More than 900 people are dead, thousands more missing and millions affected by a band of cyclones and extreme monsoonal weather across southern Asia. Torrential rain has triggered the worst flooding in decades, accompanied by landslides. Indonesia, Sri Lanka, Thailand, Vietnam and Malaysia have been hit hardest. The death toll is likely to rise significantly.
Normally, cyclones don’t form close to the equator. But Cyclone Senyar formed just north of the equator in the Malacca Strait. It triggered lethal flooding in Sumatra and peninsular Malaysia last week.
It wasn’t alone. Other tropical cyclones formed along a zone of converging trade winds north of the equator. Typhoon Koto caused severe flash floods and landslides in the Philippines before weakening as it neared Vietnam. Tropical Cyclone Ditwah devastated Sri Lanka. One reason Sumatra was hit by such severe flooding was due to the unusual interaction between Typhoon Koto and Cyclone Senyar, which has now weakened.
The near-simultaneous emergence of these intense storms isn’t unheard of, and equatorial cyclones are rare but known. But the devastation is extraordinary. Sri Lankan President Anura Kumara Dissanayake described the floods as the “most challenging natural disaster” in the country’s history. Is there a climate link? We don’t know yet, but we do know climate change is projected to trigger fewer cyclones overall, but with higher intensity.
Cyclones, typhoons and hurricanes are different names for the same strong, spinning tropical storms. These storms form over large expanses of warm water – but not usually on the equatorial seas.
This is because there’s not enough Coriolis force from Earth’s rotation at the equator to spin storms into their classic cyclonic structure.
The closest cyclone to the equator was the 2001 Tropical Storm Vamei which formed at just 1.4°N. Cyclone Senyar formed at 3.8°N.
While tropical cyclones can form in any month, they’re more common between July and October in the northwest Pacific and North Indian oceans. Cyclone Senyar and Typhoon Koto formed in the Northwest Pacific Basin, which has the largest, most frequent and most intense tropical cyclones in the world. Several devastating typhoons have hit the Philippines and parts of southern China this year.
One reason these cyclones have caused widespread damage is because they have hit countries where cyclones are rare, such as Indonesia and Malaysia.
Tropical cyclones are often smaller and much less common in the North Indian Ocean, including the Bay of Bengal and Arabian Sea. But Cyclone Ditwar tracked directly down Sri Lanka’s east coast, magnifying the damage.
As the world’s oceans and atmosphere warm at an accelerating rate due to the rise in greenhouse gases from burning fossil fuels, tropical cyclones are expected to become more intense.
This is because cyclones get their energy from warm oceans. The warmer the ocean, the more fuel for the storm.
The warming atmosphere is supercharging the global water cycle, and peak rainfall rates are increasing. When more rain falls in a short time, flash flooding becomes more likely.
We can’t immediately say climate change made these storms worse, as it takes time to pinpoint any link.
