A River named Kolkata
Climate change took its tole on it first victim as Venice was hit by second largest high tide in the recorded history ,turning its street into gushing river of flash flood,a sign that climate change is not a joke now. Like Venice,many coastal cities around the world faces the same fate,especially the ones in the subcontinent of India.
According to climate central study performed by NASA’s Shuttle radar topography misson (SRTM) , they have underestimated the severity of the risk of rising sea level until now. A new research done by a US-based agency claims that more than three and a half crore people in India–as against the 50 lakh estimated earlier– could actually be affected by annual coastal flooding by 2050 and that large parts of Mumbai, and Kolkata could be inundated and practically be under water if global CO2 emissions are not cut drastically.
In another research conducted by Jadavpur University in Kolkata states that Bay of Bengal is rising faster than Arabian sea at a rate of 1.35mm per year. Estimating various parts of Kolkata,specialy low lying areas of Northern part of the city might be completely under water by 2050.
Kolkata had natural defences in form of Ganges river to the west and wetlands to the east which all emptys into the delta region of Sundarbans and then to the Bay of Bengal. The city’s lakes and creeks could absorb the excess rain water along with the help of the soft clay soil that the city stands upon.
But today Kolkata’s old ‘ khal‘ or canal system, which acted as an effective drainage system for some three centuries is in disrepair. Many wastewater conduits out of the city such as storm-water drains, sewers and canals are silted. Gully pits are blocked and hence there is a time lag for water to reach the pumping stations which leads to flooding on the surface. Poor solid waste management, along with an overburden of plastic is the culprit. In the metropolitan part of the city, an area of low lying field which use to absorb the run off water is now filled up to what is now called as New Kolkata. Demise of water boadies , along with rapid extraction of groundwater which causing certain parts of the city to sink further more,leads to the increasing risk of the city going under during the heavy monsoons.
The risk of flooding has increased, as extreme rainfall events have become more common. One study found that Kolkata is receiving many more heavy rainfall days than before.
According to statistic,Kolkata use to receive average rainfall of around 200mm per hour ,whereas the drainage system can cope upto 150mm an hour. The northern part of the network which started functioning during 1876 has been designed with a rainfall of 1/4th inch per hour (150 mm per day) with 100% run off and the southern part (Suburban System) established in 1890 or so has been designed to a 1/6th inches rainfall per hour (100 mm per day). In the seventies, attempts were made to augment the capacity of the system to ½ inch rainfall per hour, but the target could not be achieved due to various technical and financial constraints. On an average, the city use to experience about 4 to 6 water logging in a year.
The scenario started to change as the climate change started to take its toll. The figure has shifted to 10-15 time in this decade alone as the monsoon rains have shown an eratic change with mid to heavy downpour even during the winter months of the city.
Among the cities facing growing flood-damage losses by 2050, Kolkata is projected to be among the top three with Mumbai being the second one from the Country.
According to the Organisation for Economic Cooperation and Development, if the current increase in greenhouse gas emissions continues, by 2070 , nearly half of city would it adversely affected by coastal flooding with many to most part going permanently under water.