Climatic conditions and processes change over space and time. Nearly 70 per cent of the earth’s surface is covered by oceans. Both land and oceans have different characteristics in terms of their heating and cooling capacities, resulting in differences in atmospheric pressure, temperature and relative humidity. In addition to the massive ice-sheets over the Arctic and the Antarctic, the warm and cold oceanic currents are also responsible for moderating the climate in different latitudes, as also the El Niño Southern Oscillation (ENSO).
However, land use changes through human activities have affected the natural weather systems, changing their characteristics as well as the rate of change. Changes in weather systems over long periods, whether due to natural or anthropogenic causes, are usually termed as climate change. Generally speaking, climate is a long term phenomenon, measured over a period of at least 30 years, that describes the average weather conditions and processes in a certain region in terms of pressure, temperature, precipitation (including rain, snow and hail-storms), relative humidity, wind speed and direction. Environmental studies related to climate, focus on air composition including greenhouse gases, suspended particulate matter, impacts of sunlight and cosmic rays and the ozone hole. While a meteorologist or climatologist carries out such studies for periods varying from a few years/decades to centuries over which scientific observations and instrumental data are often directly available; geologists and paleoclimatologists study climate changes over longer periods of time, that is, in terms of centuries and millennia, by going through the earth’s historical records, particularly the sedimentary and biotic deposits.
However, a common man’s concerns about atmospheric conditions and processes relate to short-term weather changes over a daily, weekly or seasonal basis. It primarily pertains to their dependency on natural weather for day to day activities like livelihood, agriculture, fresh water resources, and more. Extreme weather conditions in the form of extreme heat or cold waves, urban heat islands, high intensity or long duration heavy to very heavy rainfall with uneven distribution or delayed/advanced precipitation, acid rain, deep depressions resulting in high wind speeds/squalls, cyclones, rapid glacial melting and retreat brought by critical changes in weather conditions can turn these phenomena into hazards and disasters.
The Indian climate is dominated by a monsoon season that provides about 80 per cent of the annual rainfall, generally extending from June to September. The period between October and December is normally referred to as the north-east monsoon season, which affects parts of peninsular India. It is also known as the ‘post-monsoon season” or ‘retreating south-west monsoon season’. The north-east monsoon season is the major period of rainfall (40 to 60 per cent of the annual rainfall) in coastal Andhra Pradesh and Tamil Nadu. About 20 per cent of the annual rainfall in Kerala, Karnataka and Lakshadweep is also attributed to north-east monsoon. It is also noted that the maximum rainfall in this season occurs between late night and early morning spells of about 3-4 days, often being associated with a depression or cyclone.
The Intergovernmental Panel on Climate Change (IPCC) in its 5th Assessment report has discussed the emergent risk and key vulnerabilities due to climate change and proposed an approach to prevent, adapt and mitigate these risks. During the 3rd World Conference on Disaster Risk Reduction during March 14-18, 2015, UNISDR adopted the Sendai Framework for Disaster Risk Reduction (2015-2030) that also focused on ecosystem based disaster risk reduction and highlighted four priority actions with seven guiding principles. These priority actions were,
- Understanding disaster risk,
- Strengthening disaster risk governance to manage disaster risks,
- Investing in disaster risk reduction for resilience; and
- Enhancing disaster preparedness for effective response and to ‘build back better’ in recovery, rehabilitation and reconstruction.
Climatic conditions at Chennai
Chennai, the capital city of Tamil Nadu, is located in the south-eastern India on the shores of the Bay of Bengal. Together with 16 municipalities, 20 towns and 214 village panchayats, the metropolitan area of Chennai has about 9.19 million people. It is the biggest industrial and commercial centre in south India.
Due to it’s proximity to the sea, it has a low elevation coastal zone with the Adyar and Cooum rivers meandering through the city. These rivers are connected through the Buckingham canal. Besides the rivers, the city had about 650 small and big water bodies at one point of time. However, most of these lakes have disappeared or shrunk through the years. As a result, the number of existing lakes in Chennai stands at less than 30. The water courses of Chennai fall under the jurisdiction of Water Resources Division (WRD) of the Public Works Department (PWD).
Being close to the equator, Chennai has a hot and humid climate. It receives most (about 50 per cent) of its annual precipitation in October and November during the north-east Monsoon. The city has inadequate provisions for storm water runoff with only 855 km storm water drains against 2,847 km of urban roads, resulting in frequent flooding after even a marginally heavy rainfall. Most of its drains are clogged with silt, garbage and plastics resulting in a much lower actual carrying capacity than the expected discharge.
Chronology of recent weather events, impact and response
A depression over the southwest Bay of Bengal on the morning of November 8, 2015 intensified into a cyclone, ‘Rovan’ and on November 10, it crossed the northern part of the Tamil Nadu coast between Puducherry and Cuddalore. Heavy to very heavy rainfall resulted over many parts of Tamil Nadu, Andhra Pradesh and Karnataka, with some parts of Tamil Nadu reporting as much as 550 mm of rainfall between November 9 and 16.
On November 23, 2015, another spell of heavy rainfall caused fresh floods in the coastal districts of Tamil Nadu, Andhra Pradesh and Puducherry. Neyveli received 450 mm of rainfall between 8:30 am and 5:30 pm, causing water to pool. On November 28-29, another system developed and reached Tamil Nadu on November 30, bringing additional rain and flooding. Tambaram saw 490 mm of rain in 24 hours on December 1, 2015. According to data from IMD, Chennai received 1,522.7 mm of rain between December 1 and 4 as against a normal of 662.6 mm (130 per cent excess), Cuddalore 1,041.5 mm against a normal of 550.1 mm (89 per cent excess), Kancheepuram 1,681.4 mm against a normal of 535.1 mm (214 per cent excess), Thiruvallur 1, 414 mm against a normal of 496.9 mm (185 per cent excess), and Puducherry 1,406.1 mm against a normal of 673.5 mm (109 per cent excess). The rains led to flooding across the entire stretch from Chennai to Cuddalore. Stricken residents from Chennai, Kancheepuram and Thiruvallur districts attempted to flee their homes to safer places, with little success. Chennai airport had to be closed down, and re-opened only on December 5, 2015.
Damages have been estimated at over INR 50,000 crore, with more than 450 deaths in Tamil Nadu, 81 deaths in Andhra Pradesh and two deaths in the union territory of Puducherry. An overnight discharge from Chembarambakkam reservoir into the Adyar river became a watery grave for people who were trapped. A power breakdown during the floods killed 14 patients at a private hospital. The Hindu, for the first time in its history, could not publish a print edition on December 2, 2015, Chennai was officially declared a disaster area and the Coast Guard, the army, navy and air force were pressed into action for rescue. A relief package of INR 1,940 crore was announced by the Prime Minister even as relief camps were set up in Chennai, Kancheepuram and Thiruvallur. Insurance companies anticipate claims worth at least INR 500 crore, with motor insurance accounting for the bulk of the claims.
Inevitability of this preventable disaster
The Disaster Management Act 2005, envisages preparation and implementation of disaster management plans by the authorities at the district, state and national levels to ensure the safety of life, economy and the environment. As per IMD records, rains were expected in Chennai between October and December. The rains arrived on time. However, the unregulated and unscientific development over marshlands, lakes and ponds has played havoc to the natural drainage system which has either disappeared or reduced in capacity. Hence, more run-off is expected after rains with dysfunctional or insufficient drainage systems to carry water.
Further, the Chembarambakkam reservoir level was rising due to continuous rains in November. The standard operating procedures for maintaining the level of water in the reservoirs require systematic release of water from the sluice gates if the expected rainwater is likely to cross the critical threshold that can threaten the safety of the dam. On December 1-2, it had reached its threshold levels and was forced to release the excess water. In the wake of predictions of heavy to very heavy rainfall in Chennai by different agencies the Chembarambakkam reservoir could have systematically released water into the outskirts of the city so that the lake could bear the load of the heavy rains during subsequent days. Similarly tanks along the Adyar river could have also released some water prior to the heavy rains so that runoff could be diverted and accommodated in them.
The last decade has seen Chennai embrace development through the building of malls, bus terminals, mass rapid transit system, as also infotech, automobile and telecom complexes, most of which are on marshlands, ponds, lakes and drainage channels. This unregulated, haphazard, unscientific development left the city vulnerable and exposed to the wrath of nature. In short, it was a disaster waiting to happen, although preventable.