Mumbai needs reliable drains and pumping systems. But its next generation of flood management must also slow, store and absorb rainwater before it reaches the drainage network.
Every monsoon, Mumbai's flooding is framed as a drainage problem. The familiar responses follow: Desilt drains, remove waste, repair or widen channels, increase pumping capacity and improve stormwater outfalls.
These measures are necessary. Mumbai needs reliable drainage infrastructure.
But a deeper question is becoming unavoidable: Can a city continue to manage increasingly intense rainfall simply by trying to move water away faster?
Mumbai's flood risk is shaped not only by the capacity of its drains, but also by what happens to rain before it reaches them. Roads, buildings and pavements have replaced soil and vegetation across much of the urban landscape. Open spaces, wetlands, ponds and natural drainage systems have been reduced or altered. During intense rainfall, more water becomes surface runoff, reaches drains more quickly and places greater pressure on infrastructure.
This is why Mumbai needs to think beyond a drain-first approach.
The answer is not to abandon conventional drainage. It is to combine it with what is increasingly known as blue-green infrastructure (BGI): Systems such as permeable pavements, rain gardens, infiltration trenches, green roofs, wetlands, detention areas, restored water bodies and vegetated drainage channels that can slow, store, infiltrate or temporarily retain stormwater.
My research examined whether such an approach could work in Mumbai not as a substitute for drains, but as a complement to them.
{{/usCountry}}My research examined whether such an approach could work in Mumbai not as a substitute for drains, but as a complement to them.
{{/usCountry}}The research brought together three questions: What the international evidence says about implementing BGI; whether strategically located BGI can reduce runoff and flooding in Mumbai; and whether the city's municipal institutions are ready to implement it.
The first study reviewed 797 publications and selected 42 for detailed analysis. Only 26% of the studies focused on developing-country contexts, and none specifically addressed India. The review identified eight factors that influence BGI implementation, including spatial planning, policies, stakeholder perceptions, barriers to adoption, local-government capacity and scientific research.
The message is important for Mumbai: BGI is not simply a matter of installing rain gardens or permeable paving. Its success depends on where interventions are placed, how they are designed, how they interact with existing drainage, who maintains them and whether municipal institutions have the capacity to manage them.
The second study tested this proposition in two Mumbai wards, F/North and G/North, using geospatial analysis and EPA-SWMM hydrological and hydraulic modelling. The study examined interventions including permeable pavements, infiltration trenches and green roofs under a simulated 25-year return-period extreme rainfall event.
The results provide a useful indication of what a hybrid approach can achieve.
In the modelled scenario, the proposed BGI interventions reduced peak runoff by 12.6% and total runoff volume by 5.5%. More strikingly, the peak flooding flow rate fell by 45%, from 94.1 to 51.7 cubic metres per second.
These numbers should not be interpreted as a promise that BGI will reduce flooding across Mumbai by 45%. The modelling covered specific wards, selected interventions and one rainfall scenario. BGI performance will vary with rainfall intensity, soil and groundwater conditions, available space, maintenance and the way individual interventions interact with the drainage network.
But the result demonstrates something important: Strategically placed interventions can change the timing and intensity of stormwater reaching the drainage system.
That matters in a city where a drainage network can be overwhelmed by intense rainfall within a short period.
The objective, therefore, should not always be to make every drain larger. In some locations, part of the solution is to ensure that less water reaches the drain at the same time.
There is, however, another challenge. Even if Mumbai knows where BGI could work, who will plan, approve, construct and maintain it?
My third study examined knowledge and perceptions of BGI among officers in the Municipal Corporation of Greater Mumbai's (MCGM) Storm Water Drains, Planning and Gardens departments. The study found strong awareness of flooding and considerable willingness to consider BGI, but more uneven technical familiarity with its hydrological performance, multifunctionality, implementation requirements and limitations during extreme rainfall.
The survey of 26 officers found that willingness to implement BGI was considerably higher than levels of BGI knowledge. Planning officers showed comparatively stronger conceptual understanding, while the Storm Water Drains and Gardens departments showed strong willingness to implement such measures despite lower technical familiarity.
That gap is significant.
BGI sits between conventional departmental boundaries. A permeable footpath is simultaneously a road intervention, a stormwater intervention and a landscape intervention. A detention area may involve planning, engineering, parks and maintenance. A restored water body has implications for drainage, ecology, land use and public space.
If each department considers only its own infrastructure, BGI risks becoming a series of isolated projects rather than part of an integrated urban water system.
The institutional research, therefore, points to a simple requirement: Mumbai needs capacity to plan blue-green and grey infrastructure together.
The first step should be to plan at the level of catchments and wards, rather than treating every flooding location as an isolated engineering problem.
Detailed spatial and hydrological assessments can identify where water accumulates, how it moves through a catchment and where there is realistic potential for temporary storage, infiltration or controlled release. These assessments should consider land use, slope, elevation, soil and groundwater conditions, drainage networks, flood hotspots, public open spaces, road corridors and existing water bodies.
Second, BGI should become part of routine infrastructure investment.
When roads and footpaths are reconstructed, when parks are redesigned, when public buildings are developed and when drainage infrastructure is upgraded, the question should be asked: Can this project also help manage stormwater?
A footpath, for example, does not have to be merely a pedestrian surface. Where conditions permit, its design could allow it to receive and temporarily retain runoff. A road median can potentially accommodate infiltration or detention features. A public building may offer a suitable roof for rainwater retention or a green roof. A park can sometimes function as temporary stormwater storage without losing its primary recreational purpose.
The third priority should be demonstration projects with monitoring.
Mumbai should test BGI in different urban settings rather than assuming that one intervention will work everywhere. Performance should be measured through rainfall, runoff, water levels, maintenance requirements and costs.
This is particularly important because BGI is not automatically successful simply because it has been constructed. A poorly designed or poorly maintained intervention can underperform. Local evidence can help MCGM develop design standards based on Mumbai's own rainfall, soils, groundwater, density and maintenance conditions.
Fourth, every intervention needs an institutional owner.
Who maintains a rain garden after construction? Who clears a permeable pavement when sediment accumulates? Who monitors a detention area? Who pays for repairs?
These questions sound administrative, but they can determine whether BGI functions for years or becomes another under-maintained urban asset.
Finally, Mumbai needs department-specific technical capacity.
Engineers need to understand how BGI interacts with drainage networks. Planners need to understand catchments and hydrology. Landscape professionals need to understand stormwater functions. Maintenance teams need practical guidance on inspection and upkeep.
General awareness is not enough. Implementation requires people with the skills to design, approve, construct and maintain hybrid systems.
Mumbai's challenge is not that it has drains. It is that the city increasingly asks those drains to receive water from an urban landscape that has fewer places to absorb and temporarily store it.
The next phase of flood management should, therefore, be based on a different principle: Do not only move water faster; make space for it.
That does not mean replacing drains with wetlands or expecting rain gardens to solve Mumbai's flooding. During extreme rainfall, conventional infrastructure will remain indispensable. Pumps, drains, outfalls, holding ponds and other engineered systems will continue to carry much of the burden.
But grey infrastructure can work more effectively when it is supported by a landscape that slows runoff before it reaches the network.
Mumbai has an opportunity to move from a largely reactive approach finding where water floods and trying to remove it to a more integrated approach that asks where water can safely stay, even for a short time.
The modelling evidence from F/North and G/North suggests that strategically located BGI can reduce runoff and peak flooding flows under a defined extreme-rainfall scenario. The institutional research suggests that there is interest within the municipal system, but that technical capacity and coordination need strengthening. The broader literature shows that successful BGI requires planning, policy, institutional capacity and locally appropriate evidence not just individual projects.
The lesson extends beyond Mumbai. Indian cities facing increasingly intense rainfall cannot rely on a single type of infrastructure. They need urban water strategies that combine engineering with planning and ecology.
The question for Mumbai is no longer simply how to drain the next downpour.
It is how to build a city that gives the rain somewhere to go and somewhere to stay before it becomes a flood.
(The views expressed are personal)
This article is authored by Vedanti Kelkar, doctoral candidate, Faculty of Environmental Sciences, Technische Universität Dresden, Germany.