Chinese air pollution may have exacerbated flooding

Science : In July 2013 Sichuan Province in China experienced the worst flooding in 50 years. Some 200 people were killed; another 300 000 were displaced; and many homes, factories, and bridges were destroyed. Because the Sichuan basin is known for its high level of air pollution, researchers decided to investigate what effect, if any, that may have had on the severity of the event. Jiwen Fan of Pacific Northwest National Laboratory in Richland, Washington, and her colleagues developed two weather system models: one that included the heavy pollution of the present day and one with no pollution. They found that in the dirty-air model, the thick blanket of smoke absorbed much of the sunlight, which kept the ground cooler and suppressed rainfall. As night approached, the moist air mass shifted toward the mountains lining the basin, which triggered the rain to fall—much more heavily and over a shorter period of time than it would have done over the basin. It was the combination of geography and pollution that made the floods so much more severe, Fan says, and those effects need to be taken into account in weather forecasting. The researchers’ findings have been published in Geophysical Research Letters.