Why higher prediction of cyclone depth, heavy rainfall is required

Heavy downpour: In Puducherry, Cyclone Fengal dumped 48.4 cm of rainfall in 24 hours.
| Photograph Credit score: ANI

Tropical cyclones rank among the many most devastating pure phenomena, with the potential to inflict important destruction and lack of life. Whereas the North Indian Ocean basin experiences fewer cyclones in comparison with different areas, it stays extremely prone to their impacts as a result of densely populated coastal areas. This vulnerability was tragically highlighted by the Bhola cyclone of 1970, the deadliest tropical cyclone on file. Observational proof signifies shifts within the patterns, depth, and frequency of tropical cyclones, underscoring the necessity for adaptive measures in susceptible areas.

Climatologically, the Bay of Bengal experiences a better frequency of tropical cyclones in contrast with the Arabian Sea. Lately, there was a 52% enhance within the frequency of cyclonic storms within the Arabian Sea, alongside a threefold rise within the length of very extreme cyclonic storms. There’s a larger chance of cyclonic storms intensifying into extreme cyclonic storms. Within the satellite tv for pc period, the gathered cyclone power over the North Indian Ocean has proven an growing development. These tendencies are pushed by environmental elements reminiscent of rising ocean warmth content material and reducing vertical wind shear.

In future local weather change situations, anthropogenic local weather change is more likely to gasoline extra highly effective tropical cyclones. Moreover, the tropical cyclone precipitation charges are projected to rise, pushed by elevated atmospheric moisture related to world warming. Ocean basins might also expertise a better frequency of speedy intensification occasions, a poleward migration of the latitude of most depth, and a slowing of the ahead movement of tropical cyclones.

The post-monsoon season of 2024 (October-December) was notably energetic, with as many as eight low-pressure techniques forming over the North Indian Ocean. Amongst these, 4 intensified into depressions, and two additional developed into cyclonic storms: Dana in October and Fengal in November. This heightened exercise was attributed to above-normal sea floor temperatures and beneficial atmospheric circulation together with low vertical wind shear. Cyclone Dana considerably impacted Odisha and West Bengal, inflicting in depth harm. Nonetheless, exact forecasts and efficient catastrophe mitigation measures minimised the lack of human lives.

Cyclone Fengal created its place in historical past with its uncommon trajectory and devastating impression on Tamil Nadu’s shoreline. Rising as a low-pressure space over the southeast Bay of Bengal on November 23, it made landfall close to Puducherry on the night time of November 30. Uniquely, the system stalled upon reaching the coast as a result of a uncommon balanced steering stream, permitting it to take care of its depth even after landfall till the night of December 1. This persistence was fuelled by plentiful moisture from saturated coastal soils, already soaked by previous rains. The stalling cyclone unleashed unprecedented rainfall, with a number of areas throughout Puducherry and Villupuram districts recording 40-50 cm in a single day. Neighbouring districts, together with Cuddalore and Tiruvannamalai, additionally skilled torrential downpours exceeding 20 cm inside 24 hours. The deluge submerged huge stretches of farmland, leading to catastrophic losses for farmers and severely impacting native livelihoods.

The India Meteorological Division (IMD) has established a powerful monitor file for precisely predicting the monitor and landfall of tropical cyclones during the last decade. Regardless of this, Fengal introduced important forecasting challenges as a result of its unconventional monitor, variable pace, and intense rainfall throughout landfall. Whereas IMD efficiently predicted the landfall close to Puducherry almost three days upfront, sure features of the cyclone’s behaviour have been troublesome to forecast. As an example, its north-eastward motion on November 27 was not precisely predicted, and the sluggish development or stalling close to the coast additionally posed challenges.

Extra broadly, climate prediction fashions typically wrestle with forecasting the heavy rainfall related to tropical cyclone landfalls, a limitation that was notably evident in Fengal’s case. Not one of the prediction fashions precisely predicted the distinctive 24-hour rainfall totals exceeding 40 cm recorded in some areas. Limitations in observational knowledge over oceans, and the advanced cloud dynamics inside the cyclone contribute to forecasting difficulties, necessitating steady developments in modeling methods and real-time knowledge assimilation. Two vital areas requiring additional analysis are the prediction of tropical cyclone depth, particularly speedy intensification and forecasting of heavy rainfall related to landfall. These challenges have gotten more and more pressing as IPCC local weather fashions challenge extra intense cyclones, accompanied by heavier precipitation and slower translation speeds.

The post-monsoon cyclone exercise of 2024 highlights the vital want for sustained investments in superior forecasting applied sciences and analysis to handle current data gaps. Regardless of important progress, attaining exact tropical cyclone predictions stays a fantastic problem. It’s crucial to prioritise measures that safeguard lives, livelihoods, and ecosystems from the devastating impacts of tropical cyclones.

(Madhavan Nair Rajeevan was former Secretary to the Authorities of India and presently the Vice Chancellor, Atria College, Bengaluru. E mail: vc@atriauniveristy.edu.in)