Mapping how growth in Kochi, Mumbai and Chennai made them flood and drought-prone

Nine maps show how the change in built up area in these three coastal cities at the cost of its natural ecosystems have made them especially vulnerable to extreme weather events.
Mapping how growth in Kochi, Mumbai and Chennai made them flood and drought-prone
Mapping how growth in Kochi, Mumbai and Chennai made them flood and drought-prone

Only a year after what was widely described as a once-in-a-century calamity, Kerala reeled under severe monsoonal flooding in August once again. Intense spells of rain led to floods and landslides with the rains reportedly claiming 125 lives in the state. While it was the northern and hilly districts such as Malappuram and Wayanad that faced the worst of this year’s storms, densely populated urban centres like Kochi were also severely affected. Echoing the 2018 floods, the Cochin International Airport - one of the country’s busiest - had to be closed again.

Following flooding in Mumbai last month and the severe water crisis that the city of Chennai is still facing, the Kerala floods are yet another reminder of the vulnerabilities faced by coastal cities in India. Unplanned urbanisation and encroachment of sensitive ecological areas have weakened the ability of coastal areas to cope with extreme weather events - predicted to become more frequent because of climate change. The impacts on coastal cities are compounded mainly because these low-lying regions are centres of economic activity and home to a large and growing population.

The threat of cyclonic storms also loom large over India’s coastal settlements - Cyclone Fani caused widespread devastation in Odisha in May earlier this year, Cyclone Ockhi impacted south Kerala and Tamil Nadu in 2017 and Cyclone Vardah struck Chennai in December 2016.

An estimated 14% of India’s total population lives along its 7,500-km long coastline that traverses nine states, 77 towns and cities including some of the fastest-growing such as Mumbai, Chennai and Kochi.  Aside from the present danger posed by extreme weather events such as heavy rainfall and cyclonic storms, more slow-onset impacts brought about by climate change also threaten the coastline. A 2016 UN report estimated that 40 million people in India will be at risk from sea-level rise by 2050.

The coastal cities of Mumbai, Chennai and Kochi were home to rich, natural ecosystems of rivers, creeks and wetlands, but these are now encroached with more construction and increase in built-up area. This has reduced permeability of the soil, depleting groundwater reserves, and choked natural waterways and drainage networks, heightening the risk of flooding.

The following maps show the change in built-up area over time in these three cities. These maps were produced as part of a publication by the Indian Institute for Human Settlements (IIHS) Bengaluru, the Urban India Atlas, which visualises the expansion of 100 Indian cities over the past two decades using publicly available data. The first two time points considered are from around the recent census years (2001, 2011) and the third is based on satellite imagery (2016, 2017).


Rapid urbanisation combined with a lack of efficient waste disposal systems have left several waterbodies in the city in poor condition. Blocked waterways and reduced width and depth of canals inhibit drain-off into the Arabian Sea, while the speed and scale of construction reduces the permeability of the ground.

The primary source of drinking water for Kochi is the Periyar river. Untreated sewage from households and industries have severely polluted large sections of the waterbody, leading to water scarcity during the summer. The Periyar was one of the main rivers that broke its banks and caused flash floods in the worst-affected regions of Chalakudy and Aluva, on the outskirts of Kochi city, during the August 2018 floods.

Kochi is embedded in a complex network of rivers, tidal creeks, backwaters, lakes and the sea which are vital to supporting the city’s coastal communities in addition to being effective channels that can drain off water in the event of extreme rainfall. Studies done by the Cochin University of Science and Technology found that canals that were once vital lifelines for the city have been reduced to stagnant, polluted pools, such as the Edappally thodu, Perandoor, Mullassery, Thevara canals. Building over these waterbodies has significantly reduced Kochi’s ability to cope with the monsoon.

The three maps show how Kochi rapidly grew from 2001 to 2008 to 2017, with the built-up area gradually growing over the city’s various interconnected canals and waterbodies.


Mumbai drowning in rains has become almost a routine affair, and being the most populous city in India, its large scale urbanisation to accommodate its population of over 22 million means more built-up area and more encroachment.

The city’s mangroves, rivers and salt pans are effective barriers against flooding, acting as natural storm water drains and buffering heavy rainfall. With Mumbai having one of the largest scale of construction in the country with a strong builders’ lobby, all these natural barriers continue to gradually be encroached upon for more built-up area. An inquiry into the devastating 2005 floods emphasised on the role played by reclamation of land for construction along the Mithi river by clearing large tracts of mangrove forest. The report estimates that Mumbai lost 40%  of its mangroves between 1995 and 2005 with the construction of the Bandra-Kurla Complex at the mouth of the Mithi River being particularly damaging to this natural ecosystem.

In the wake of a landmark judgement by the Bombay High Court in 2005 which banned the destruction of mangrove forests, the extent of mangroves in the city is reported to have improved. The Forest Survey of India says that cover increased from 42 sq. km in 2005 to 66 sq. km. in 2017. However, they remain at risk as large-scale infrastructure such as the Coastal Road project are planned with scant regard for the fragile marine environment.

Mumbai's groundwater levels have depleted over the years with commercial exploitation rampant within the Greater Mumbai area. A district profile prepared by the Central Ground Water Board in 2013 noted that overdrawing of groundwater for commercial purposes and domestic use within housing societies would lead to saltwater contaminating the city’s aquifers. This has already been observed in Colaba, Dharavi and Khar. Borewells reaching up to depths as low as 600-800 feet fail to reach water due to excessive drawing to meet the city’s growing demands.

From 2001 to 2016, Mumbai rapidly grew over its ecologically sensitive areas including mangroves, rivers and salt pans.


While Chennai suffered from large scale flooding in 2015, 2019 has seen the onset of a severe drought in the city, leaving several thousands of residents dependent on erratic private water lorries for their daily needs. This veering between flooding and water scarcity is also related to the city’s uncontrolled urbanisation and poor planning, where the city has consistently grown over its lakes in the past two decades.

Additionally, a large share of the Pallikaranai marshland, an ecologically sensitive zone in the city which was vital to buffering extremes of rainfall has been taken over by construction. An entire IT corridor, apartments, educational institutions, roads and other services have been built over large parts of this marshland, shrinking it from 5,500 hectares recorded in 1965 to 600 hectares in 2013 -- observed in a report submitted to the Madras High Court on August 19. The report also attributed the 2015 Chennai floods to unchecked construction and poor waste management which prevented natural water run-off into the sea.

The growth that has taken place along the coast towards the south of Chennai's city limits indicates rapid construction along two vital ecological zones - the Pallaikaranai Marsh and the Aquifer Recharge Zone.

A key law that has relevance for the protection of coastal cities is the Coastal Regulation Zone (CRZ) notification which sets rules for building along the coast, to protect the ecology by controlling human and commercial activity. The CRZ notification came into being in 1991 and it was then hailed as a landmark step towards installing a comprehensive protective net over the country’s entire coastline. The document demarcated coastal areas into four zones - each with its own development regulations. They have, however, been progressively weakened over the past two decades through multiple amendments. 

Relaxing CRZ rules and allowing for more economic activities in coastal areas puts more people at risk, leading to uncontrolled urbanisation. Violations to CRZ rules are frequent in all three cities discussed here, as pressures from tourism and real estate lead to taking over of sensitive coastal areas.

The need to address challenges faced in the coastal regions was also prioritised in India’s INDC - a key document required to be submitted by signatories of the Paris Agreement in 2015. This pledge identified the need for a National Coastal Mission (NCM) which would focus on conserving the coastal natural environment as well as support livelihoods and address developmental deficits here.

The NCM was thus established by the Ministry of Environment to ensure livelihood security of coastal communities, to conserve, protect the coastal stretches and to promote sustainable development based on scientific principles.

But in the 2019 Union Budget, the National Coastal Mission saw a decline of Rs 35 crore, with an allocation of Rs 95 crore for the present financial year as opposed to Rs 130 crore in the last. Considering the large population that lives in high-risk, vulnerable spots without access to safe infrastructure, this is nowhere close to what is needed to meet the scale of problems affecting coastal regions across the country.

Visakhpatnam, Kochi, Thiruvananthapuram and Chennai are some of the coastal cities that are part of the Smart City Mission, and it is essential that such ambitious programmes do not cause further harm to the already precarious state of these regions, by allowing more construction close to the coast for purposes like tourism, commerce and recreation For instance, an analysis of the flagship Smart City project in Mumbai's Bhendi Bazaar found that this urban redevelopment plan would be detrimental to the natural environment. The plan would lead to a spike in population density placing greater demands on already scarce resources such as water and by increasing the amount of waste generation. In order to deal with urbanisation and its impacts on coastal areas, it is essential that any development programmes in these regions must prioritise ecological protection as well as address grave developmental deficits faced by the urban poor in these cities.

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