Too much pollution makes us cough and wheeze, but did you know that it can also change our weather? In July 2013 Beichuan County, a mountainous region in southwest China, was devastated by a catastrophic flood, with 94cm of rain falling in just two days. It was the worst flood the region has seen in over five decades. Nineteen people lost their lives and the city of Qushan was submerged under 7m of water.
A model of this extreme weather event shows that it was driven by excessive pollution in the neighbouring Sichuan basin. Running the model first with clean air and then with the choking Sichuan haze, scientists found that the heavy air pollution increased rainfall over the mountainous region by as much as 60% in July 2013.
In this case the pollution was absorbing solar radiation and making the atmosphere above the Sichuan basin more stable, preventing moist air from falling as rain. “The pollution is redistributing the precipitation from large areas of the plains to a narrow area at the foothills, which results in the heavy flooding,” says Daniel Rosenfeld from the Hebrew University of Jerusalem in Israel, whose findings were published in Geophysical Research Letters.
Meanwhile, another study in the same journal has shown that the swarm of 120 tornadoes that swept the southeastern US in April 2011, killing 313 people, was prompted by extensive biomass burning in central America, which changed cloud structure and increased the chances of tornado formation.
Pollution modified weather is becoming more common everywhere, but the trend could be quickly reversed if we cleaned up our skies.
