School college students wade via stagnated rain water at tsunami rehabilitation colony at Velankanni in Nagapattinam district.
| Photo Credit: M Moorthy
While Tamil Nadu was recovering from the devastation attributable to the tropical cyclone Michaung, one other catastrophic occasion occurred on December 18, this time over the southernmost components of the State. The southern districts of Tamil Nadu — Thoothukudi, Tirunelveli, Tenkasi and Kanyakumari — skilled unprecedented and intensely heavy rainfall on December 17 and December 18. At least 9 rain gauge stations in these districts reported heavy rainfall of greater than 50 cm. The Kayalpattinam station in Thoothukudi recorded 95 cm of rainfall in simply 24 hours. In phrases of chance, this occasion could possibly be termed as a as soon as in a hundred-year occasion. These heavy rains led to large and widespread flooding, precipitated in depth injury, and claimed a number of lives. Due to the heavy rainfall, many villages have been below water and 1000’s of villagers have been with out meals, ingesting water and electrical energy for a few days. The heavy downpour was paying homage to the heavy rains (94.4 cm) in Mumbai on July 26, 2005 by way of the quantum of rainfall.
The trigger
The 2023 northeast monsoon was in an energetic part throughout this episode, characterised by the presence of an east-west trough (or ITCZ). The unprecedented heavy rainfall on December 18 was related to an easterly wave with an embedded cyclonic circulation that moved from the southwestern Bay of Bengal throughout southern Tamil Nadu and Kerala into the southeastern Arabian Sea between December 16 and December 19. There was a large-scale, intense convergence of winds with the inflow of considerable moisture into the area. Most of the latest rains fell within the early morning hours of December 18, supported by the climatological diurnal sample over the area. The north-south operating hills alongside the Tamil Nadu-Kerala border are additionally more likely to have contributed to the dynamics of the heavy rains.
Was this rain occasion precisely predicted? The India Meteorological Department (IMD) had predicted extreme rainfall (greater than 20 cm of rainfall in 24 hours) for December 18 about 48 hours upfront and issued a purple degree warning. But rainfall of greater than 50 cm was not anticipated in any respect. Compared to a tropical cyclone, this climate system was a weaker system. A assessment of the out there numerical climate prediction (NWP) mannequin forecasts confirmed that no mannequin might predict the depth of this heavy rainfall occasion. The fashions solely predicted heavy rainfall within the order of 20-25 cm in 24 hours. However, the numerical climate prediction fashions can not make a quantitative prediction for this type of outlier — 95 cm of rainfall.
Editorial | Turbulence in south: On the heavy rain in southern Tamil Nadu, climate forecasting and preparedness
Probabilistic forecast
For prediction of extremes, a probabilistic strategy is mostly used extensively to calculate the chance of such extreme events occurring in every area. These probabilistic forecasts could be generated using an ensemble strategy, the place we generate a bigger variety of forecasts (30-40 forecasts) with perturbed preliminary situations. The Indian Institute of Tropical Meteorology (IITM) in Pune has developed such a prediction system for making probabilistic forecasts. This ensemble forecasting system was in a position to recommend the excessive chance of incidence of extreme rainfall occasion in southern Tamil Nadu nearly three days upfront. But the prediction didn’t point out 95 cm rainfall in Thoothukudi. We ought to make extra use of those probabilistic forecasts for extreme events as an alternative of counting on quantitative predictions. Probabilistic forecasts present extra lead time, which can be utilized for higher preparation. End customers must be educated to make use of probabilistic strategies for correct mitigation of such extreme events.
The indisputable fact that this occasion is as soon as in a hundred-year occasion doesn’t imply that it may occur solely after 100 years. It might occur subsequent yr too. The IPCC fashions clearly point out that extreme precipitation events might happen extra incessantly as world warming progresses. Heavy rainfall of this magnitude on account of a comparatively weak climate system ought to actually fear us.
Multifaceted strategy
In the face of accelerating extreme rainfall events, it’s crucial that we take a multifaceted and proactive strategy to mitigate the affect and strengthen the resilience of our communities. To meet the problem of local weather change, a complete technique that features strong early warning programs, sustainable city planning, ecosystem conservation, world local weather motion and neighborhood engagement is important to successfully mitigate the impacts of accelerating extreme precipitation events. Robust early warning system may be very very important, however it’s only one part of this complete technique. More analysis is required for higher understanding of the bodily processes of those extreme events. Public consciousness and schooling additionally play an important position in constructing resilience. Communities must be educated in regards to the dangers related to extreme precipitation events and obtain data on the way to put together and reply successfully. Taking proactive measures in the present day will contribute to a extra resilient and sustainable future for generations to return.
(Madhavan Nair Rajeevan was a former Secretary to the Government of India and presently the Vice Chancellor, Atria University, Bengaluru. Views expressed are private)Â
