Intensity of severe cyclonic storms increased in past 4 decades, say scientists

  • Scientists pointed out that global warming has a role to play in bringing about the increasing trend
A man takes pictures as waves lash over onto a damaged shoreline during Cyclone Yaas. (AFP)
A man takes pictures as waves lash over onto a damaged shoreline during Cyclone Yaas. (AFP)
Published on Jul 29, 2021 04:16 PM IST
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Written by Shankhyaneel Sarkar | Edited by Avik Roy, Hindustan Times, New Delhi

Intensity of severe cyclonic storms in the North Indian Ocean region showed an increasing trend over the past four decades, the Union ministry of science and technology said in a statement on Thursday, attributing it to Indian scientists in a recent study.

The scientists expressed their concern over the impact of global warming due to climate change and its effect on extreme weather events like the increase in frequency and intensity of tropical cyclones formed over global ocean basins.

The scientists said that the cyclones are of significant risk and increase the vulnerability among communities living along the coastal regions. They said that atmospheric parameters like higher relative humidity, especially at mid-atmospheric level, weak vertical wind shear as well as warm sea surface temperature were the primary reasons for this disturbing development. Scientists pointed out that global warming has a role to play in bringing about this increasing trend.

Scientists Jiya Albert, Athira Krishnan, and Prasad K Bhaskaran from the department of ocean engineering and naval architecture, IIT Kharagpur, worked jointly with KS Singh Centre for Disaster Mitigation and Management, VIT University, Vellore on the study. They were supported by the Centre’s department of science and technology under the Climate Change Programme.

These scientists studied the role and influence of critical atmospheric parameters in large-scale environmental flow and El Niño–Southern Oscillation (ENSO) on tropical cyclone activity in the North Indian Ocean. The research showed correlation between a measure on destructive potential of tropical cyclones called Power Dissipation Index. The research published in the journal ‘Climate Dynamics’ recently showed that tropical cyclones that formed during the pre-monsoon season displayed an increasing trend. The trend in the post-2000 years was quite substantial in both Bay of Bengal and Arabian Sea basins.

The study said that strong mid-level relative humidity (RH), positive low-level relative vorticity (RV), weak vertical wind shear (VWS), warm sea surface temperature (SST), and suppressed outgoing longwave radiation (OLR) are factors responsible for increased tropical cyclone activity in the North Indian Ocean. During the research, the scientists found that RH, RV, VWS are distinct during pre-monsoon seasons of La Niña and it favours the genesis of severe cyclone formation over this region. Factors like sea surface temperature, wind streamlines, vertical velocity and specific humidity which are environmental, showed comparable contributions towards cyclogenesis during both El Niño and La Niña phases.

The scientists investigating the role of additional parameters such as water vapour and zonal sea level pressure found that increased severity of La Niña years is linked to tropical cyclones.

The scientists reported an increased amount of water vapour content in the troposphere and over the past 38 years at 1.93 times as compared to the base year 1979. Between 2000 and 2020 the La Niña years experienced double the number of intense cyclones compared to the El Niño years.

“During La Niña years, the positional shifts in average cyclogenesis of intense cyclones in Bay of Bengal are analogous with the observations for the western North Pacific Ocean basin. An increasing trend in the climatological distribution of water vapor content was also seen during these years, with peaks localised over the Andaman Sea and North China Sea regions in conjunction with the increased frequency of severe cyclones,” the release said.

The findings from the study are expected to increase advanced research in tropical cyclone activity for the North Indian Ocean region. It will also allow for a detailed investigation on the possible links and teleconnections with other climate indices over the North Indian Ocean.

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Sunday, October 24, 2021