Sponge city concept is neither uniquely Chinese nor new in India, given the Indian way of life where communities learnt to live with water

When it did not stop raining even on the eve of Navratri in Mumbai, well into the third week of September, worry was writ large for many in the city. When it poured incessantly and voluminously to flood Kolkata on Mahalaya and after, the city struggled to stay afloat. Virtually every major and other city has seen intense rain, flash floods, cloudbursts and so on this season, bringing in untold devastation, adverse health and economic impacts, and misery to millions. Nearly every country has had unprecedented urban floods this year.

Mumbai, like other cities, has been grappling with flood management plans, climate action plans, and suchlike for about a decade now. The thrust of these, however, has been on engineering and technological solutions to combat floods or drain the rain faster or prevent waterlogging. Water pumps are now de rigueur across the city. The municipal authorities say this approach is working because even if there’s waterlogging from heavy rainfall, it drains out faster than it used to.

Kolkata has seen less of such solutions. Locals say it took hours and days for the rainwater from, say, Dhakuria to ebb away completely. Delhi’s flooding spots are, of course, legendary. So are Pune’s and Bengaluru’s. Every city, really. This is not only about rainfall patterns shifting in the era of climate change—more intense rainfall over shorter durations has become the norm. Cities are facing the fallout of the unsustainable building model promoted from the West and embraced across the world.

In this model, the natural ecology of the city does not matter—hills are flattened out, forests are hacked, thousands of trees are axed if they are in the way of massive construction projects, water bodies are landfilled without a second thought, river floodplains are claimed as developable land and built upon, lakes are turned into sites of construction, and coastlines and marshlands are not respected. All in the name of ‘development’. There has to be another way to build cities—or rebuild them.

One of them, from China, is the concept of ‘sponge cities’. Among the world’s well-known landscape architects, Kongjian Yu has been credited with conceptualising and popularising the sponge city model since the 2010s, with the Chinese government buying into it and investing heavily. As many as 20 cities were selected for pilot projects in 2015-16, and a systematic nationwide rollout began in 2021, which now encompasses 60 “model cities” with investments running into millions of renminbi. The record-breaking flood in Zhengzhou in 2021 fuelled criticism against the sponge city approach, given that the municipality had invested the equivalent of over USD 80 million to make it a sponge city, but Yu defended that it could not be called a sponge city, given the overwhelming presence of grey infrastructure in it.

The sponge city approach or model is seemingly simple—treat the city surfaces as natural sponges that can absorb, store and reuse the maximum amount of rainwater so that the flood risks are minimised. 

It relies upon nature-based solutions, such as creating green roofs and inner-city gardens, remaking pavements and spaces with permeable surfaces for water to seep in, improving river drainage, and clearing wetlands to hold the rainwater or slow down the runoff that causes waterlogging. The Western media and climate circles, not surprisingly, questioned Yu’s approach—along with that of his firm Turenscape, which works in many Chinese cities—and the Chinese government’s wisdom in sinking large sums of money into making sponge cities.

It did not help that Yu was Harvard educated. Expect this debate to resurface in the event of Yu’s tragic death on September 24 in an air crash in Brazil. He was there to participate in a conference and was filming with a crew in Pantanal, the world’s largest tropical wetland, when their small aircraft crashed. But Yu’s words and philosophy will outlive him. “It’s important to make friends with water,” he once remarked and added on the sidelines of the Brazil conference that “cities must retain water, slow down water, and embrace water.”

In a sense, the sponge cities concept is not only about remaking cities to absorb, store and reuse rainwater; it asks cities to rethink their relationship with water itself, which is limited to a purely utilitarian one with usable water often brought from rural areas many kilometres away or bracing and building against urban floods. Even coastal cities like Mumbai, Kolkata, and Chennai have a skewed relationship with their water bodies and water—and, by extension, rainfall. “Making friends with water” and embracing it might be a way forward.

The sponge city concept is neither uniquely Chinese nor new in India, given the Indian way of life where communities learnt to live with water, and its fury, for ages. For example, the Koli community in Mumbai knows how to read the sea and its many moods. But it is a timely reminder about how our cities should be built or rebuilt, especially when studies have shown that natural methods are up to 50 per cent more affordable and 28 per cent more effective than human or engineering solutions.

Mumbai still has some water bodies and green areas that can help convert it into a sponge infrastructure, wrote architect Shreya Rangaraj, and she recommended identifying and defining varying degrees of wetness across its landscapes, with each degree representing a specific threshold of sponginess, from maidans and neighbourhood parks as the first to restoring water networks of creeks and rivers as the fourth. Chennai, Kochi and Ahmedabad had started out on modest experiments with the sponge city concept; there’s no reason why Mumbai and Kolkata should not.