When rain turns cities into rivers

Mumbai’s urban resilience was once again on trial as the monsoon unleashed an unrelenting deluge over the city. For days, sheets of rain pounded its streets, forcing the India Meteorological Department (IMD) to issue repeated red alerts. Suburbs witnessed some of the most intense August downpours seen in over a decade, and with high tides locking seawater at the outfalls, vast stretches of the city slipped into a familiar paralysis of waterlogging, stalled transport, and frayed civic nerves.

The deluge not only inundated neighbourhoods but also disrupted the lifelines of the metropolis — crippling trains, choking roadways, and grounding flights. Tragically, casualties have been reported, and emergency responders were stretched thin. The crisis underscores the immediate human and economic costs of extreme weather events in India’s financial capital.

Following the Chitale Committee’s 2005 flood-mitigation recommendations, which called for doubling Mumbai’s storm-water drainage capacity from its century-old norm of approximately 25 mm/hour, gradual improvements have been implemented over the years, yet the city continues to grapple with rainfall intensities that exceed historical design thresholds.

Experts note that Mumbai’s low-lying topography, extensive land reclamation, and the loss of natural drainage channels through urban expansion amplify the city’s vulnerability. Moreover, climate scientists warn that global warming is increasing the frequency of intense cloudbursts and heavy monsoon spells, creating rainfall events that existing infrastructure cannot efficiently handle.

The question, both familiar and urgent, refuses to fade: Why are India’s cities repeatedly caught unprepared for floods despite decades of warnings? Climate change undoubtedly intensifies the monsoon, but it is not the sole culprit. The reckless conversion of wetlands into real estate, the steady erasure of ponds and mangroves, the narrowing of rivers, and the chronic neglect of drainage networks have all conspired to turn heavy rain into urban catastrophe.

Each deluge peels back the veneer of preparedness, exposing the gulf between glossy master-plans and ground realities. The lesson is unambiguous: resilience cannot be improvised once the water rises. Yet the unresolved challenge lingers — can Indian cities recalibrate their planning fast enough to withstand the accelerating fury of monsoons? And more worryingly, are today’s urban policies anywhere close to grappling with the entwined pressures of climate volatility, unplanned growth, and ecological loss?

Not a case in isolation

Each year the arrival of the south-west monsoon now carries equal parts relief and dread. Mumbai is not unique; but as one of the world’s densest coastal metros, the stakes are higher. In the current spell, authorities extended severe weather alerts across the Konkan and districts along the Western Ghats, while Mumbai’s civic body advised people to avoid non-essential travel. Local trains — the city’s lifeline — were curtailed on specific stretches; airport delays and diversions rippled through schedules; and municipal holiday orders closed educational institutions.

When such flooding occurs, the narrative often splits: one side indicts mismanagement; another points to “excessive, unnatural rainfall” driven by a warming climate. The public discourse then pivots to a familiar menu of mitigation projects — underground holding tanks at hotspots, “integrated” flood schemes, or fresh de-silting drives — and to ritual invocations of Mumbai’s “resilience.” Yet this cycle rarely interrogates how the city’s eco-environment has been re-engineered over decades: land reclaimed from the sea, wetlands and mangroves gnawed away, minor water bodies erased, and river channels narrowed — transformations that steadily dismantled natural storage and slowed drainage.

And Mumbai is not alone. Bengaluru’s lakes have been choked by encroachment, Chennai’s Pallikaranai marshland steadily lost to real estate, Hyderabad’s tanks fragmented, and Guwahati’s wetlands drained — each city discovering, in its own monsoon season, how altered landscapes magnify flooding. Together, these examples point to a national urban pattern: water once held and absorbed by natural systems is now released directly and destructively into built-up environments.

Flawed planning

Floods can be anticipated. To claim they occur only due to exceptional rainfall is to underplay institutional responsibility. Hydraulic landscapes are actively produced — by policy, by engineering standards, by what cities choose to protect or pave over. Mumbai’s primary storm-water management programme was envisaged to elevate the design capacity of drains — long constrained near 25 mm/hour — towards 50 mm/hour across suburban precincts, complemented by strategically positioned pumping stations at critical outfalls.

While incremental progress has been registered over the years, the pace and uniformity of implementation have been uneven, and the infrastructure occasionally proves inadequate against the ferocity of short-duration cloudbursts that surpass historical thresholds. Numerous independent assessments and civic studies have consistently highlighted that the system’s design parameters require continual recalibration to remain commensurate with the evolving intensity and unpredictability of the city’s monsoonal regime.

Mumbai’s vulnerability is further accentuated by the city’s complex drainage networks and constrained waterways. The Mithi River, the city’s principal drainage artery, remains a critical choke-point — narrowed in sections, burdened by sediment accumulation, and affected by urban pressures. During this monsoon season, these structural and environmental factors have amplified the impact of intense rainfall, underscoring the intricate interplay between natural waterways and an expanding urban landscape. The consequences during such extreme rainfall events are almost inevitable: with tidal surges keeping seawater levels elevated at outfalls, intense intra-day rain finds limited avenues for dispersal; tracks, subways, and underpasses quickly inundate, bringing the operations of a multi-modal metropolis to a standstill.

Urban flooding is technically complex and politically hard. But cities can — and must — close the gap between rainfall reality and drainage design. Urban flood risk assessments that quantify return periods under today’s rainfall statistics, test green-gray options (from upstream detention and sponge-city retrofits to larger pumps and outfalls), and identify ward-level choke-points can guide scarce resources. They also need to be paired with guardrails: strict buffers around creeks and rivers, no-build zones over culverts and nallas, and legally enforced protection of mangroves and remaining salt-pan wetlands that store water and slow flows.

Lessons to be learnt

Natural hazards cannot be prevented, but the extent to which they escalate into urban disasters is a matter of planning, foresight, and execution. Mumbai’s drainage systems were conceived decades ago, with assumptions that no longer reflect today’s reality of intense, short-duration downpours and rising sea levels. Drains, sumps, and pumping infrastructure must be recalibrated to current hydrological data, and ward-wise performance targets should be publicly disclosed to ensure accountability and allow citizens to track progress.

Wetlands, mangroves, salt-pans, and floodplains are not expendable spaces; they are critical components of urban hydrological infrastructure. Protecting and restoring these natural buffers is as vital as maintaining culverts and pumps, providing a first line of defence against urban flooding. Infrastructure is only as effective as its upkeep, and its design must anticipate the full spectrum of climatic and tidal pressures that the city now faces.

Pumping stations, flood gates, and underpasses must operate in harmony with tidal cycles and forecasted storm surges, linking physical infrastructure with operational foresight. Design standards must incorporate safe-failure mechanisms to prevent catastrophic inundation at critical nodes, as recent airport and rail disruptions starkly illustrate. Advanced meteorological warnings are only useful if they translate into actionable civic advisories, connecting technical monitoring with public response. Closures, diversions, and emergency measures must be issued promptly, with granularity and multilingual accessibility. Effective communication is the bridge between technical preparedness and public safety, reducing casualties and societal disruption when extreme rainfall strikes. Together, these measures form a cohesive framework that makes planning, maintenance, and communication mutually reinforcing pillars of urban resilience.

Cities can further innovate by learning from global best practices, embedding these principles in both design and operation. Rotterdam and Tokyo, for instance, combine engineered “gray” infrastructure with natural systems: Rotterdam’s Maeslantkering storm surge barrier and retention basins mitigate extreme floods, while Tokyo’s underground diversion tunnels channel massive volumes of water away from dense neighbourhoods. Singapore’s ABC Waters Programme integrates wetlands, rain gardens, and bio-retention ponds to slow runoff and enhance water quality. Mumbai could explore localised pilots inspired by these models, demonstrating how international lessons can be adapted to strengthen resilience while improving urban liveability.

Unless cities learn to engage in more nuanced, localised, and comprehensively informed planning and development decisions — grounded in data, enforced by law, and accountable to citizens — urban India will keep reliving this monsoon loop: chaos, relief, and complacency. The 2025 Mumbai floods are not an aberration; they are a verdict on choices long deferred. The only meaningful “resilience” is prevention, achieved through foresight, innovation, and the steadfast integration of natural and engineered systems.

The writer is Associate Professor at VIT Chennai. Views are personal

Published on September 2, 2025