Meteorologists rule out any direct linkage between the ongoing heavy rains in Chennai and adjoining areas with climate change, but they also aver that its contribution cannot be negated completely. A major consequence that worries most of them is the increased shelf life of low-pressure areas over land with disastrous consequences as witnessed in recent times.

They point to the rise in global temperatures which have increased the frequency of heavy rain events. The Indian Ocean is warming at a faster rate, with sea-surface temperatures (SST) soaring above average - 26.5 degrees celsius, the threshold value, past which the conditions turn very favourable for cyclogenesis or rapid intensification of any weather system.

Extended life of low’s over land

Rise in sea surface temperatures has led to stronger storm surge. Storm surge is an abnormal rise of water generated by a storm, over and above the astronomical tide. Extended shelf life of low-pressure area over land exacerbates the situation. This means the period of the weather system moving over land would increase the damage potential in direct proportion.

“Sea level in the North Indian Ocean rose at the rate of 1.06 mm-1.75 mm a year from 1874-2004 and 3.3 mm a year between 1993-2015. Unlike some oceans, most sea level rise here is is due to global warming,” according to Friederike Otto, Associate Director, Environmental Change Institute, University of Oxford.

Climate Trends, a strategic communications initiative on climate ambition and low carbon development pathways, quoted Otto as saying this while holding forth on the theme on the sidelines of launch of UN's Intergovernmental Panel on Climate Change report ‘Climate Change 2021: The Physical Science Basis’.

Coastal regions at risk

Swapna Panickal, Scientist, Indian Institute of Tropical Meteorology (IITM), Pune, says that the Indian Ocean region warming at a higher rate means the sea levels can also increase. Hence, the coastal regions will see sea level rise through the 21st century, and it will contribute to more frequent and severe flooding and erosion. Along with this, extreme sea level events previously witnessed once in hundred years could happen every year by the end of the century.

Mrutyunjay Mohapatra, Director-General, India Meteorological Department (IMD), says that climate change has led to an increase in SSTs that in turn has resulted in sea level rise by 10-15 per cent. Further, it is an established fact that global warming has increased the frequency of heavy rains, even associated with a low-pressure area.

Roxy Mathew Koll, climate scientist at the IITM, says that the Indian Ocean is getting warmer at a faster rate than any other ocean in the world due to greenhouse gases. Although rate of warming is more in Arabian Sea than Bay Bengal, the rise of a degree or two in oceanic temperatures can have large impact.

Threat for Tamil Nadu coast

“One crucial aspect of climate change for the East Coast including Tamil Nadu is that extreme weather and climate events are overlapping. The sea level is rising, so is the flood level due to storm surge and rain. These compound events are increasing now due to climate change. Often, they coincide with a high-tide pushing water several kilometres inland,” added Koll.

GP Sharma, President-Meteorology and Climate Change, Skymet Weather, said that the impact of rise of 1-2 degrees in the ocean temperatures is much more than compared to the increase in land temperatures. The relation between temperature and oceanic heat potential can be exponential.

Rise in SST means weather systems would be gaining more strength and moisture. This has also increased the shelf life of the weather systems, which then tends to travel inland for longer duration.

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