river.

SPONGE CITIES

Located just south of the Yellow river, Zhengzhou is one of hundreds of cities that need to be retrofitted with flood-proof infrastructure.

In Zhengzhou in the last few days, China has relied on the giant South-North Water Diversion Project to try to ease flood pressures.

It frequently uses giant dams along flood-prone rivers like the Yangtze and the Yellow to try to regulate water flows and minimise flood peaks.

But China has also been looking for more natural, low-impact solutions to solve its growing flood vulnerability.

China launched a programme in 2015 to create "sponge cities" that could safely retain and drain more rainwater.

The first phase covered 30 cities across the country, including Hebi, 150 kilometres (93 miles) from Zhengzhou.

Among the potential technological solutions were permeable asphalt and pavements, and cities were also encouraged to expand green spaces, build ponds and restore wetlands to take on surplus water.

Faith Chan, associate professor with the School of Geographical Sciences at the University of Nottingham Ningbo, said "sponge city" measures are designed to cope with around 180-200 millimetres of rain over 24 hours, and would have been powerless against the downpour of biblical proportions that swamped Zhengzhou.

Zhou of CBCGDF said in a blog post that practical measures such as waterproofing subway systems needed to be backed up by fundamental changes in how cities are designed, noting that the challenges will get harder in the coming years.

"We hope this will serve as an important warning and ring an alarm bell for our industries and government departments to take action quickly, to change quickly, and prevent this kind of disaster from happening again." (Reporting by David Stanway; Editing by Simon Cameron-Moore)

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