When the rains arrive, a city can change within hours. Roads turn into rivers, underpasses disappear under water, and overflowing drains bring traffic to a standstill. Yet, just months later, many of these same cities can be worrying about falling groundwater levels and water shortages.
This is the strange water paradox facing growing cities: too much water in one season, and too little in another.
Part of the problem is what lies beneath our feet. As cities expand, natural surfaces such as soil, wetlands, ponds and open spaces are replaced by concrete, asphalt and buildings. Rain that would once have slowly seeped into the ground now hits these hard surfaces and rushes into drains.
In India, the built-up area across the country’s 10 most populous cities grew by 52% between 2000 and 2015, according to a World Resources Institute study cited by the Good Food Movement. Much of this expansion happened over areas important for groundwater recharge.
So, what if cities were designed to absorb rain instead of simply trying to drain it away?
Think of a city like a sponge
Instead of treating every drop of rain as something that needs to disappear through a drain as quickly as possible, sponge-city planning gives water places to pause, seep into the ground, collect and slowly move away.
Sponge cities slow, store and absorb rainwater, giving it time to seep into the ground instead of rushing into drains. Photograph: (Well Labs)
This can mean restoring lakes and wetlands, creating rain gardens, planting trees and vegetation, using permeable pavements that allow water to pass through, or even designing parks and playgrounds that can temporarily hold excess rain.
The science is actually quite simple: slow the water down.
Think about pouring water onto a tile versus a patch of soil. On a tile, water stays on the surface and runs towards a drain. Soil, on the other hand, can absorb some of that water.
Permeable pavements take this principle into an urban setting. Unlike conventional concrete or asphalt, they contain interconnected gaps that allow rainwater to pass through the surface into layers of gravel and soil underneath. Some water can be stored temporarily in these layers, while some slowly infiltrates the ground.
Rain gardens work in a similar way. Runoff from a nearby road or roof can be directed into a shallow planted area, where vegetation and soil slow the water, filter some pollutants and allow part of it to soak into the ground.
Wetlands and ponds work slightly differently. They act as temporary storage spaces, holding excess water instead of allowing a large volume to rush into drains and rivers at once.
What are ‘sponge streets’?
You don’t need to redesign an entire city to make it more “spongy”.
Take a regular street. Its edges can be designed with bioswales — shallow, planted channels that collect and slow down runoff. Footpaths and parking areas can use permeable surfaces, while rain gardens can collect water from nearby roads and buildings.
Instead of rushing rain into drains, sponge-city design gives it time to collect, filter and seep into the ground. Photograph: (McD Berl)
Trees and vegetation can also intercept rainfall and help the soil retain water.
Each intervention may seem small, but together they create a network of spaces that can capture, slow, store and absorb rainwater, reducing the sudden load on urban drainage systems.
The idea came from China, but the principle isn’t new
The term ‘sponge city’ is closely associated with Chinese landscape architect and urban planner Kongjian Yu, who developed the concept in the early 2000s. The approach was later incorporated into China’s national urban policy in 2014.
Cities may never stop flooding completely, but giving rain more places to go can make them better prepared for the next downpour. Photograph: (Well Labs)
Yu’s thinking was influenced by natural landscapes and traditional water systems. Rather than relying entirely on concrete drains and channels to move water away, his approach asks cities to work with the landscape — giving water room to spread, settle and soak into the ground.
The principle itself, however, is hardly new to India. Traditional systems such as johads, ponds and stepwells have long been used to capture, store and manage rainwater.
Can this actually help Indian cities?
India is already experimenting with several elements of the sponge-city approach.
In Chennai, a degraded wetland in Porur was restored as the Dr M S Swaminathan Wetland Eco Park. Its network of ponds and wetland plants is designed to hold and filter stormwater before releasing it downstream.
According to reports, since its opening in 2025, the park has managed more than 20 million litres of stormwater during peak monsoon periods and can handle over 90% of runoff generated on-site.
Ahmedabad, too, has experimented with sponge-park designs using permeable paving and underground systems to help rainwater move below the surface rather than immediately becoming runoff.
And in 2024, the government approved nearly $300 million across seven major cities, including Mumbai, Chennai and Bengaluru, for urban flood management and water conservation. The programme includes expanding water bodies alongside conventional drainage and early-warning systems — reflecting a broader move towards combining natural systems with traditional infrastructure.
But there is an important caveat: a sponge city is not a city that can never flood.
From bioswales and rain gardens to permeable pavements, small changes can turn ordinary streets into spaces that capture and manage rain. Photograph: (CNN)
No park, wetland or permeable road can absorb unlimited amounts of rain, particularly during an extreme cloudburst. These systems also need to be designed around local soil, topography, groundwater conditions and existing drainage networks.
The real strength lies in combining the old and the new — drains and wetlands, pumping stations and parks, concrete infrastructure and natural systems, so that a city has more than one way to deal with the next downpour.
For India, that may be the most useful lesson from the sponge-city idea: we don’t necessarily need to make our cities entirely ‘spongy’. We need to give water more places to go before it overwhelms the drains.
