Climate Change
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preserving wetlands to fight urban flooding in india

July 24, 2020
Kolkata in West Bengal

India’s biggest challenge in front of its growth is the impact of climate change on its populace. The country has seen unprecedented climatic conditions which have drastically created havoc in the lives and livelihoods of the people.

Cities in India are steadily witnessing migration from climate change affected regions to urban areas in cities. The cities from Mumbai to Patna are grappling with urban flooding scenarios with no solutions in sight. The natural wetlands hold the key to address this man-made disaster of city flooding.

Recently, India is singled out by Oxford Economics, a global forecasting firm, as following a particularly ruinous trajectory with GDP falling 90 per cent by 2100 if improvements are not done in current faulty climate policies

Climate change and increase in temperatures are the major cause for worldwide economic inequality and it will adversely impact the tropical nations all around the globe which also has the greatest number of developed and under-developed nations in this zone.

The Oxford Economics study divided the nations on either side of 15° Celsius, the global sweet spot of economic activities, as nations whose average annual temperatures are cooler than 15°C including those in North America and Europe stand to benefit slightly in the short term from the rising temperatures whereas Tropical and Sub-tropical nations whose average temperatures are already warmer than 15°C today including the entire global South face catastrophic degradation (Bloomberg, n.d.).

Problems in Indian cities

India as a developing nation having a huge landmass (seventh-largest in the world) has the most to lose from this temperature change, as according to a study done by Mckinsey Global Institute, extreme heat will significantly lower the outdoor working capacity of India’s labour workforce in the next three decades, also average loss in daylight working hours putting between 2.5-4.5 per cent of GDP at risk annually (Bajaj, n.d.).

Due to pollution and heat from buildings, cities are usually at a higher temperature than rural areas, as the global increase of temperature of 2° can lead to 4-5° rise cities the effect is also called as Urban Heat island, which is a consequence of anthropogenic activity adding to the climate change also increase in heat can create conditions for the growth of bacteria, virus and other parasites which can be difficult to handle. Cities tend to experience heat waves that affect human and animal health leading to heat cramps, sleep deprivation and increase mortality rates.

The city has high surface run-off (flow of rainwater over the land surface) due to high paved and cemented land surface which lowers the chances of rainwater penetration thus leads to the lower groundwater table and water crisis can be experienced in the long run as recently reported in Chennai and Bengaluru city.

Urban Flooding also occurs in the city due to poorly designed infrastructure lead to high economic loss and tend to affect the vulnerable population in cities for diseases outbreak and mass displacement.

What Are Wetlands ?

“Areas of the marsh, fen, peatland or water, whether natural or artificial, permanent or temporary with water that is static or flowing fresh, brackish, or salt, including areas, of marine water the depth of which at low tides does not exceed six meters.” (Ramsar Convention 1971).

A transitional state between land and water body in other words land saturated with water which is found commonly in every part of the earth where there is a river basin, earth has six percentages of its areas under wetlands.

These water bodies are mostly neglected by residence and authorities for generations as the construction of buildings or any other development cannot take place for its soft and easily amiable soil. They have also been avoided for being dirty and smelly, which also made it an unfavourable place for residential development.

Wetlands as Solution – East Kolkata Wetland

One place which has successfully adopted urban wetlands is Kolkata city, the East Kolkata Wetlands have been a part of the city system acting as the main drainage system. Also known as Salt lake, it acts as a flood cushion for the city it also generates fish and vegetables for the state, along with providing employment to nearly twenty thousand underprivileged families. East Kolkata wetland also treats sewage of Kolkata city which is estimated to be 1100 million litres daily.

Timeline of East Kolkata Wetland

After the inception of Calcutta City by Job Charnock bordering the wetlands in the eastern fringes and used only for defence purposes. British authorities in 1690, discharged municipal wastes without treatment to the Hooghly River, leading to the outbreak of Malaria, Cholera, etc as it was the source of domestic water for the city.

To solve the problem William Clark, Chief Sanitary Engineer, proposed deposition of wastewater in the ‘salt lakes’ which started in 1868 and in 1876 Nandalal Das and Durga Charan Kundu leased this land for growing vegetables and fishery, as B. N. Dey in 1943–1944 increased the availability of wastewater to these wetlands, widespread adoption of wastewater-fed aquaculture started which supplied the state with fishes and became high economic value which is still prevalent this day.

Sarmila Banerjee & Debanjana Dey, 2017. Eco-system Complementarities and Urban Encroachment: A SWOT Analysis of the East Kolkata Wetlands, India, s.l.: Cities and the Environment.

Services offered by Wetland

  • Treatment of sewage:-The city gives out 1112 MLD of wastewater annually with 2802 ML per year increase and EKW treats 78 per cent of it saving an enormous amount of ₹4680 million/year, providing an “Ecological subsidy” for the city, the annual budget of Kolkata Municipal cooperation Sewage and Sanitation department is ₹1693 million, for this reason, these wetlands are also called “Kidneys of Kolkata City”. (Sarmila Banerjee & Debanjana Dey, 2017). Small Bheris (ponds made by embankments) are used to breed pawns, these feed on the organic matter contained in the incoming sewage water thus purification of water takes place along with the production of fresh fishes which accounts for 40 per cent of the entire state, the purified water is then used as irrigation in paddy fields producing 22 per cent of it every year and sustaining a livelihood for thousands of underprivileged families in the region.
  • Ecological Sustenance:– Ramsar Convention values wetlands at 12.8 million/ km.sq, this high value is assigned cause as they are used for flood control for their ability to absorb excess water (Mumbai incurs a loss of Rs 14,000 crore due to floods), lowering of greenhouse gases which is very useful for industrial cities, purification of air, carbon sequestration, acts as a habitat for many rare species especially migratory birds and potential for recreational space.
  • Climate Regulation:- The wetlands have the capacity of creating a micro-climate around its surrounding which lowers the temperature and bioremediation (detoxification) takes place, rich biodiversity flourishes with about 100 plant and 20 mammals species recorded in the region facilitated by the process of eutrophication. Natural recharge of aquifers also takes place by capturing the rainwater through surface run-off from the city


The co-existence of an organically active water body inside a city will provide the necessary balance and mitigate the hazardous component of city development.

Wetlands as UN-Habitat states that the ecosystem services and benefits provided by a wetland is more than any other ecosystem. The benefits that are surmounted on the surrounding environment by the presence of a wetland is comparable to the services provided by a rainforest.

Wetlands are among the world’s most productive environments and are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival.

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