The North Indian ocean basin is churning stronger and slow-moving cyclones over the past two decades and the abnormal warming of oceans remains a concern for the Indian subcontinent and its disaster preparedness for extreme weather events, finds an analysis by Chennai Rains, an independent weather blogging site.
The rapidly-warming Indo Pacific Warm Pool (IPWP), which is the tropical ocean region located in the western Pacific ocean and the eastern Indian ocean, is a dominant factor influencing weather over Asia and the Indian subcontinent through increasing sea surface temperature over the North Indian ocean basin. IPWP is warming up faster than any other ocean body globally.
K.Srikanth, weather blogger with Chennai Rains (Chennaiyil Oru Mazhaikalam), said the number of intense cyclonic storms, be it very severe or extremely severe cyclones, has increased particularly since 2003 in the North Indian ocean comprising Arabian Sea and Bay of Bengal. The warm oceans are not only making cyclones stronger and slow moving but they also stay longer as intense weather systems.
This trend can potentially alter monsoon dynamics and disturb rainfall pattern or cause longer dry periods. It could bring recurring floods and prove a challenge for disaster management. For instance, cyclone Biparjoy spent nearly 10 days as a powerful tropical cyclone last year. Cyclone Kyarr remained strong for nearly 111 hours. The Arabian Sea has witnessed six times’ increase in the lifespan of cyclones as strong cyclones in the past 20 years compared to previous decades, he said.
The number of severe cyclonic storms in both the Arabian Sea and Bay of Bengal has increased to 16 in the past two decades since 2004 compared to 10 between 1984-2003. Similarly, extremely severe cyclonic storms in North Indian ocean rose to 17 between 2004-2023 compared to 11 in the previous decades since 1984. The analysis was based on the data from various agencies, including Regional Specialised Meteorological Centre, IMD; U.S.weather agency- National Oceanic Atmospheric Administration and European Centre for Medium-range Weather Forecasts.
The average annual sea temperature over IPWP and tropical Indian ocean is now 28.5 degree Celsius and sea temperature around south peninsular coast is around 27-28 degree Celsius. With a closed basin, it would take longer time for the ocean to cool.
While 2023 was the warmest year since global records started in 1850, similar trends of warmer surface sea temperature may continue irrespective of other global weather parameters like El Nino and La Nina. Carbon footprints and global warming are major influencers, and the impact of warm oceans would last for another five decades, said Mr.Srikanth.
With IPWP to progressively getting warmer, southern peninsular region with long coastline too remain vulnerable to more intense cyclones. Creating hazard maps and flooding zones and response plans would be of help, he added.
