Urban flooding crisis: Why Indian cities face monsoon mayhem every year

But recent precipitation trends, driven by climate change, have drastically changed. According to Dr Rajeevan Madhavan Nair, former Secretary of the Ministry of Earth Sciences, while the total rainfall across the country has not shown a clear long-term trend on a national average, there are large spatial variations. He also noted that the frequency of extreme rainfall events, especially those over 150 mm in a day, are becoming more common, rising by about two events every decade, as per Press Information Bureau.

The IPCC Sixth Assessment Report (2021) cautioned India to expect more short-duration but intense storms, especially in urban areas with low drainage absorption capacity.

Bengaluru Urban district, for instance, has been said to be the most prone (0.57 vulnerability index) to flooding among all districts in south India, based on data collected by Indian Meteorological Department (IMD) between 1969 and 2019.

In a report in The Hindu, A Prasad, scientist, IMD Bengaluru attributed this to increasing urbanisation and heavy rainfall in a short period of time.

“Bengaluru generally gets heavy rainfall, along with thunderstorms in a short period of time. Such thunderstorms are reported most often in May and September. During an inundation episode in Bellandur in 2022, the city received 80 mm of rainfall in just one hour. This kind of rainfall will definitely cause flooding,” he said.

Disappearing natural water bodies

Cities such as Bengaluru and Chennai boasted extensive water systems such as lakes, wetlands, and storm channels that could drain heavy rainfall. But haphazard urbanization has been constructed over these. Bengaluru had 262 lakes in the 1960s, which have fallen to a mere 80 operational ones. More than 93% of the city's surface area is now covered with structures, and water-spread area has fallen from 2,324 hectares to as little as 696 hectares, according to a study last year by Indian Institute of Science, Bengaluru.

Chennai fares worse. The wetlands decreased from more than 600 in 1970 to a mere 27 in 2015, based on environmental estimates. This huge reduction in ecological buffers implies that even normal monsoon periods cause perilous surface runoff and flash floods.

Dilapidated, disorganized drainage

Stormwater systems of today need to take into consideration rising rainfall, population growth, and suburbanisation. Yet, most Indian cities continue to employ narrow, choked, and frequently illegal or unofficial drains. And worse, stormwater drains in most places also transmit sewage, as a result of gaps in sewer networks. In Delhi and Patna, the double system poses grave sanitation risks during floods.

"With time, all the assumptions of drainage are broken," says Prof. Gosain. "The city spreads out, land use patterns alter, and drains become clogged by silt and solid waste." He also explains that most drains are now inaccessible since they are permanently covered by concrete, making cleaning and desilting impossible.

The problem isn't bad design, it's bad maintenance. For example, Chennai removed 67,000 of its 100,000 silt pits ahead of the 2025 monsoon, part of a ₹22 crore initiative to fit new stormwater drain packages, as per Down To Earth. But this initiative isn't equal or sufficient across cities.

Concretisation, less natural slopes

Stormwater drains use natural slopes extensively to transport water through drains by gravity. However, as the cities expand chaotically, urban construction has pushed into low-lying areas and underpasses that defy gravity-driven drainage. In those areas, water must be pumped out, which necessitates continuous electrical power supply and working pumps, both of which break down in severe storms.

In urban areas such as Gurugram, this has resulted in new measures such as modular rainwater tanks that store up to 2 lakh litres of rainwater in green belts and other public places. According to officials quoted by The Times of India, these are potentially more efficient than the previous 7,000-litre chambers.

Sponge city

To counteract this, cities such as Chennai are now investing in sponge city engineering, an intervention that employs permeable pavements, eco-blocks, rooftop gardens, and underground aquifers to take in and deflect stormwater. Chennai has constructed 57 sponge parks up to 2024. The Greater Chennai Corporation (GCC) had planned to construct 30 new sponge parks across 12 zones during 2024-25, but has so far completed only six of them, according to data shared by the civic body in a report by The Hindu.

The Greater Chennai Corporation is also working to revive lakes and tanks, and develop underground storage systems for excess runoff, as per Down To Earth.

In Ahmedabad, the municipal corporation too has adopted the plan as part of a Rs 250 crore urban flood management scheme to keep natural overflow channels alive, according to The Times of India. In October last year, it was reported that five locations — Bodakdev, Vatva, Odhav, Vejalpur and Vasna — were finalized in the initial phase, with plans to extend the project to 22 locations over the next few years, quoting a senior AMC official. It also said that tenders for the project have already been floated.

The city has only 12.3% green cover and 2.2% blue infrastructure (lakes) and desperately needs this initiative as its existing stormwater drainage system serves just 55% of the area, leaving several regions prone to urban flooding.

Investments

Realizing the magnitude of the crisis, the government of India in 2024 made a $300 million (Rs 2,500 crore) urban flood mitigation programme announcement, aimed at preserving water bodies, upgrading drains, and the placing of early warning systems in cities such as Mumbai, Bengaluru, and Pune, as per a Reuters report last year.

Independently, the World Bank sanctioned a $426 million (Rs 3,700 crore) loan to assist Bengaluru in restoring 183 lakes, enhance catchment-based drainage, and establish real-time flood alerts, according to The Times of India.

Urban flooding a design failure

As Prof. Gosain stresses, one cannot wish away the flood but the impact of the flood can be minimised with improved planning. "We need to minimise the size of stormwater by increasing groundwater recharge, developing underground storage, reviving waterbodies, and preventing their encroachment,” he said.

Flooding in cities is no longer a "natural disaster" but a human-made failure of urban planning. Until Indian cities depart from outdated drainage models, rebuild ecological infrastructure, and conform to climate realities, floods will continue to be an annual ritual of disaster. Experts say solutions are available, investments are beginning to flow but political and bureaucratic resolve to act systemically must catch up with the rising water.