Hyderabad: As severe cyclonic storm Michaung hurtles down India's eastern coast, its impact is exacerbated by a combination of factors, including climate change, El Nino, and the Indian Ocean Dipole (IOD), Climate Trends, a research-based consulting and capacity building initiative, said on Tuesday.
Rising sea surface temperatures due to climate change extend heavy rainfall areas around the cyclone centre, increasing the risk of flooding in regions like North Tamil Nadu and South Andhra Pradesh.
El Nino, characterised by elevated equatorial sea surface temperatures, has surpassed 2°C for the first time since 2016. This phenomenon, intensified by global warming, contributes to the rapid intensification of cyclones. The unusual warmth in the Indian Ocean, coupled with the positive phases of IOD and Madden-Julian Oscillation (MJO), creates favourable conditions for cyclonic genesis.
The impact of climate change on cyclones is evident in the increased frequency and intensity, with warming oceans acting as energy sources. In the past 40 years, Andhra Pradesh has faced storms, cyclones, or heavy rains and floods almost every year, highlighting the region's vulnerability.
The trio of El Nino, IOD and MJO
El Nino, since the very beginning, has been in the news for its rapid intensification. Equatorial sea surface temperatures (SSTs) are above average across the central and eastern Pacific Ocean. Nino 3.4, the representative of ONI (Oceanic Nino Index), has crossed 2°C for the first time since February 2016, after the super El Nino of 2015. Chennai recorded 292 mm of rain on December 2, 2015 (An all-time high record).
El Niño is characterised by a positive ONI greater than or equal to +0.5oC. However, these ONI thresholds must be exceeded for at least five consecutive overlapping 3-month seasons.
El Niños usually peak around Christmas in December, a reason why they derive their name from the Spanish term for ‘little boy’. As oceans absorb more than 93% of the additional heat from global warming, El Niños are also getting stronger. They are not little boys anymore but monsters of the sea.
Changes in ocean-cyclone interactions have emerged in recent decades in response to Indian Ocean warming and are to be closely monitored with improved observations since future climate projections demonstrate continued warming of the Indian Ocean at a rapid pace along with an increase in the intensity of cyclones in this basin,” said Dr Roxy Mathew Koll, Climate Scientist at the Indian Institute of Tropical Meteorology.
Meanwhile, other two important oceanic phenomena, the Indian Ocean Dipole and Madden-Julian Oscillation, both associated with positive rainfall over Indian landmass, were in favourable zones. These, along with anomalous high sea surface temperatures, provided conducive dynamic and thermodynamic conditions for the genesis.
How global warming is changing the dynamics of cyclones for India?
The dynamics of cyclones in the North Indian Ocean are changing due to global warming. The large natural variability in a relatively short observational period makes it difficult to determine what percentage of the observed tropical cyclone activity changes can be attributed to ocean warming due to forcing by greenhouse gases.
It is worth noting that the impact of SST warming on cyclone activity is not only related to the magnitude of Sea Surface Temperatures (SST) change but also associated with the SST change pattern.
Role of SST in the intensification of cyclones: Recent observations indicate that cyclones in the north Indian Ocean are now exhibiting rapid intensification, intensifying by more than 50 knots in just 24 hours, in response to SSTs much higher than 30°C, prominently due to the rapid warming in the region. From 2000 onwards, the frequency of cyclones undergoing rapid intensification in the north Indian Ocean has increased.
The percentage of cyclones undergoing rapid intensification in the north Indian Ocean is higher (38%) than the cyclones in the northwest Pacific Ocean, where this rate is 22%. Due to the eastward shift of the cyclogenesis location in the Bay of Bengal, the cyclones are now travelling for a long time over the ocean and drawing more of the thermal energy released from the warm ocean waters, thereby enhancing the chances of developing into a very severe cyclone with intensity greater than 65 knots.
Ocean heat content, in addition to sea surface temperatures, influences cyclone intensity, especially for slow-moving cyclones. High ocean heat content sustains or intensifies cyclones by providing a continuous supply of heat fluxes to the atmosphere.
Cyclone Michuang, as the sixth storm of the year in the Indian Seas, exemplifies the changing landscape of post-monsoon cyclone patterns. December, the peak month of the post-monsoon cyclone season, typically sees cyclones heading towards Tamil Nadu and South Andhra Pradesh.
Loss and Damage from Cyclones on the East Coast of India
The Bay of Bengal witnesses more cyclones than the Arabian Sea due to favourable geographical and atmospheric conditions. Intense tropical cyclones possess destructive characteristics attributable to their mighty surface-level winds, extensive precipitation, and the resulting storm surge. Consequently, they can inflict significant harm upon agriculture, properties, and livelihoods, resulting in substantial economic losses.
The Bay of Bengal hosts more cyclones than the Arabian Sea on account of favourable geographical and atmospheric conditions. Cyclone Fani in 2019 caused an estimated economic loss amounting to INR 12,000 crores (US$1.6 billion) and damaged more than five hundred thousand houses within the coastal districts of Orissa. Cyclone Phailin in 2013 caused an approximate economic loss of INR 89,020 million (US $1.16 billion). It has been estimated that financial loss was nearly INR 8000 crores (US$1.1 billion) during the Odisha cyclone in 1999.
Cyclone Amphan was yet another powerful cyclone that tore through West Bengal, causing damage of 1 trillion rupees ($13 billion) to infrastructure and crops.
As Andhra Pradesh gears up for Cyclone Michuang, let us look at the history of cyclonic storms ravaging the southern coastal state. As per IMD, altogether, 184 cyclones of all categories, including depressions, crossed the coast from 1891 to 2019. The state is at risk of at least one cyclone each year on an average and maximum during October and November. Cyclones with moderate to severe intensity occur every two to three years, which results in huge damage to the state.
According to the state government, 2.9 million people are vulnerable to cyclones, as 3.3 million people are located within 5 km of the coastline. Since 1975, the state has faced more than 60 cyclones. In the past 40 years, there may not have been a single year in which the state did not experience either a storm, a cyclone, or heavy rains and floods.
As Cyclone Michuang approaches Andhra Pradesh, the history of cyclonic storms in the state highlights the need for robust preparedness and resilient infrastructure. With millions of people vulnerable to cyclones along the coastline, it is crucial to understand and address the evolving dynamics of cyclones driven by climate change, El Nino, and other oceanic phenomena. This understanding is essential for effective cyclone impact assessment, management, and the development of cyclone-resilient societies..
More on our 'Cyclone Michuang' coverage-
- Cyclone 'Michaung' likely to bring light to moderate rain in south Bengal: Met
- Cyclone Michaung: Rains pound Chennai; normal life disrupted; airport closed till 11 PM
- Cyclone 'Michuang': Heavy rain lashes parts of AP
- Cyclone Michaung: Tamil Nadu govt announces public holiday on December 5
- Respite for Chennai residents as IMD forecasts light rainfall in city after cyclone Michaung
- Cyclone Michaung landfall: Heavy rains pound Andhra as storm makes landfall; death toll rises in Chennai to 12
