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Mumbai: the "rain ready" city that floods every year

Source(s):  Acclimatise

By Devika Singh

This year, as in the years prior, the city of Mumbai was inundated by floodwater. Mumbai International, the country’s busiest airport was water logged and over a quarter of all flights were affected. The National Disaster Response Force and Indian Army were called upon to evacuate 2000 passengersstranded on the Mumbai-Vadodara train at Nalasopara and a further 400 salt pan workers and their families, stranded on a passenger train at Palghar. The severity of the impacts of flooding in the city demands an equivalent response, but this has not been forthcoming. The Brihanmumbai Municipal Corporation (BMC) is responsible for health, sanitation and water infrastructure spending in the city. Three years ago, after having spent INR 200 crore (USD 29.148 million) to build a new pumping station, the BMC proclaimed that Mumbai was now ‘rain ready’. To the contrary, Mumbai’s floods now reliably occur each year.

The BMC is India’s wealthiest civic body, with an annual budget often exceeding that of some states in the country. Its budget for 2017 was INR 25,141 crore (USD 3.664 billion). However, less than 18% of that budget was allocated to civic infrastructure (including upgradation of sewage and storm water drainage systems), in spite of the city’s much-publicised annual deluge.

However, investment in flood resilience is badly needed. On 24 June 2018, the city received over 150 mm of rainfall over a 24 hour period, 438% over Mumbai’s normal daily average. By July, the city received over half of the season’s rainfall quota, in just under 20 days. The severity of rainfall events is only one factor governing the impact of the floods. Poor urban planning, a lack of infrastructure investment, poor governance by the BMC, and unregulated development, all play their part.

Floods as a window into Mumbai’s past

In order to understand Mumbai’s current flood problems, it is helpful to look to the past. The city was originally composed of seven islands that were converted into the metropolis through extensive construction on reclaimed lands. Portions of the city are 6-8 metres below sea level, with large infrastructure developments dotting the coastline. Several buildings on reclaimed land are just above sea level, some way below high tide levels. Rampant development has taken place along the length of the Mithi river, its surrounding mangroves, wetlands, salt pan lands and flood plains. The wetlands served as a buffer zone, providing protection from flooding and rising tide levels.

Poorly planned construction in these areas has not only made the city more prone to flooding, but has also compromised the safety of the city and its people in the face of extreme events. What was originally Mumbai’s natural river drainage system has now been reduced to less than 50% of its original flow. It has, in effect, become a massive open sewer, carrying silt, waste and plastic through the heart of the city. Mumbai’s man-made drainage system does not fare much better. Built in 1860, during the British colonial era, the underground drainage system was constructed to support the 19th century population of the city and drain 25 mm of rainfall per hour, at low tide. Rainfall exceeding that limit, combined with high tide, results in the familiar picture of a flooded Mumbai.

Flooding’s deadly impact

In August 2005, Mumbai witnessed one of its most devastating floods. Around 500 people died over a matter of days. Some estimates of total economic losses reach up to INR 28 billion (407.9 million USD), INR 10 billion (145.6 million USD) was just infrastructure damage. Railway services, local trains, roads, and the airport were all inundated, and the city was brought to a standstill. The Mumbai airport, built on reclaimed land from the Mithi river, was inundated for three days.

Jump to August 2017: the city continues to struggle with flooding. Once again, the city’s critical infrastructure services such as transport and telecoms were disrupted. Floodwaters caused a Spice Jet flight to over shoot the runway and get stuck in the mud. The airport was closed for almost a day due to water logging. These scenes were repeated earlier this year, when an Air India flight overshot the runway, and flooding saw 89 arrivals and 319 departures from the Mumbai airport delayed.

In the wake of a flood disaster, it is the poor and slum dwellers who are worst affected. In 2005, the poor residents of Mumbai faced 60% more loss than their richer counterparts. Losing the little they have can cause irreversible damage to health, livelihood and life for these communities. In 2017, and now in 2018, the slum areas of the city remain the most affected.

The northern suburbs of Mumbai have faced a power cut for 37 hours, streets and railway lines have been water logged and cracks have been spotted on the Saket bridge. The city’s restricted drainage capacity is illustrated by Thane, a neighbouring district and part of the Mumbai Metropolitan Region. Thane flooded in spite of experiencing a 27% rainfall deficit this season (the only area in Mumbai to receive a deficit). This is indicative of the extent of under-capacity of the drainage systems, where even a lower than average rainfall incident can cause flooding. While overall rainfall amounts may have dropped, increased intensity of rainfall events in a short span can overwhelm the current drainage capacity of the metropolitan area.

The Brihanmumbai Municipal Corporation (BMC)

Every year before the rains hit, the BMC makes a last-minute attempt to de-silt and clean up the city’s natural and man-made drainage systems. And every year, the BMC fails. After the devastating floods of 2005, the BMC allocated INR 2500 crore for BRIMSTOWAD (USD 364.2 million) the Brihanmumbai Storm Water Disposal System. By 2017, the cost of the project had increased to INR 4500 crore (USD 655.74 million). Thirteen years after the drainage system was first approved, a majority of the city’s low-lying areas and slum settlements are yet to receive any respite from the annual deluge.

During the 2011 floods, the BMC commissioned 8 pumping stations along with 58 other projects. Today, in 2018, only 5 pumping stations are operational, and less than 30 of the planned flood protection projects are complete. In 2013, the BMC committed to spending INR 1400 crore (around USD 204.01 million) on setting up sewage treatment plants along the Mithi river. While the money has been spent, the Mithi remains an open sewer coursing through Mumbai. In 2015, having spent INR 200 crore(USD 29.148 million) to build a new pumping station, the BMC claimed that the city was now ‘rain ready’. And yet again, Mumbai flooded.

Climate change: What future for Mumbai?

One study of the Konkan coast from Dahanu to Vengurla (just north of Mumbai) over the past 20 years has shown a sea level rise of 5-6 cm. This has led to sea water intruding up to 1 km inland, causing damage to farm land and mangroves. Studies indicate tidal patterns are becoming more erratic, while precedent shows us that civic bodies and infrastructure are not prepared for these changes. The standard response has been the construction of bunds. These prove expensive and inefficient, costing around INR 60,000 per metre (USD 874.32) of bund construction. Further, they are built only in sections, thus providing limited protection against extreme events.

Some climate change projections indicate that around 40% of Greater Mumbai could be underwater by the end-century due to continuing sea level rise. Sea level rise is projected to increase by between 24 and 66 cm for Mumbai. Monsoon rainfall for the Konkan administrative division of Maharashtra (includes the Mumbai Metropolitan Region) is projected to increase by between 10% and 30% by mid-century (2021-2040). Annual mean temperatures for the same time period are projected to increase by 1.1°C-1.28°C. Warmer air can hold more water, increasing the likelihood of more intense rainfall events and longer dry spells between intense rainfall events.

In 2014, the Maharashtra State Action Plan on Climate Change identified that a repeat occurrence of the 2005-like rainfall event would flood a number of areas (especially the low-lying areas) in the Mumbai Metropolitan Region, even after the drainage capacity is expanded. This goes to show that the steps taken by the BMC towards flood resilience are not sufficient to prepare the city for future climate-related extreme events. The BMC needs to integrate climate change adaptation strategies into its policy decisions, if it wants to avoid a repetition of the 2005 flood impacts. The State Action Plan has a number of recommendations to improve Mumbai’s adaptive capacity to floods and extreme rainfall. Foremost amongst these are strengthening of the storm water drainage network and improving ground water percolation. Improving coordination between identified implementation agencies such as the Disaster Management Department, Storm Water Drainage Department and the BMC would go some way towards making Mumbai ‘rain ready’.

Rising sea levels will result in increasing salinity of coastal groundwater, endanger wetlands and inundate valuable land, directly affecting the lives and livelihood of coastal communities. Projections made by an ADB study indicates that total losses in Mumbai could as much as triple by 2080 as compared to the present. Another study estimates that the probability of a flood event (similar to the 2005 incident) is likely double, with a tripling of losses (direct and indirect), amounting to $690-1890 million by 2080. And these estimates do not consider potential loss of life.

The historical trends and future projections all point to increasing intensity of rainfall, rising sea levels and an increase in extreme weather events. The high population density of Mumbai, growing development on reclaimed lands, under-capacitated drainage systems overburdened with garbage and plastics, combine to exacerbate the effects of rainfall events and climate change. These factors suggest that a recurrence of the 2005 floods is a matter of ‘when’ not ‘if’. The city has some tough decisions to take, but to begin with, improving the drainage system alone can reduce losses by as much as 70%. In addition, extending insurance coverage could halve the indirect losses that emanate from Mumbai’s annual floods.



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  • Publication date 08 Aug 2018

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