CHENNAI: Northern parts of Tamil Nadu including Chennai may experience heatwave like conditions for a week with day time temperatures expected to be 3-4 degrees above normal. On Tuesday afternoon, the mercury breached the 40 degree Celsius mark in the city for the first time this summer and the meteorological department predicts that it will soar further.
The sudden change in weather is attributed to super cyclonic storm Amphan, which has taken away all the moisture from the region. Besides, the westerlies are bringing dry land breeze from Rayalaseema and Telangana regions into north Tamil Nadu that may trigger a heatwave.
The mean day time temperature for the month of May in Chennai is 37.1 degrees Celsius. At 2.30 pm on Tuesday, the Chennai weather station in Nungambakkam recorded 40.2 degrees Celsius, which is 3.1 degrees above normal.
N Puviarasan, director, Area Cyclone Warning Centre of Regional Meteorological Centre, told The New Indian Express, "We will declare a heatwave when a station temperature records 4 degrees above normal. In Rayalaseema and Telangana, there would be a heatwave in a day or two with temperatures already touching 41-43 degrees in isolated pockets. The dry land breeze will blow into Chennai or its neighborhood."
Meanwhile, weather scientists say the warm Bay of Bengal may throw up more deadly cyclonic storms that rapidly intensify. Cyclone Amphan intensified from a category-1 cyclone to a category-5 cyclone in a short span of 18 hours.
Cyclones are fueled by available heat. Warming seas can make cyclones more powerful, by increasing the potential energy available to them, effectively increasing their power ceiling or speed limit. Higher sea-surface temperatures mean that cyclone wind speeds can increase.
Roxy Mathew Koll, a scientist at the Indian Institute of Tropical Meteorology and lead author of IPCC Oceans and Cryosphere, said: "Our research shows that high ocean temperatures are conducive for rapid intensification of cyclones in the north Indian Ocean. In the current case, the Bay of Bengal has been particularly warm. Some of the buoys in the Bay of Bengal registered maximum surface temperatures of 32-34 degrees Celsius consecutively for the first two weeks of May. These are record temperatures driven by climate change — we have never seen such high values until now."
Globally, ocean temperatures have increased as a result of climate change and there has been a global increase in the observed intensity of the strongest storms over recent decades. A study published in the US-based Proceedings of the National Academy of Sciences a couple of days ago projects an increase in the strongest storms by 8 per cent a decade.
Experts also believe there is a correlation between air pollution and cyclones. It is possible that reduction in air pollution in the region due to the COVID-19 lockdown may have influenced cyclone Amphan. Aerosols, from human-caused air pollution, can partly reduce the strength of cyclones in various ways. One factor is that aerosols reduce the amount of sunlight reaching the Earth’s surface, cooling it slightly.
Reductions in air pollution may have slightly increased sea surface temperatures in the Bay of Bengal, adding to the effect of climate change. In addition, aerosols can make clouds produce rain more easily, which limits the formation of cyclones. These factors suggest that reduction in air pollution would tend to increase cyclone strength.
Taking the argument further, V Vinoj, Assistant Professor, School of Earth, Ocean and Climate Sciences, Indian Institute of Technology, Bhubaneswar, said, "The reduced pollution levels have decreased aerosols that block sunlight, which in turn led to ocean surface warming. This may be the reason why Amphan has strengthened into a super cyclone, next only to the 1999 super cyclone. This will need to be investigated in the future."