 "Can ‘sponge cities’ be the solution to floods as seen in Dubai?")
Countries across the world are struggling in the face of climate change.
From China to the UAE, the problem of flooding keeps rearing its ugly ahead again and again.
But now some are turning to a novel solution – ‘sponge cities.’
But what are they? How do they work? And will they change the way we handle rain?
Let’s take a closer look:
What are they?
EuroNews.com defines sponge cities as a ’nature-based solution.'
These cities make use of their terrain to keep water at its source, slow its flow down, clean and reuse it.
This is accomplished by waterproofing the paved floor so part of the water evaporates and the rest is slowly drained.
According to Business Standard, these cities work by having surfaces that mimic sponges that absorb water.
This is then filtered via the ground soil and sent to urban aquifers.
The water can be drained through urban or peri-urban wells, treated, and used for the city’s water supply.
Such cities are
Environmentally adaptive
Systematic and comprehensive
Environmentally friendly
The idea behind these cities is to keep water in urban areas and tackle shortages. This can also be aided by planting more trees and constructing smart buildings.
This includes covering roofs in grass to better absorb water and painting buildings in light colours to refract the heat rather than trapping it, as per EuroNews.
Impact Shorts
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As per Business Standard, another aim behind sponge cities is to aid ecology and biodiversity.
The concept was first formulated in China in the early 2000s.
Beijing did so with an eye on tackling surface-level flooding in urban areas.
In 2014, China began experimenting with pilot projects across the nation.
Each city had a budget of around 400 to 600 million yuan, as per the newspaper.
EuroNews credits professor Kongjian Yu as the brains behind the concept.
Yu, an ecological urban planner and landscape architect, teaches landscape architecture at Peking University.
He is also founder of the planning and design office Turenscape in Beijing.
Yu was inspired by integrated urban water management (IUWM) strategies including sustainable drainage systems (SuDS) in the UK and low-impact developments (LID) in the US.
These concepts are being put into practice.
According to The Guardian, Amsterdam has covered 45,000 square metres with ‘blue-green’ roofs.
These absorb rainwater that can be used by residents of building to water plants and flush toilets.
As per Wired, Los Angeles has been making use of ‘green spaces’ on roadsides and along medians for years.
The city, perennially plagued by water troubles, had to change its thinking.
“Before, the city would see stormwater as a liability,” Art Castro, manager of watershed management at the Los Angeles Department of Water and Power told the outlet. “It would be a hindrance, it would be a flooding issue, it would create erosion. So, 11, 12 years ago, we kind of had a paradigm shift, and we started looking more at it as an asset.”
The city now has green spaces on the street that send water to underground tanks.
The Los Angeles Department of Water and Power estimates it will take in 16,000 acre-feet (water that would go a foot deep across an acre of land) of rainwater per year.
This is enough to fulfill the needs of 64,000 homes.
For Yu, this is a deeply personal battle.
Yu, speaking to NPR, recalled how nature literally saved his life during a flood.
“…I survived. You know why? Because I grabbed the willows, weeds, the reeds, along the riverbank,” he added.
What do experts say?
Experts say they are vital in today’s times.
“Though grey infrastructure of concrete, steel, pipes and pumps, can be necessary to solve urgent individual problems, it consumes huge amounts of concrete and energy, lacks resilience and often accumulates a higher risk of disaster. It breaks the connection between man and nature,” Yu told Euronews.
“More than ever, facing global climate change and destructive industrial technologies, we have to rethink the way we build our cities, the way we treat water and nature, and even the way we define civilisation.
“Sponge Cities are inspired by the ancient wisdom of farming and water management that use simple tools to transform the global surface at a vast scale in a sustainable way.”
As Michael Kiparsky, director of the Wheeler Water Institute at the University of California, Berkeley, explained to Wired.com, “Where once there were forests and fields and wetlands that would soak up the rain, these have been paved over and replaced with surfaces that do not absorb rain.”
Surfaces such as concrete sidewalks and asphalt roads.
“The denser cities are developed, the more impervious surfaces are used, the worse the impacts of climate change are becoming,” Kiparsky added.
“Once the capacity of these structures is exceeded, then water starts backing up, and its problems are exacerbated because of the lack of the natural absorbency of large areas of soil and vegetation.”
It has other benefits too.
“Natural infrastructure like vegetated swales can not only slow down the hydrology—that is, reduce the speed with which this runoff accumulates in these natural systems—it can also actively clean the water,” Kiparsky said.
“The most interesting part about natural infrastructure that’s used to create sponge cities is the fact that it is a multi-benefit approach,” says Kiparsky. “It does many, many things—and it does many things that traditional infrastructure simply can’t do.”
“We think the concept is applicable to many urban areas around the world,” Kasper Spaan, policy developer for climate adaptation at Waternet, Amsterdam’s public water management organisation, told The Guardian. “In the south of Europe – Italy and Spain – where there are really drought-stressed areas, there’s new attention for rainwater catchment.”
Up to 50% more cost effective
Business Standard quoted a World Economic Forum (WEF) as showing that ’nature-based solutions to climate change’ were up to 50 per cent more cost-effective than engineered alternatives.
The report on sponge cities in China said it also added 28 per cent value compared to just infrastructure.
Shanghai, New York, and Cardiff have all taken steps to ‘become spongier,’, according to the United Nations Framework Convention on Climate Change (UNFCC).
The outlet quoted a 2022 study by multinational firm Arup as showing that Mumbai ranked third out of seven major cities when it comes to ‘sponginess’.
Mumbai, which netted a 30 per cent rating, was tied with New York and Singapore.
But critics point to recent floods in China as showing the limitations of sponge cities.
Zhengzhou in China’s Henan province, went all in on the sponge city concept.
Despite granting the programme around 60 billion yuan to the programme from 2016 to 2021, it could not handle the 2021 downpour.
Some experts estimate that sponge cities cannot cope with more than 200 millimetres of daily rain.
In August 2023, one station in Beijing recorded 745 millimetres in three and a half days.
Zhengzhou itself witnessed rainfall that exceeded 200 millimetres in just one hour.
The country has a huge problem with climate change.
According to 2018 data, 641 out of 654 large- and medium-sized cities in China are vulnerable to flooding and waterlogging, with 180 facing flood risks every year.
‘Misunderstanding of scale’
Others dispute the notion that sponge cities don’t work.
Erica Gies, author of a book about water management called Water Always Wins, told NPR, “People see a city in China flood from a heavy rain and then they say sponge cities doesn’t work, but that’s a fundamental misunderstanding of scale.”
“It’s a growing movement. But it needs to grow a lot faster and at much bigger scale for it to really help reverse the really extreme scale at which we have altered the natural water cycle” she added
“If you have a sponge city project in five square miles of a city but your city covers hundreds of square miles, it’s not surprising that that wouldn’t be sufficient to prevent the flooding,” Gies explained.
Yu, meanwhile, said the problem is with people’s mindset.
“We still trust that concrete can solve the problem. We still trust that technology can solve the problem,” he told the outlet.
With inputs from agencies
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