Mumbai Floods
2005 to 2017

By Vishal Anand

Mumbai Floods 2005 to 2017

Why does the story keep repeating itself?  

A 2015 report by the UN Office for Disaster Risk Reduction (UNISDR) estimated that flooding in India causes an average economic loss of $7 billion annually, with Mumbai – India’s financial capital, possessing a total wealth of $82 billion – contributing substantially to the losses. On August 29th, 2017, Mumbai received 200 mm of rainfall in 12 hours: the equivalent of 11 days of average daily monsoon rainfall in half a day. The rains brought the city to a standstill for about a day, disrupting road, rail and rail travel, and causing damages to life and property.

This was called the worst case of flooding since 2005.  In 2005, in just 24 hours, Mumbai received 944 mm of rain. The floods caused the death of over 500 people and halted business activities for days. The floods caused direct economic damages estimated at almost two billion USD. Insurance agencies paid Rs. 3,000 crores that year to vehicle owners and shopkeepers. Research indicates that the intensity of similar extreme weather events is increasing. Climate change projections clearly indicate an increase in high-intensity rainfall, and that precipitation events greater than 100 mm have dramatically increased in number over the past 100 years.

Why is flooding an annual phenomenon in Mumbai?

Historically, Mumbai has been predisposed to flooding, albeit in a less drastic manner; records corroborating it have been found in old Portuguese and British journals and gazettes. Being a coastal city, its flooding is also tightly linked to the tidal movements. In the previous century, there was a large belt of mangrove swamps along the periphery of the city that served as a critical buffer against the floods. 

Mangroves can reduce storm surge levels by up to half a meter for each kilometer of mangrove forests that the storm surge passes through. Today, given the astronomical real estate prices, the ever-growing population and the increasing scarcity of land, Mumbai has sacrificed its ecology for the sake of development. These mangroves are now in severe decline, with clearly evident consequences.

Mumbai’s drainage system is also designed to be able to manage only about 25 mm of rain per hour. In the suburbs, the drainage capacity is 50 mm per hour through the Brihanmumbai Storm Water Disposal system projects. However, every year, Mumbai records several days of heavy rainfall, exceeding 65 mm per hour, which means that even the proposed enhanced drainage capacity of 50 mm per hour would not be able to accommodate that volume. 

The issue is further compounded by the changing, urban, land-use-pattern that prevents water from getting absorbed into the ground. In areas outside the city, nearly 80% of the rain water is absorbed, and percolates until it recharges the aquifer. In Mumbai that is replete with concrete and tar, impervious areas get artificially created. This inhibits water absorption, that then has no other option but to flow into the already inadequate drains, eventually causing flooding.

Another aspect that reduces the efficiency of drains in urban Indian cities is the use of storm water drains as effluent and sewage disposal systems. Deposits from untreated effluents cause silt to precipitate to the bottom of water bodies, reducing their volume and capacity. This is further compounded by the immense volume of garbage produced by the city, which inevitably finds its way into storm water drains, sewage lines and river systems such as that of the Mithi river, blocking them, and thereby, lowering their efficacy. 

Development and construction of infrastructure on flood-prone areas and along naturally-occurring watershed channels further hampers the movement of water and reduces Mumbai’s resilience to withstanding serious flooding. Thus, the need of the hour is the urgent revival to the pre-existing ecology of the area along with significant improvements in waste disposal, and the implementation of environment-conscious sustainable development practices.

About the author

Vishal Anand is a Research Analyst in the Information Services team of Mitkat Advisory. He graduated from  from St. Joseph’s College, Bangalore,with a Bachelor’s degree in Environmental Science and  from Gujarat Forensic Science University with a post graduate degree in Forensic Science

Disclaimer: Any views or opinions represented in this blog are of the author and do not represent those of MitKat. Any views or opinions are not intended to malign any religion, ethnic group, club, organization, company, or individual.

Published On - Sep 21,2017


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