Music of monsoon gives way to lurking fear

Changing climate appears to be moving the State towards excessive rain and droughts

Updated - September 16, 2022 09:13 am IST

Published - September 15, 2022 09:04 pm IST

Extreme weather events are on the rise with the warming climate. A motorist negotiating heavy rain in Kottayam. File photo

Extreme weather events are on the rise with the warming climate. A motorist negotiating heavy rain in Kottayam. File photo | Photo Credit: Vishnu Prathap

Sometimes, it blows as an inescapable drizzle, whipping in sideways streaks across the window. At other times, it just darts down the sky, stirring to life the strikingly green landscape underneath. 

Gone are the days when the drizzling music of the rain evoked a sense of nostalgia. The monsoons, which have drenched Kerala in a rare natural bounty every year, are no more the recurring motif of this tropical State.

According to experts, the changing climate appears to be moving the State towards the worst of both worlds — excessive rain and droughts. And the story of how the recurring floods since 2018 have brought the State to its knees is about to get a lot more familiar.

Scientists are pointing to a basic meteorological principle: as temperature rises, more water evaporates from the sea and, hence, more water is available for heavier rain. The precipitation story, however, is turning out to be even more complex with the forecasting of these punishing spells becoming notoriously difficult.

“The decades ahead are going to witness more extreme rainfall, more higher temperatures, increased warming over the Indian Ocean, rising sea levels, and greater frequency and intensity of cyclones in the Arabian Sea,” says Roxy Mathew Koll, a senior scientist at the Centre for Climate Change Research at the Indian Institute of Tropical Meteorology, Pune.

The monsoon, according to him, has just not been able to retain its uniformity as both the ocean and atmosphere continue to warm. The experience of the central Travancore mid-lands in August this year, which witnessed continuous showers for almost a couple of weeks followed by a severe drought spell, was indicative of this pendulous regime.

The drought spell, which lasted another couple of weeks, came to a close with a mini cloud-burst of sorts that dumped over 117 mm of rain in just six hours on August 27 midnight. The phenomenon also triggered flash floods across the region ranging from Pampady in Kottayam to Mallappally in Pathanamthitta, besides the other low-lying parts of the region.

Nearly a week later, a similar event played out along the forest fringes of Pathanamthitta, which received 170 mm of rain in just four hours.

“What we are witnessing now are the local manifestations of a global event and the projections suggest that this is the prologue of a future story. To carry out a robust statistical analysis to get a clear view of the subtle details and trends in the rainfall pattern, we need more data,” adds Mr. Koll, also the lead author of the Intergovernmental Panel on Climate Change special report on the Ocean and Cryosphere in a Changing Climate.

The changing climate properties, according to him, appear to be conspiring to give a new meaning to the age-old expression; when it rains, it pours. And as the drops fall too quickly for soil to absorb, the earth is unable to soak it all up. Instead, the run-off water collects and flows through different routes, increasing the risk of floods and soil erosion.

Most extreme rainfall spells are coming to Kerala with the occurrence of active Madden Julian Oscillation (MJO) phases over the equatorial Indian ocean, as per a study by researchers from the ‘satellite remote sensing and applications group’ of the Advanced Centre for Atmospheric Radar Research, Cochin University of Science and Technology.

MJO is an eastward propagating convective system that passes over the Indian and Pacific Oceans with a periodicity of 30–60 days and influences most of the tropical weather systems.

Unlike the depression that systematically strengthens and decays over the Bay of Bengal, active MJO phases can generate cumulonimbus clouds over Kerala that can result in very heavy rainfall over a short duration. The occurrence of an active MJO phase during September-November, meanwhile, also has the potential of delaying the withdrawal of monsoon.

“The MJO induced extremes are only expected to strengthen in the coming years with the warming ocean and its impact will be most felt across the south and central Kerala region,” says Ajil Kottayil, who led the study.

Gopakumar Cholayil, senior scientific officer with the Academy of Climate Change Education and Research of Kerala Agriculture University, says the future has hit home at least a decade too soon. Incidents of 100 mm rain a day were so rare till the first decade of this century, while it has now come down to a boom-or-bust-type precipitation pattern, he says.

“The Arabian sea now stands a notch above the Bay of Bengal in the table of temperature anomaly and this means there is an abundant supply of moisture to the air from the West. This, combined with the unstable atmosphere is giving rise to more cumulus clouds that are delivering more water eastwards,” he says.

With the warming climate, rainfall also shows a tendency to become less distributed and to be more concentrated on some days. “Kerala thinks it knows the rain. But the fluctuating climate begs to differ. Its impact on the livelihood of people, especially in the primary sector, is going to be catastrophic and steps should be initiated at the grassroots level,” he says.

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