Disaster Management

KMC’s land area is relatively flat and low-lying and its non-uniform slope generally trends away from the river towards the east and south-east. The area lies within the tidal reaches of the River Hooghly, was once a wetland, but now is the urbanised heart of KMA, a highly and densely populated area.

The city initially grew in a roughly north-south direction along a stretch of the River Bhagirathi, but later extended eastwards to encroach upon the back swamps and wetlands. Growth has been accentuated by high in-migration, with many of the incoming population having to live in low-income neighbourhoods across the city located on marginal land located on the floodplain and along the natural drain paths and drainage channels, narrowing them and effectively reducing their capacity. Inadequate drainage of storm water run-off increases the frequency and severity of localised flooding.

The climate of Kolkata is considered to be tropical wet and dry, with an annual mean temperature of 28.3ºC. Much of the rainfall is received from the south west monsoons during the months of June to September. In the last two decades the precipitation has been sporadic, with long dry spells, followed by heavy downpours towards the end of the monsoon season. This usually leads to flooding/ water logging in various parts of the city.

Several studies indicate that coastal urban areas, particularly mega cities located in low lying deltaic regions, are more prone to the risk of coastal flooding. Kolkata is currently ranked as the third most vulnerable city in the world from coastal flooding. The main impacts of these flood events, apart from damage to life and property is the deterioration in environmental health; a decrease in the wellbeing and living conditions for residents; and the impacts that flooding has on the livelihoods.

Finding from Studies

Summarised findings from climate variability and climate change studies indicate the following:

  1. Over the last 63 years instances of daily maximum temperature exceeding 40oC have increased; the highest maximum temperatures are in the pre monsoon season.
  2. Minimum/ maximum temperatures are projected to rise;
  3. Mean annual maximum temperature (31.2oC) is projected to increase by between 1.0-1.6oC by mid-century and by 1.7-3.3oC by end-century.
  4. Temperature increase will be more in winter.
  5. Excess rainfall once every five years; deficient rainfall once every 6 years;
  6. Positive trend in 1-day maximum rainfall (extreme events); extreme rainfall events are expected to increase.
  7. Mean annual precipitation is projected to change by between -2.8%-1.0% by mid-century and by between 1.6%-1.7% by the end of the century;
  8. Kolkata has experienced over 123 depressions/ cyclones in last 150 years. The number is likely to increase in the future.
  9. There has been noticeable land use change from green spaces to impervious surfaces around south/ south-eastern parts of the city.

From these studies, a number of key issues relevant to the preparation of a Disaster Management Plan for Kolkata were identified with these being indicated below.

  1. The eastern tidal creeks, as well as the River Hooghly, are susceptible to water level variations due to tidal actions. Extreme rainfall, due to tropical cyclonic activity/ depressions in the Bay of Bengal, results in excess runoff within the city. The increase in the paved surfaces and the limited carrying capacity of the creeks during high tides, results in localised flooding.
  2. The city’s topography has low-lying areas. These are easily inundated and require time for the water to drain away. Population increase and a capacity deficit at ward level have led to improper land use patterns and the spread of habitation into these low-lying areas.
  3. All the underground drains are combined sewers (sewer and storm water). There needs to be a separate arrangement for draining storm water in the event of a high precipitation.
  4. Most of the city drains are old and were designed to carry smaller volumes of effluent than they are currently required to do. Existing drainage capacities need to be augmented to match demand resulting from rapid population and urban growth. They are often heavily silted, reducing water retention and drainage capacities and increasing time for storm water drainage.
  5. The canals and rivers, which receive sewerage/ storm water, are in need of frequent desilting to avoid backwater thrust into the city drains.
  6. Most canals, channels and rivers are susceptible to water level variations that occur in the Bay of Bengal. Tidal water enters these during high tides/ storm surges. The coincidence of a heavy precipitation increases drainage problems. The existing system was based on a probable rainfall of 6mm/ hour; this is often exceeded.
  7. Kolkata’s slums are highly vulnerable to floods and cyclones due to use of poor construction material, weak social structure and their vulnerable locations. Some are located in highly vulnerable zones that were previously low-lying wetlands surrounded by vast water bodies into which sewage flows from the city. Squatter settlements on the banks of canals are not only vulnerable, but also spoil the ecological balance of the canals.

Vulnerability findings

  • Economically weaker groups reside in the most flood prone areas, often along the canals or in the floodplains.
  • Low-income groups (34% of respondents) are exposed to weeks of waterlogging due to lack of drainage facilities and sewerage backflow.
  • More than 25% of the residential buildings have their plinth below the road level.
  • Majority of the households in the study area reside in semi-pucca houses (around 74%).
  • 78% of high-income households have 2+ working members; it is only 10% among the lowest income category increasing economic vulnerability during natural disaster events.
  • The impact of flood/ waterlogging varies across the study wards; in Ward 143 on the fringe of the KMC area 60% had been affected, whilst in Ward 73, only 21 % had been affected.
  • Over 33% of the employed population in the study area live off a daily income source; these are most at risk of income loss, due to water logging disrupting their daily activities. 53% of those surveyed had lost man-days due to water logging with the loss of man-days ranging from 2-21 days annually.
  • Losing 21 working days results in an annual income loss of some INR 5250 per year. With minimum assets and resources and low to no savings, loss in income of daily wage earners increases their socio-economic vulnerability.

Given its location at the top of the Bay of Bengal, Kolkata has experienced similar events in the past, with the most recent event being in September 1978. On 28th of September the city witnessed rainfall amounting to 369.6 mm leading to several parts of the city being affected. The climate prognosis for West Bengal indicates that monthly average rainfall will be experienced in just a few weeks or days. This suggests the likelihood of extreme events of a similar magnitude to 1978, or greater, in the future. Heavy rainfall accompanied by cyclonic winds and storm may worsen the situation.

Potential Flood Risk in Kolkata based on Chennai’s Rainfall (December 2015)

In late November 2015, whilst this study was being conducted, Chennai experienced an extreme rainfall event (1 in 100 year event) resulting in more than 300 deaths and several hundred thousand people having to be evacuated from their homes. The water level in certain parts of the city was over nine meters, inundating houses and forcing many residents to take shelter on their rooftops. Given the extent of the impact, the state government had to seek the help of the National Disaster Rescue Force to assist them in the rescue and relief operations. The rainfall experienced was more than twice the normal rate. Several states and cities in India have witnessed similar extreme events over the last decade.