WHY BIGGER STORMS ARE BREWING IN THE BAY

WHY BIGGER STORMS ARE BREWING IN THE BAY

Warming Of Oceans Triggered By Climate Change Rapidly Intensifying Cyclones

U.Tejonmayam@timesgroup.com

23.12.2020

When very severe cyclonic storm Nivar made landfall last month, meteorologists and authorities heaved a sigh of relief, as the storm was not as intense as anticipated. But climate scientists observed that it left a recurrent pattern which could lead to something more sinister. The weather system moved two stages up from depression to deep depression and later into a cyclonic storm in about 24 hours. Scientists term this development rapid intensification, driven by climate change and ocean warming. This trend can be deadly as it gives very little time for authorities to prepare for the worst.

Roxy Mathew Koll, climate scientist, Indian Institute of Tropical Meteorology, Pune, (IITM), said researchers have observed rapid intensification of cyclones in recent years, such as cyclones Amphan and Ockhi, which strengthened within 24 hours. And with global warming not slowing, there could be more cyclones rapidly intensifying in the future. A cyclone has rapidly intensified if wind speeds increase by 55kmph in 24 hours.

“These storms intensify faster than what we expect or the models forecast, so we have less time to be prepared for it. Ockhi didn’t give us the time to respond in terms of disaster management,” Koll said. “Ocean warming may not stop and all climate models show that Indian Ocean is going to warm at the same rate or more in the coming years. There are high chances of rapid intensification of cyclones in future,” he said.

As cyclones draw energy from warm waters, Koll said rapid warming of Indian Ocean in recent decades due to climate change is making the region conducive to cyclones and rapid intensification. Studies have shown that Indian Ocean has experienced rapid warming with an average rise of 1ºC in sea surface temperature during 1951-2015 when the global sea surface temperature warmed about 0.7 ºC.

Bay of Bengal is already in the warm pool region with sea surface temperatures around 28-29 ºC and at times touching 30 ºC. In May 2020, a few days before Amphan, data buoys in north Bay of Bengal measured record high surface temperatures between 32-34 ºC.

“A warm ocean is like a heat engine for these cyclones.

As soon as they make landfall, they lose their source of energy and with friction, they die. When we have warmer than usual waters, it keeps feeding that heat for the cyclones to intensify faster,” Koll said.

While the Bay of Bengal may have seen changes in the intensity of storms, Arabian Sea, cooler than the Bay, is brewing more number of cyclones because parts of the sea are getting warmer. Its western parts are getting as warm as Bay of Bengal.

Cyclones formed par- ticularly in November-end or December, have more chances of hitting Tamil Nadu coast due to the movement of equatorial trough or a belt of low pressure from near the Bengal coast to closer to the equator.

“The track of cyclones can be everywhere during the northeast monsoon. As the equatorial trough makes its southward journey, storms could move towards Tamil Nadu, AP, Odisha, Bengal, Bangladesh or Myanmar during October. But when the northeast monsoon advances, systems form in lower latitudes of the east coast which means they could move towards south AP or TN,” said Y E A Raj, former deputy director general, IMD.

Researchers said incorporating data on ocean sub-surface temperatures in the existing models and strengthening the existing ocean observation systems across the Indian Ocean region could help forecast rapid intensification.

M Rajeevan, secretary, ministry of earth sciences, said the present models occasionally pick up rapid intensification as they are run only with data on atmospheric conditions. Forecasting rapid intensification of cyclones requires incorporating data on ocean conditions into the models. “We now have a regional coupled model called Hurricane Weather Research and Forecasting, which uses both atmospheric and ocean parameters, developed with the help of the US. It is operational in IMD. But doing a detailed analysis on rapid intensification and to check if the models are picking it up may take some time. IMD is already on the job,” he said.