Towards flood resilience and water security for Mumbai city

Mumbai is drafting a Climate Action Plan, led by the Municipal Corporation of Greater Mumbai (MCGM) and the Ministry of Environment & Climate Change, Government of Maharashtra, scheduled to be completed by the end of the year. The MCAP will serve as a systematic framework to measure impacts and guide the city towards low-carbon, resilient and inclusive development pathways. WRI India has been engaged as a knowledge partner for this endeavor.

The Plan will focus on six key action areas to build sector-specific strategies for mitigation and adaptation. This blog looks at the ‘Urban Flooding & Water Resource Management’ action area

Water is a crucial resource for Mumbai. It is not only a socio-economic requirement, but also part of the city’s ecological fabric. By studying this resource through a climate lens, this blog reflects on the challenges the city faces with respect to flooding and water resource management and what needs to be done to build resilience for long-term sustainability.

Risk of flooding and impact on water supply services

Studies indicate that extreme climatic events have become a regular feature in the recent past. Based on Indian Meteorological Department’s weather station data, Mumbai on an average has experienced four extremely heavy rainfall events each year in the last decade.

Figure 1: Increasing trend of extreme rainfall events in Mumbai (2011-2020)

Source: IMD AWS-ARG station network (http://aws.imd.gov.in:8091/)

Historically, the city has been built on land reclaimed to join the original seven islands, which has resulted in several pockets of low-lying regions which are prone to water logging. As per the BRIMSTOWAD (BrihanMumbai Storm Water Drainage) report which suggests measures for augmenting the Storm Water Drainage System, the city is capable of handling 25mm per hour rainfall during low tide. If the current trend of increasing extreme rainfall continues, efforts towards flood mitigation must be scaled up drastically. 

When high tide coincides with heavy rainfall, the city is prone to coastal inundation, making informal settlements highly vulnerable. Figure 2 shows ward-wise temporary shelters accessible to the households within 1 km of walking distance in the city of Mumbai (MCGM, Census 2011). The map in the inset denotes the locations of temporary shelters, which shows a denser availability of flood shelters in several flood prone areas in central Mumbai and eastern and western suburbs. However, more flood shelters can be provided in areas that fall outside the 1km walking radius, especially for residents living in slum settlements. With natural and open space coverage of about 31%, the city will also need to assess its contribution in reducing flood risk.

Figure 2: Population having accessibility to flood shelters (Inset: location of temporary flood shelters)

In the event of intense rainfall, water supply is one of the earliest services to be hampered. Mumbai’s primary sources of water such as Upper and Middle Vaitarana, are located more than 100 km away, which accounts for 97% water supply to the city. The water is further distributed through a dense network of main pipelines running 4000 Kms(MCGM Draft Development Plan, 2034). Currently, 96% of Greater Mumbai has been provided with metered connections, of which only 62% is billed. However, slum residents bear the brunt of sharing the connections among 15 households. Lack of metered connections in slum settlements has resulted in an informal market for tanker water. According to a WRI study in 2019, one tanker truck is almost 52 times more expensive than piped water in Mumbai city.

MCGM has been making efforts toward mitigating the risk of flooding and building the city’s resilience. For e.g., the Corporation is reconsidering the construction of Gargai and Pinjal dams, which came with a huge cost of deforesting 1,130 hectares and displacing several families in the catchment areas. Instead, the city administration is looking at desalination and treatment of sewage water within the city limits. Under the ‘Majhi Vasundhara’ campaign, the civic body is actively promoting rainwater harvesting to reduce run-off and restore groundwater level. However, the city needs to scale up its efforts to build resilience while ensuring service reliability.

Sanitation for health and well-being

Maintaining good health has achieved greater significance since the start of the COVID pandemic. The provision of sanitation services is inescapably linked to the health of urban populations. In the last decade, though there has been only a nominal increase of 22.23% (MCGM data) in the sewage generated in the city, only 58.3% of households have latrine within premises (Census 2011). This makes the population living in slums at higher risk of sanitation-related diseases.

The way forward

Understanding the current scenario, to achieve climate resilience, the approach seen in Figure 3 can be adopted.

Figure 3: Approach to building climate resilience in water sector of Mumbai city

Improving access to services is one of the key solutions to reducing vulnerability in informal settlements. Expanding infrastructure can ensure that water is made available to remote locations in slum settlements, but stringent policies need to be implemented to avoid inequities due to informal water supply through tankers.

Real-time data monitoring can support informed decision making, better planning and implementation of supply and sewage related projects in the city. Assessing past climate trends and future scenarios will help in understanding increasing vulnerabilities and developing suitable adaptation strategies and action plans. These strategies need to integrate nature-based solutions for improved land-use practices and urban planning.

Considering the current infrastructural challenges, changing rainfall patterns and future water demands, the city will need to adopt a holistic approach to water resource management. Mainstreaming flood risk mitigation into their developmental planning will help in better planning for future.

This blog is written by Prutha Vaze

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