‘Not normal’: Climate crisis supercharged deadly monsoon floods in Asia | Climate crisis

The climate crisis has amplified deadly storms that have killed more than 1,750 people in Asia by making downpours more intense and flooding even more severe, scientists have reported. Monsoon rains often lead to flooding, but scientists were clear this was “not normal”.

In Sri Lanka, some flooding reached the second floors of buildings, while in Sumatra, Indonesia, flooding was made worse by the destruction of forests, which in the past slowed the flow of rainwater over the hills.

Millions of people were affected when Cyclone Ditwah hit Sri Lanka and Cyclone Senyar hit Sumatra and Peninsular Malaysia in late November, and these events became one of the deadliest weather disasters in recent history.

The analysis by World Weather Attribution, a consortium of climate scientists, found that the intensity of five-day heavy rain events increased by 28 to 160 percent in the region hit by Cyclone Senyar due to human-caused global warming. In Sri Lanka, periods of heavy rain are now between 9 and 50% more intense.

Although at least 1,750 people have died in the floods and hundreds more remain missing, cyclones also have a significant and lasting impact on health. Recent studies have shown that deaths from, for example, diabetes and kidney disease increase after such storms. Many people have also lost their homes and livelihoods, with the poorest worst affected.

“The combination of heavy monsoon rains and climate change makes for a deadly mix,” said Dr Sarah Kew, an academic at the Royal Netherlands Meteorological Institute and lead author of the study. “Monsoon rains are normal in this part of the world. What is not normal is the increasing intensity of these storms.”

Professor Lalith Rajapakse, from the University of Moratuwa in Sri Lanka, who participated in the study, said: “Cyclones like Ditwah have become an alarming new reality for Sri Lanka and the entire South and Southeast Asian region, leading to unprecedented rainfall, widespread loss of life and massive disruption to economic activities. »

“Flooding is quite common with us every year during the monsoon season: we expect some flooding, but up to about 1 foot to 2 feet maximum,” he said. “But this time what happened was that in some areas the height exceeded 14 to 15 feet. So even not reaching the second floor could sometimes save those affected.”

Scientists agree that the climate crisis, caused by the burning of fossil fuels, is making precipitation heavier and more intense in many parts of the world. Warmer air can hold more moisture, making the rain heavier.

For the study, researchers examined weather records to assess how periods of heavy rain have changed as the planet has warmed to the 1.3°C observed today, and found a significant increase in intensity. The range of estimates, from 28 to 160% in the region affected by Cyclone Senyar, for example, is due to the use of a range of meteorological data series.

Climate models are used in these studies to estimate the likelihood of extreme weather events being caused by global warming. In this case, the models did not reproduce the events well, with natural fluctuations in ocean temperatures – La Niña and the Indian Ocean Dipole – being complicating factors.

However, analysis of weather data and measurements of rising ocean temperatures allowed scientists to conclude that global warming had increased the downpours caused by cyclones.

Dr Mariam Zachariah, from Imperial College London, said: “These events illustrate how climate change and natural variability can align to produce exceptional rainfall. Although natural variability is inherent to the climate system, reducing reliance on fossil fuels is within our power and necessary to reduce the intensity of future extreme events.”

Maja Vahlberg, of the Red Cross Climate Centre, said: “Large parts of Sri Lanka and Indonesia have experienced devastation on a scale that very few people living there have seen in their lifetime. Unfortunately, it is the most vulnerable people who are experiencing the worst impacts and have the longest road to recovery.”

She highlighted two factors that have worsened the impacts: the migration of people to cities and the destruction of forests: “Over the decades, growth has increasingly occurred in low-lying floodplains, deltas and river corridors. These areas are economic hubs, with roads, power lines, hospitals, markets. But they are also natural pathways for floodwaters.”

“Deforestation and wetland loss also reduce the ability of land to absorb water on hillsides,” Vahlberg said. “This increases the risk of landslides, and downstream it raises flood peaks and carries debris into populated areas of Sumatra.”

Initial estimates of damage in Sri Lanka were $6-7 billion, or 3-5% of national GDP, Rajapakse said: “This should be an unequivocal revelation on the scale of future climate extremes for which the country and the region must prepare. »