How a cocktail of rogue storms and climate chaos unleashed deadly flooding across Asia

Hundreds of people remain missing – likely washed away in rapid torrents of floodwater or buried beneath thick mud and debris.

CNN) — Looking at the weather map on his computer and seeing three tropical storms forming simultaneously across Asia in late November, climatologist Fredolin Tangang’s first thoughts drifted to the 2004 disaster movie “The Day After Tomorrow.”

The film, in which three massive storms plunge the earth into a new ice age, goes beyond the realms of reality. But there was something about the formation of these weather systems swirling across his screen that made Tangang sit up.

They were not the strongest storms this year. But they were “unusual,” said Tangang, emeritus professor at the National University of Malaysia.

One was churning near the equator off the coast Indonesia – an area where storms rarely take shape because the planet’s spin is too weak there to whip them into existence. Another was tracking for parts of Sri Lanka that are rarely hit by tropical storms. The third was late in the season, and on course to dump yet more rain on already soaked terrain in Vietnam and the Philippines.

“You realize this is like a monster,” Tangang said.

The cyclonic storms went on to unleash torrential rains and catastrophic flooding – including, in one area, the second-wettest day recorded anywhere in history – across swathes of South and Southeast Asia. They killed more than 1,700 people, according to a CNN tally from disaster agencies’ figures.

Multiple countries are struggling to recover from their worst flooding in decades. Hundreds of people remain missing – likely washed away in rapid torrents of floodwater or buried beneath thick mud and debris.

The region is used to monsoon rains and frequent flooding, but the enormity of the human toll and level of destruction have shocked many, with scientists warning that, as the climate crisis intensifies, more intense extreme weather events will become the new normal.

“This is a human tragedy. It’s multiple conditions happening at the same time, and that makes it rather unprecedented,” Tangang said.

Rare storms in unusual places

“Relentless,” “rare” and “record-breaking” are the words that scientists have used to describe the biblical deluges across thousands of miles from Sri Lanka to Indonesia, Malaysia, Thailand, Vietnam, and the Philippines.

Driving the disaster, experts say, was an extraordinary mix of overlapping powerful weather systems, amplified by the man-made climate crisis.

Tropical Storm Senyar formed just north of the equator in the Strait of Malacca, the waterway between Indonesia’s Sumatra and the Malaysian peninsula – a rare occurrence that may have helped magnify the disaster as communities there weren’t used to experiencing cyclones, Tangang said.

Storms rarely take shape near the equator, because the planet’s spin is too weak there to provide the Coriolis force that gets a cyclone rotating.

In another unusual twist, the storm made a U-turn and moved south and eastwards – highly uncommon in this part of the world, where the earth’s rotation means storms tend to track west and move northwards, he added.

Meanwhile, Cyclone Ditwah was creeping along Sri Lanka’s east and north coasts, dumping massive bands of rain onto low-lying, beachy coastline and central hill country – an area that was similarly not experienced in dealing with tropical storms.

Typhoon Koto’s rains triggered flooding and landslides in the Philippines, which had suffered back-to-back deadly typhoons and extensive flooding, before it moved toward an already saturated Vietnam.

A cold surge in the weeks before had blown strong winds from the north across the South China Sea, where they collected moisture and dumped it in the form of rain over Thailand and Malaysia.

An already soaked region

In early November, two major typhoons in less than a week carved a path of destruction through the Philippines. Fung-wong’s footprint spanned nearly the entirety of the archipelago, and Kalmaegi killed at least 200 people before hitting Vietnam as one of the strongest typhoons on record there.

Communities in central Vietnam had barely recovered from widespread flooding and landslides that killed at least 90 people, submerged historic neighborhoods and devastated farmland.

One meteorological station in central Vietnam recorded a national 24-hour rainfall record of 1,739 millimetres, according to Clare Nullis, World Meteorological Organization spokesperson.

“That’s really, really enormous. It’s the second-highest known total anywhere in the world for 24-hour rainfall,” she said at a briefing in Geneva.

Like a sponge full of water, the land could not take any more moisture. People had lost their homes and livelihoods and were facing yet more loss.

Then came Koto, Senyar, and Ditwah, which “created back-to-back pulses of rainfall that hit already saturated river basins,” said Joseph Basconcillo, a senior weather specialist at the Philippine Atmospheric, Geophysical and Astronomical Services Administration.

“Once the surface was soaked, additional rain quickly turned into severe flooding.”

Surging flash floods and landslides quickly overwhelmed entire communities, catching many people off guard.

“The combination of unusual storm tracks and vulnerable landscapes made the impacts far more extreme,” said Basconcillo.

Adding to the chaotic cocktail, two natural climate phenomena that usually bring above-average rainfall to the region were occurring simultaneously: La Niña and a negative Indian Ocean Dipole.

La Niña and the negative Indian Ocean Dipole cannot explain the disaster alone, but they “created a background environment that made intense rainfall more likely,” said Basconcillo. “The worst impacts occurred when this moisture aligned with strong storms and vulnerable terrain.”

In Hat Yai, in Thailand’s southern Songkhla province, floodwaters as high as eight feet surged through the streets, which resident Wassana Suthi described as “like a tsunami.”

In Sumatra, Indonesia – the worst-hit country, where at least 883 people were killed – rescue teams are still trying to reach villages cut off by washed-out roads and collapsed bridges. Abdul Ghani, a resident of Palembayan town in West Sumatra, spent days looking for his missing wife, showing a photo of her to everyone he met. “I hope they find her body, even if it’s just a piece of her hand,” he told the news agency Reuters.

A thousand miles away on the other side of the Indian Ocean in Sri Lanka, neighborhoods were swept away and residents continue the search for bodies in the thick mud and debris.

“We could only hear a sound like thunder,” Nawaz Nashra, from Alawathugoda village in Kandy, told Reuters. “The house next to ours collapsed as we watched. There was no time to warn anyone.”

‘Accumulation of catastrophic events’

Southeast and South Asia are among the most vulnerable places on earth to the impacts of the human-caused climate crisis, for which rich, industrialized nations bear greater historical responsibility.

Asia is warming almost twice as fast as the global average. Hotter ocean temperatures provide greater energy for storms to strengthen, and climate change is supercharging rainfall events as the warmer air can hold more moisture, which it then wrings out over towns, cities and communities.

Researchers say they are now seeing a pattern unfolding: an “accumulation of catastrophic events.”

“What we’re witnessing in Southeast Asia is a relentless cycle of storms: weeks of heavy rainfall during an extreme monsoon season, with record-breaking events happening time and time again,” Davide Faranda, research director at the French National Center for Scientific Research said in a statement. “This cannot be accepted as the norm.”

An urgent phase-out of fossil fuels, which release planet-heating pollution, is vital to stave off the worst of the climate crisis. But greater investment is also needed to help vulnerable countries adapt to the impacts already happening year after year.

“As climate change increases the intensity of heavy rainfall events, investments in stronger warnings, better land-use planning, upgraded infrastructure, and nature-based solutions become essential,” said Basconcillo.

Other man-made factors likely exacerbated the disaster, including environmental degradation and rampant deforestation – often worsened or abetted by official corruption.

In Indonesia, residents and government officials have pointed to the decades of deforestation from illegal logging, mining and palm oil plantations on Sumatra that has degraded the landscape, leaving hillsides more prone to flooding and landslides. Similarly in the Philippines, hundreds of thousands of people have taken to the streets protesting corruption over flood control projects. Meanwhile, Sri Lanka is only starting to rebound from its worst financial crisis in seven decades, that has left little for funding infrastructure or public health, according to the World Bank.

At the COP30 summit in Brazil last month, the world struck a new deal that called for a tripling of funds to help countries adapt to increasingly severe climate impacts. But countries failed to agree to a roadmap away from fossil fuels, and there were no explicit commitments on deforestation or funding pledges.

“The science is really clear, things are getting worse,” said climatologist Tangang. “It’s time for the world, for governments to be serious in not only in fixing the climate but to ensure that their own backyard is ready to face the impacts of climate change,” he added.

“We don’t want countries getting poorer, people getting poorer, and more families losing their lives because of this.”

This week, more rains are forecast for Sumatra and Sri Lanka. A fresh storm is brewing to the east of the Philippines.

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