Soot and air pollution may have caused China’s worst flood in 50 years, according to a recent study. In July 2013, a mountainous region in the Sichuan province was pounded by 94 cm of rain over the course of five days, floods that left 200 dead and 300,000 others displaced.
Researchers led by Jiwen Fan from Pacific Northwest National Laboratory in Richland, Washington simulated the atmosphere over the heavily industrialized Sichuan basin with varying levels of emissions and found that had it not been for the amount of smoke, greenhouse gases, and aerosols spewed from factories in the area, rainfall of the storm would have been 60% less.
“We were amazed at the scale of the effect the pollution had,” Fan told Science. “Effectively it redistributed the precipitation from the wide area of the basin into the mountains.”
The Sichuan basin—home to over 100 million people and heavy industries like iron, steel, and energy production—is surrounded by mountains that trap aerosols in the air above it and allow moisture to build up. According to Fan’s simulation, as the weather system reached the mountains, it unleashed all that pent-up precipitation, resulting in a day’s worth of rain falling in a few hours on one area.
Other researchers have also pointed to potential connections between air pollution and weather. Air pollution may be causing monsoons to hit South and East Asia earlier and harder. Others have linked aerosols in the atmosphere to the intensity of tornadoes and tropical cyclones. (Some studies, though, have found that air pollution may have suppressed hurricanes from forming over the Atlantic Ocean.)
Fan believes that the deadly floods that hit Pakistan two months after the Sichuan flood may have also been caused by air pollution and unlucky geography.
For China, it’s another reason to reduce air pollution, which is already blamed for over 400,000 premature deaths a year. Fan and her research team advise officials to ratchet up their war on pollution as a way to mitigate the impact of these disasters in the future.