From bad to worse: How climate change fuels destructive power of Cyclone Mocha?

This year, the most severe cyclone of this season is hitting our land. The extremely severe cyclonic storm 'Mocha' has moved approximately 8 km in the last 8 hours and is moving in a north-northeast direction with an hourly velocity. It is located over the east-central Bay of Bengal, about 550 km northwest of Port Blair, 700 km from Cox's Bazar (Bangladesh) on May 13 and 650 km southwest in the direction of Sittwe (Myanmar). The storm is likely to intensify into an extremely severe cyclonic storm around the afternoon of May 14.

The India Meteorological Department (IMD) has stated that the wind speed in Cyclone Mocha is likely to exceed 175 km per hour. Its impact may result in rain over most of the Andaman and Nicobar Islands on May 13. Heavy rain is also possible today in many places in northeastern Mizoram and Tripura. Similarly, in Manipur, Nagaland and southern Assam, heavy rain is possible in several places on May 14 due to its impact.

Mocha's ravages in the Northeast

Due to Cyclone 'Mocha', there is a possibility of wind speeds ranging from 50-60 km/h up to 70 km/h in the Andaman Islands until the morning of May 13. According to the IMD, there is a possibility of wind speed ranging from 50-60 km/h up to 70 km/h in Tripura, Mizoram and southern Manipur due to 'Mocha' on May 14.

The sea over the Andaman Sea, especially the northern Andaman Sea and the Bay of Bengal, could be very rough today. Similarly, the sea is rough in the eastern Bay of Bengal, and these conditions will continue until the morning of May 14. After that, there will be a gradual improvement.

Cyclone Mocha and Climate Change

Weather conditions are currently very favourable for the intensification of the first cyclonic storm of this season, Cyclone Mocha. According to the country's nodal agency, the India Meteorological Department, there is a possibility that by the afternoon of May 14, 2023, Cyclone Mocha will cross the coasts of southeastern Bangladesh and northern Myanmar as a very severe cyclonic storm, between Cox's Bazar, Bangladesh and Kyaukpyu, Burma.

According to a study on the changing state of tropical cyclones over the northern Indian Ocean, there has been a decrease in the speed of cyclones in the Arabian Sea. Cyclones are now moving slowly. Increased cyclonic activity in the Arabian Sea is strongly related to increased moisture availability due to rising sea temperatures and global warming.

Understanding this situation, Dr Roxy Mathew Koll, climate scientist and lead author from the Indian Institute of Tropical Meteorology, says: "The state of the weather over the ocean is very helpful for the intensity of this system. While cyclogenesis has decreased in In the Bay of Bengal, the intensity of cyclones has multiplied several times. Cyclones can now maintain their destructive energy for many days. Cyclone Amphan was an example of this trend, which continued as a powerful cyclone over land, causing widespread devastation. As long as the oceans continue to warm and the winds remain favourable, cyclones will maintain their intensity for longer periods."

Dr Col further explains: "The Bay of Bengal has been particularly affected by global warming in recent decades. The temperature in the Bay of Bengal remains between 30 and 32 degrees Celsius. These high temperatures play a huge role in the intensity of cyclonic storms because they transmit more convection. Such intense intensity has recently occurred repeatedly in both the Arabian Sea and the Bay of Bengal."

Effects of climate change on cyclogenesis

Tropical cyclones (TC) are one of the most destructive natural disasters, causing the loss of more than half a million lives worldwide in the last five decades. More than 75% of all TCs in the last 300 years that have resulted in the deaths of 5,000 or more people have occurred in the North Indian Ocean (NIO).

The risks posed by increased cyclonic activity due to human-induced climate change have been well established. The Indian Ocean area, which includes the Arabian Sea (AS) and the Bay of Bengal (BoB), is of particular concern due to the high population density along its coastlines.

"Sea surface temperature is rising. The mechanism behind cyclone formation remains the same, but weather conditions are changing. In recent days, cyclones are becoming more intense at a rapid rate. The reason Behind this is not only rising sea surface temperature (SST), but also rising ocean heat content (OHC)" said Dr. M. M. Ali, Andhra Pradesh State Disaster Management Authority Meteorologist and Oceanographer and Emeritus Scientist and Group Director - Atmospheric, ISRO (Indian Space Research Organization).

He further added, "Previously, it took 2-3 days for a system to become a tropical cyclone, but today it changes to a depression to a cyclonic storm in just one day. The atmosphere not only interacts with the SST, but also with the entire ocean. Research shows that the OHC is changing due to climate change,"

Greenhouse gases causing climate change

According to the IPCC, the long-term presence of greenhouse gases in the environment is primarily causing climate change, which has increased the radiative forcing of the climate system.

The Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) highlights impacts on the ocean and cryosphere. One consequence is an energetic imbalance at the top of the environment, about 92% of which is absorbed by the ocean as it continues to warm. Leading indicators of climate change include global average surface temperature, sea level, and rising ocean heat content (OHC).

In the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), there is an estimate of an increase in both sea surface temperature (SST) and ocean heat content (OHC) in the future. There will be a warmer, wetter world over the oceans, providing more energy for evaporation, leading to more TC activity and more precipitation.

Intense hurricanes may increase

The likelihood of fewer but more intense storms (i.e. Category 4 or 5 hurricanes) may increase, in part due to changes in atmospheric stability, with a few major storms replacing several smaller storms in terms of impact in the ocean.

"The barrier layer is a layer between the upper and lower layers of the ocean. As the OHC increases, this layer becomes stronger and therefore heat cannot reach the lower layer of the ocean. We follow the OHC and track where it is higher we have seen this in the Arabian Sea and the Bay of Bengal where cyclones usually weaken due to wind and low humidity near the coast as they remain near the coast however "These days, even near-coastal cyclones maintain their strength. This is a serious danger to both sides of the Indian coast," Dr. Ali said.

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