A change in climatic patterns, the absence of seasonal rainstorms and a degraded environment have conspired to hold southern Bengal a hostage to heat

Streets in Kolkata are deserted in the afternoon because of an unprecedented heat wave in April. (Image by Sagarika Bose)

Streets in Kolkata are deserted in the afternoon because of an unprecedented heat wave in April. (Image by Sagarika Bose)

The weather seems to be catching up with the election heat in West Bengal. When Chief Minister Mamata Banerjee pitched for an earlier than scheduled assembly election in the state to evade the scorching sun of May, she could not have anticipated that the campaigning in April will be under the spell of an unprecedented heat wave.

The southern part of West Bengal that includes capital Kolkata has experienced a record rise of mercury in the first fortnight of April, an expert in the regional office of the India Meteorological Department (IMD) told indiaclimatedialogue.net. “We have never seen such high level of sustained heat, consistently 40 degree Celsius and around, during this period of year in a major part of south Bengal including Kolkata,” said G.C. Debnath, deputy director general of the Met department. The usual maximum temperature in south Bengal at this time of the year hovers between 35 and 38 degrees.

Many experts attribute this trend of increasing temperatures to the combined effect of climatic variability coupled with local degradation of the environment.

“From 7 to 16 April, the maximum temperatures in Bankura, Asansol, Birbhum and Kalaikunda have remained over 40 degree Celsius on all days and Bankura actually had a heat wave for about half of those days,” said Debnath. A heat wave is announced when the maximum temperature rises 4.5 degrees above the average maximum provided the figure touches 40 degrees.

Kolkata is no exception. In 2015, the mercury never touched 40 degrees but this year in the first fortnight of April itself, the benchmark was crossed on nearly half of the days, with the upper number reaching 41.3 degrees in Alipore observatory on April 11, highest figure for the month in the past decade.

“We have never seen a hotter first fortnight of April in Kolkata,” Debnath said. On an average, the maximum temperature remained four degrees above normal, official data show. A heat wave was declared Between April 10 and 12 and the schools are shut due to the excessive heat.

The hot spell is set to continue as the IMD has projected that the temperature would hover around 40 degrees Celsius in the next few days.

Burning Bengal

Date Maximum Temperature (degrees Celsius)
Bankura Kolkata Kalaikunda Birbhum Asansol
April 7 45 40.1 42.1 41.9 42.2
April 8 43.2 37.6 40.5 45 41.1
April 9 44.2 38.6 41.8 42 41.9
April 10 45.1 40.5 42.1 42.6 43
April 11 45.6 41.3 42.9 43.6 43.6
April 12 43.2 40.6 42 41.8 41.3
April 13 43 39.6 41.8 40.7 40.6
April 14 43.6 40 42.5 41.5 41.3
April 15 44.5 40.3 43.4 41.9 42.6
April 16 46 35.1 40.8 43.5 44.1
April 17 42.8 38.2 43.8 37.2 39

Source: India Meteorological Department

What has led to such high temperatures that are more often seen in the northern plains rather than in the Gangetic delta? “The reason for the sustained heat is the lack of development of a high pressure area close to West Bengal coast, which in turn hinders inflow of moisture from the sea. As a consequence, hot air from central and north India is entering into the city, turning it into a hot chamber,” explained Debnath.

Sutapa Choudhury, head of the atmospheric sciences department in Calcutta University, noted the changing climate and pointed out that the lack of norwesters, the evening storms that cool the land in late spring, is contributing to the trend. “There have been disturbances in the formation of norwesters so far in and around city,” said Choudhury.

“Moisture fuels the norwesters and helps in development of clouds. A lack of moisture is affecting the formation of norwesters so far,” said Debnath. The IMD expert said although normally April sees at least four norwesters, this year there has been none so far.

As a result, rainfall in Kolkata was 84% less than normal in March and April at 9.1 mm compared with the usual 58.7 mm.

Environmental experts say apart from the climatic factors, local degradation of the environment is also significantly contributing to the heat wave during the first half of April in southern Bengal.

Heat island

“The urban areas of south Bengal, particularly Kolkata, are becoming heat islands due to a combination of factors. Random felling of trees, rapid increase of vehicles on the roads and addition of a huge amount of carbon dioxide in the local atmosphere, and the filling up of water bodies and wetlands are the major contributors to the trend,” said environmentalist Somendra Mohon Ghosh. “Around two million vehicles ply within greater Kolkata daily, contributing minimum 10,000 tonnes of carbon dioxide at a rate of minimum five kg per car.” The emission of the noxious gas traps more heat.

Urban areas in West Bengal have been witnessing a rapid decline of both water bodies and greenery in the name of real estate development. While most international cities have 15% to 20% green cover, Kolkata lags with hardly 5% cover. A few other urban areas in the state have even less than that.

“Though there has not been any survey per se, but our experience is that lakhs of trees have been felled and thousands of water bodies have been filled up in last couple of decades within urban areas of West Bengal on the pretext of development and the government has mostly played the role of a mute observer if not a silent accomplice,” alleged environmentalist Naba Dutta, secretary of Sabuj Mancha, a platform of environmental organisations and individuals in state.

“In response to a public interest litigation filed by me, the anti-tree cutting act was passed in the state a few years back but it has largely remained on paper with the administration almost becoming a conduit for the real estate mafia, which is being protected by political powers,” environmental activist Subhas Datta said.

“The increase of heat has a multiplier effect. People are installing air conditioners that in turn are throwing more hot air and pushing up the mercury even more,” said a professor of environment science at Calcutta University who declined to be named.

Experts say that with increasing burgeoning level of construction, the urban heat islands in West Bengal are becoming hotter with every passing day. In its latest report, the Intergovernmental Panel on Climate Change has forecast that heat waves will be a major consequence of global warming.

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