From the Western Expressway Highway if you turn left, you start to see mangroves beyond which lies the Mithi river. Go further towards the Kala Killa bus depot at Dharavi, and you will see a green fence beyond which lies an urban forest. This is the Maharashtra Nature Park that the Maharashtra Regional Development Authority (MMRDA) built with the support of the NGO World Wide Fund for Nature India, starting from 1983. Architect Shriya Bhatia cites this as an example of blue green infrastructure (BGI).
Built on a former garbage dumping ground, the park houses indigenous plant varieties and an artificial pond, and abuts the mangrove ecosystem along the Mithi.
What is blue green infrastructure?
The United Nations has appealed to its member-countries to invest more in ecosystem-based solutions to avert disasters and build climate resilience. Sahana Goswami, Senior Programme Manager (Water Resilience) at the research organisation WRI India, says BGI is a nature-based solution which falls under the larger umbrella of ecosystem-based adaptations.
Blue infrastructure refers to water bodies like lakes, rivers, aquifers, canals and wetlands. Green infrastructure include parks, wooded areas, open spaces, rooftop gardens, etc. Whereas grey infrastructure means built structures of concrete and steel. For example, in the context of water management, this could mean dams, gutters and drains.
BGI provides a service for which we would normally use grey infrastructure, while also offering ecological, social, and economic benefits. Sahana says, “Even BGI is engineered. There is a design characteristic to it, there is a design limit within which it works. But elements of nature are built into it.”
The BGI concept evolved from an eco-centric approach to development. The term ‘green infrastructure’ emerged in the 1990s in the United States. Since 2000, environmental planning systems started incorporating designed green infrastructure as an urban greening measure.
Blue infrastructure uses aquatic elements in urban planning. Taken together, BGI is a planned, interconnected network of natural and semi-natural landscapes, designed to provide a service and improve biodiversity.
BGI has applications in stormwater management, sewage treatment, flood mitigation, heat management, etc. But Mumbai continues to invest in grey infrastructure. For instance, BMC is now setting up seven sewage treatment plants. A BGI alternative would be a constructed wetland that uses natural elements such as algae or microorganisms to decompose sewage.
Grey infrastructure may require less land, a precious commodity in cities, but BGI requires comparatively less energy.
Blue green infrastructure can reduce flooding in Mumbai
Mumbai experienced four extreme rain events between 2010 and 2020, according to WRI India’s analysis. After the hard lessons learnt during the 2005 deluge, the city corporation tried to bolster flood management measures. But these have not been enough.
Owing to climate change, Mumbai now faces intense rainfall in short spells. And the increase in built-up area and impervious surfaces results in more surface runoff, which further burdens the stormwater drainage system.
A study by WRI India shows that between 2000 and 2015, the built-up area in 10 cities, including Mumbai, increased on average by 47% within 20 kms of the city centre and 134% in the peripheries. A large part of this development took place in areas with high groundwater recharge potential. Consequently, Mumbai lost daily groundwater recharge capacity of 21 million litres in the central areas and 75 million litres in the peripheries.
The Mumbai Climate Action Plan (MCAP) acknowledges the urgent need to protect blue and green spaces, and also mentions mangroves as a flood protection barrier. But the BMC has proposed cutting 9,000 mangrove trees to construct the second phase of the coastal road. The project is expected to impact another 51,000 trees. This is despite the MCAP’s projections that Mumbai would be one of the 10 Asian cities with the highest populations subject to coastal flooding by 2070s.
Read more: Mumbai: City planning leaves few open spaces for citizens to breathe free
Mumbai’s current master plan DCPR 2034 also allows concretisation in certain eco-sensitive locations. The section ‘Land Use and Manner of Development’ in the plan allows promenades to be built on the periphery of rivers which are supposed to be no-development zones. These concretised roads would worsen runoff, says Shriya.
Sahana says development plans must become responsive to natural systems, and that stormwater should be seen as a resource.
To reduce the burden on existing drainage systems, we need to slow down the rainwater falling on the ground, hold and treat it, and then let it drain away, she says. One way of doing this is constructing bioswales which are ditches with a porous soil layer over which native plants are grown. Bioswales can be built along roads, parking lots, around the edges of buildings, on road medians, etc. They slow down the runoff from streets and buildings, cleanse it and let it into drains.
Water cisterns are another option. These are tanks that collect water from impervious surfaces such as rooftops. The collected water can be used for non-potable purposes or gradually drained out.
Rooftop gardens and rain water harvesting systems can also reduce runoff.
Blue green infrastructure for heat mitigation
Mumbai has also been grappling with increasing heat. According to MCAP, Mumbai’s temperature increased 0.25oC per decade between 1973 and 2020. Ten heat waves and two extreme heatwaves were observed in this period. In 2025, heat waves hit Mumbai as early as February.
Buildings, paved surfaces and concretised roads absorb heat instead of reflecting it, increasing land surface temperature. BGI can offer solutions to make Mumbai heat-resilient. Studies show that vegetation, especially a diverse variety of trees, leads to a drop in temperature.
For urban greening measures to be successful, BMC should prioritise wards with the least green cover. Shriya says that they should also align their plan with the natural ecosystem. She points out that BMC’s current approach sometimes contravenes this – for example, constructing big gazebos and concrete jogging tracks in gardens. She suggests looking at alternatives like compacted mud walking tracks, cluster plantations with indigenous varieties that support biodiversity, and avoiding water-intensive greening like lawns and monoculture.
Read more: Summer is no fun: The silent toll of heat on children
What BMC and citizens can do
The successful incorporation of BGI requires collaborative action. Pankaj Joshi, Principal Director of Urban Centre, Mumbai, a collective which fosters urban design research, says various departments of the BMC should work together towards a larger vision, and not in silos. For instance, currently the Storm Water Drain department (SWD) desilts or widens drains to prevent flooding. But the Building Proposal Department gives building permissions which leads to an increase in the built-up area, and hence runoff, skewing the calculations of the SWD department.
The MCAP too mentions the need for a collaborative effort between the BMC, MMRDA, and the state government to conserve natural ecosystems.
Additionally, community involvement is crucial in setting up and protecting BGI. Citizens should recognise that these systems work to their advantage and should ask elected representatives to protect these, says Sahana. For example, they can involve themselves in protecting local lakes and rivers.
Besides, individuals can create nature-based solutions for heat and flood mitigation in their own premises, such as setting up rain water harvesting systems in their buildings, rooftop and vertical gardens, and growing plants in their balconies. Such small steps too can lead to sustainable cities.
Also read:
- Pockets of greenery and recreation: How Mumbai is claiming its open spaces
- MCAP: Initiated in 2022, how effective is plan to mitigate climate change in Mumbai?
- Mumbai floods once again. Will BMC’s climate budget help?
- Reviving the Dahisar: Are the BMC’s efforts enough to save the river?