‘Rise in temperatures could lead to more pre-rain cyclonic storms’
With the formation of Cyclone Amphan in the Bay of Bengal, followed by the likely formation of Cyclone Nisarga in Arabian Sea within two weeks, scientists have warned about the possibility of more pre-monsoon cyclonic storms in coming years owing to warmer ocean temperatures.
Dr Roxy Mathew Koll, senior scientist, Indian Institute of Tropical Meteorology (IITM), said, “We are aware that postmonsoon cyclones have increased, but climate models and projections are indicating the likelihood of more cyclones before the onset of the southwest monsoon in the Arabian Sea.”
Sea surface temperatures in the Arabian Sea were plotted on a map, showing the difference between long-term average temperatures and temperatures on May 30, as the weather system that is yet to intensify into Cyclone Nisarga developed.
“While the temperatures in the Bay of Bengal were between 30 and 33 degrees Celsius prior to Amphan, surface temperatures over the Arabian Sea recorded 30-32 degrees Celsius prior to the depression which is now evolving as Cyclone Nisarga. Such high temperatures aid rapid intensification of these cyclonic systems, which many weather models fail to capture,” Koll said.
According to IITM, sea surface temperatures between 24 and 26 degrees Celsius are normal. The India Meteorological Department (IMD), however, said that higher ocean temperatures were not a factor for the intensification of Cyclone Nisarga.
“During Amphan, warmer oceans allowed the system to reach a super cyclone status but not in this case so far,” said Mrutyunjay Mohapatra, director general, IMD.
Warmer ocean temperatures are not the only parameter for rapid intensification of cyclones, said Mohapatra. “We need to consider other parameters, such as relative humidity in middle troposphere and instability in the atmosphere, allowing moist air to form aiding cloud formation through the help of convection. There are also other parameters to be considered. However, the frequency of cyclones has been abnormally high in the Arabian Sea from a year and it is a fact that this zone is witnessing an increase in cyclones,” said Mohapatra.
‘CITY AT HIGHEST RISK’ Dr Anjal Prakash, research director and adjunct associate professor, Bharti Institute of Public Policy, Indian School of Business, Hyderabad Campus, highlighted concerns raised by the Madhav Chitale committee after the July 2005 deluge.
“The most-affected city is Mumbai. The committee [Madhav Chitale committee] said inadequate drainage system, rapid developments, loss of ponds that hold water, slum encroachments over the existing drainage systems, and reduction of coastal mangroves to be reasons behind flooding. These are the adaptation measures which Mumbai must focus on,” said Prakash.