Singapore:

Climate change is driving changes in rainfall patterns across the world, scientists said in a paper published on Friday, which could also be intensifying typhoons and other tropical storms.

Taiwan, the Philippines and then China were lashed by the year’s most powerful typhoon this week, with schools, businesses and financial markets shut as wind speeds surged up to 227 kph (141 mph). On China’s eastern coast, hundreds of thousands of people were evacuated ahead of landfall on Thursday.

Stronger tropical storms are part of a wider phenomenon of weather extremes driven by higher temperatures, scientists say.

Researchers led by Zhang Wenxia at the China Academy of Sciences studied historical meteorological data and found about 75% of the world’s land area had seen a rise in “precipitation variability” or wider swings between wet and dry weather.

Warming temperatures have enhanced the ability of the atmosphere to hold moisture, which is causing wider fluctuations in rainfall, the researchers said in a paper published by the Science journal.

“(Variability) has increased in most places, including Australia, which means rainier rain periods and drier dry periods,” said Steven Sherwood, a scientist at the Climate Change Research Centre at the University of New South Wales, who was not involved in the study.

“This is going to increase as global warming continues, enhancing the chances of droughts and/or floods.”

FEWER, BUT MORE INTENSE, STORMS

Scientists believe that climate change is also reshaping the behaviour of tropical storms, including typhoons, making them less frequent but more powerful.

“I believe higher water vapour in the atmosphere is the ultimate cause of all of these tendencies toward more extreme hydrologic phenomena,” Sherwood told Reuters.

Typhoon Gaemi, which first made landfall in Taiwan on Wednesday, was the strongest to hit the island in eight years.

While it is difficult to attribute individual weather events to climate change, models predict that global warming makes typhoons stronger, said Sachie Kanada, a researcher at Japan’s Nagoya University.

“In general, warmer sea surface temperature is a favourable condition for tropical cyclone development,” she said.

In its “blue paper” on climate change published this month, China said the number of typhoons in the Northwest Pacific and South China Sea had declined significantly since the 1990s, but they were getting stronger.

Taiwan also said in its climate change report published in May that climate change was likely to reduce the overall number of typhoons in the region while making each one more intense.

The decrease in the number of typhoons is due to the uneven pattern of ocean warming, with temperatures rising faster in the western Pacific than the east, said Feng Xiangbo, a tropical cyclone research scientist at the University of Reading.

Water vapour capacity in the lower atmosphere is expected to rise by 7% for each 1 degree Celsius increase in temperatures, with tropical cyclone rainfall in the United States surging by as much as 40% for each single degree rise, he said.

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)

An aerial view shows the destruction, in the aftermath of the floods in Derna, Libya September 16, 2023. REUTERS/Ayman Al-sahili TPX IMAGES OF THE DAY
| Photo Credit: AYMAN AL-SAHILI

Storm Daniel makes landfall

On September 10, a Mediterranean storm made landfall near the Benghazi city in northeast Libya. It brought record-breaking rainfall to the country. Between September 9 and 11, more than 100 mm rainfall was recorded. The Al Bayda station near the coast saw 414 mm of rainfall, the highest ever recorded in 24 hours. Usually, the region receives just around 1.5 mm of rain for the whole of September.

Nine areas were affected by the storm, and seven were severely affected. Derna city was among the areas severely affected. However, rainfall alone did not cause the destruction in the city.

Dams near Derna collapse

As the storm brought record-breaking rainfall, Al-Wadia dam to the south of the city collapsed. Following this, water rushed down the Wadia valley for around 12 kilometres before reaching the second dam closer to Derna city.

The second dam, too, collapsed under the force of the fast-moving water. With this, the water surged into Derna. The floodwaters destroyed entire blocks. and five bridges along its path.

Estimated deaths have crossed 11,000. More than 38,000 people have been displaced. Around 2,176 structures have been damaged in Derna alone.

Also read |Libya’s deadly floods: what we know

The problem of altitude

Derna’s low-lying terrain made it more vulnerable to flooding. The elevation near the first dam is around 200 m, gradually dropping to around 45 m near the second dam. At Derna’s coastline, elevation is around just 10 m. Combined with this, the Wadi valley acted as an effective conduit in channelling the floodwaters straight into the city.