Study: Intensity of severe cyclonic storms increasing in North Indian Ocean region

New Delhi: The intensity of severe cyclonic storms in the North Indian Ocean region has shown an increasing trend in the past four decades, according to a recent study by Indian scientists.

The increasing intensity of severe cyclonic storms with major socioeconomic implications was due to atmospheric parameters like higher relative humidity, especially at mid-atmospheric level, weak vertical wind shear as well as warm sea surface temperature (SST).

This indicates the role of global warming in bringing about this increasing trend, the study suggests.

A team of scientists, including Jiya Albert, Athira Krishnan, and Prasad K Bhaskaran from the Department of Ocean Engineering and Naval Architecture, IIT Kharagpur, jointly with K S Singh, Centre for Disaster Mitigation and Management, VIT University, Vellore, studied the role and influence of critical atmospheric parameters in large-scale environmental flow and El Nino-Southern Oscillation (ENSO) on tropical cyclone activity in the North Indian Ocean.

They were supported by the Department of Science and Technology (DST) under the Climate Change Programme (CCP).

In particular, the tropical cyclones that formed during the pre-monsoon season exhibited an increasing trend. In the recent decade (2000 onwards), the trend was found to be quite substantial in both Bay of Bengal and the Arabian Sea basins.

Findings from the study indicated 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 responsible for the increased tropical cyclone activity in the North Indian Ocean.

It was found that RH, RV, VWS are distinct during pre-monsoon seasons of La Nina, and that favours the genesis of severe cyclone formation over this region.

Environmental variables such as SST, wind streamlines, vertical velocity, and specific humidity exhibited comparable contributions towards cyclogenesis during both El Nino and La Nina phases.

Investigation of the role of additional parameters such as water vapour and zonal sea-level pressure gradients revealed the possible linkage of La Nina years on increased severity of tropical cyclones.

The study reported an increased amount of water vapour content in the troposphere, and during the past 38 years at 1.93 times as compared to the base year 1979.

During the past two decades (2000-2020), the La Nina years experienced almost double the number of intense cyclones compared to the El Nino years.