Most Indian cities were built to get rid of rain as fast as possible. Concrete drains carry it off the street, and the system works until rain arrives faster than the pipe can take it. A sponge city reverses that logic. It holds rain where it falls, lets it soak into the ground, and releases it slowly. For flood-prone urban India, where drains are undersized and lakes have been built over, that reversal matters. It isn’t a cure. It is a far better starting point than another wider drain.
What Is a Sponge City?
A sponge city absorbs, stores, cleans, and slowly releases rainwater using permeable surfaces, green roofs, rain gardens, wetlands, restored lakes, and detention basins, working alongside conventional drains.
The idea is tied to Chinese landscape architect Kongjian Yu. After a 2012 Beijing flood that killed at least 77 people, China adopted sponge cities as a national strategy. A 2014 directive asked cities to recycle 70% of runoff in 20% of urban areas by 2020 and in 80% of them by 2030. Sixteen pilot cities followed in 2015, with 14 more added in 2016.
Why Do Indian Cities Flood?
Rainfall is only part of the answer. In many cities the stormwater system doesn’t match the density of new development, garbage and missing desilting clog the drains, and planners often lack a clear picture of topography and hydrology. Lakes and canals have been encroached on as well.
Bengaluru shows the result. In 2020 the BBMP identified 211 flood-prone areas in the city, 58 of them severely vulnerable. The problem isn’t limited to metros either. Belagavi and Dharwad have flooded too.
Tropical rain adds a second problem. It falls in short, heavy bursts, so a drainage design borrowed from a temperate country runs out of capacity quickly. This is why what happens in our climate-responsive architecture work matters at city scale as well as plot scale.
What Sponge Cities Look Like in India
Chennai is furthest ahead. The sponge park in Porur has three ponds that filter and store 845 cubic meters of water, overflow storage of 19,000 cubic meters, and a wetland with a total capacity of 30,000 cubic meters. It is designed for 25-year storm events. The Greater Chennai Corporation has built dozens of such parks, though reported counts range from 57 to 78 depending on the source and the date, so check the latest official figure before quoting one. Tamil Nadu set aside INR 880 million for sponge parks in Chennai, and a wetland sponge park opened there in March 2025.
Other cities are moving. Hyderabad is examining sponge neighborhoods in flood-prone areas, Kochi’s resilience roadmap includes decentralized sponge systems, and Gurugram is looking at sponge planning in its development rules. Andhra Pradesh has identified 64 water bodies across 15 cities for rejuvenation.
Much of this builds on older Indian practice. Tanks, stepwells, and lakes did the same job for centuries, and our pieces on blue-green infrastructure and stepwells show how.
What Else Do Sponge Cities Give Back?
Flood control gets the attention, but the side benefits often justify the spend. Water that soaks in recharges aquifers, which matters in cities that run short of water soon after the monsoon ends. Green and blue spaces also cool their surroundings. One report on Wuhan found that 389 sponge projects across 38.5 square kilometers reduced flooding, lowered temperatures by more than 3°C, and more than doubled land value.
A park that floods by design also gives the neighborhood somewhere to walk on dry days. Our note on green infrastructure in cities covers the design side.
Where Sponge Cities Fall Short
Zhengzhou is the case every planner should read. It was a designated sponge city, yet in July 2021 it received over 200 mm of rain in a single hour and more than 600 mm in three days, which overwhelmed its drainage. The city had spent more than $80 million since 2016 on green belts, permeable roads, and collection wells. Researchers note that China’s standards focus on annual rainfall volumes and don’t account for short peak events. A later State Council investigation found that only 32% of the money invested went to what the government defined as sponge city work.
Two lessons carry over to India. Sponge measures handle routine and moderate storms well. They do not handle a cloudburst, so drains, floodways, and early warning still need to exist. And soil matters. Designs have to be tailored to local terrain, rainfall, and soil, and clay-heavy Chennai is a different case from dense Bengaluru.
I would be wary of any city that presents sponge parks as its flood plan. Parks help. The heavy lifting still comes from restored lakes, working drains, and keeping buildings off natural flow paths.
What Architects and Developers Can Do at Plot Level
City programs move slowly. A single site can act now, and a few decisions make the difference:
- Read the drainage lines first. Find where water already flows across the plot and keep buildings off it.
- Cut paved area. Use permeable paving for parking and paths, and keep real soil for planting.
- Hold roof runoff. Storage tanks and recharge wells keep the first surge out of the street. See our guide to designing buildings that recharge groundwater.
- Treat the low point as a feature. A landscaped detention area handles a heavy shower and is dry the rest of the year. Green roofs take some of the load higher up.
Most new construction still ignores water, a gap we describe in why so little of what India builds plans for water. For the wider picture, read water-positive building design and resilient architecture.
Water-first thinking helps here. It means starting from where the water goes before deciding what to build, and we explain what it does and doesn’t mean in what water-first design actually means.
If you’re planning a project in a flood-prone zone, commission the soil test and a drainage survey before choosing any product. Ask your design team how the site behaves in a 25-year storm and a 100-year one. To see how we handle this, browse our case studies.
Frequently Asked Questions
What is a sponge city in simple words?
A sponge city is a city designed to soak up rain instead of draining it away. Parks, wetlands, permeable roads, and green roofs absorb and store water, which reduces flooding and recharges groundwater.
Why are sponge cities important for India?
Many Indian cities flood because drains are undersized, water bodies are encroached on, and surfaces are paved. Sponge features slow and stored runoff near its source, which lowers the load on drains during heavy rain.
Which Indian cities are building sponge cities?
Chennai has the most visible program, with dozens of sponge parks. Hyderabad, Kochi, Gurugram, and cities in Andhra Pradesh have announced sponge plans for water-body restoration.
Can sponge cities stop floods completely?
No. They reduce routine and moderate flooding but can be overwhelmed by extreme rain, as Zhengzhou showed in 2021. They work best with drains, restored lakes, and early warning.
What is a sponge park?
A sponge park is a public green space designed to capture, filter, and store stormwater. It typically uses ponds, bioswales, permeable paving, and recharge wells and doubles as a recreation space.
How is a sponge city different from rainwater harvesting?
Rainwater harvesting collects roof water for reuse or recharge. A sponge city is wider. It covers streets, parks, lakes, and drainage across a whole area, and harvesting is one part of it.