CHENNAI: The Sirkazhi weather station in Mayiladuthurai has recorded its all-time highest 24-hour rainfall of 44 cm. Six stations recorded extreme rains in excess of 20 cm, 16 clocked heavy to very heavy rains, and 108 registered heavy rains. This is among the heaviest rainfall spells during the northeast monsoon in recent years.
What is causing these cloudburst-like events? Experts say warming of Bay of Bengal sea surface temperature and favourable oceanic conditions are fuelling weather systems with more energy and moisture and increasing extreme rainfall events.
Mahesh Palawat, chief meteorologist of SkyMet Weather Services Pvt Ltd, said: “The sea surface temperatures are above average. The threshold value is 26.50C, beyond which conditions are very favourable for cyclogenesis or rapid intensification of any weather system. The current value is 29-300C. The well-marked low-pressure area, which caused cloudburst-like rains in Mayiladuthurai and Cuddalore, drew significantly higher moisture than usual and dumped everything in the coastal districts of delta.”
He said had the low pressure area formed in the southeast Bay of Bengal and with a travel time of 4-5 days, it would have intensified into depression or even cyclone. “A new low-pressure area is likely to form near Andaman around November 17. There are high chances of it intensifying.”
P Senthamarai Kannan, director, Area Cyclone Warning Centre at the Regional Meteorological Centre, refused to call Sirkali rainfall event a cloudburst. “Yes, extreme rains of 44 cm occurred, but that happened over a period of 24 hours in different spells. Cloudburst is when rainfall happens suddenly in a few hours. Here, there is a weather system locked close to the coast and pushing moisture inland as it tries to cross. Such rain was witnessed in the past.”
C Balaji, TT Narendran chair professor, Department of Mechanical Engineering, IIT Madras, said: “We plan to conduct a detailed study on this. We were tracking the movement of the system and would see a large mass of clouds moving into Mayiladuthurai and Cuddalore belt. At times, rainfall was as intense as 100 mm per hour. One broad conclusion from the climate change point of view is that the number of rainy days are decreasing. For authorities, it poses a great challenge.”
Although Chennai escaped this time with moderate to heavy rains, it is among India’s most ‘climate’ vulnerable districts. A district-level vulnerability assessment by the Council on Energy, Environment and Water ranked Chennai seventh among districts prone to extreme floods and cyclones.