Researchers from Pacific Northwest National Laboratory and their collaborators in Israel and China have found that heavy human-caused air pollution over the Sichuan Basin just upwind contributed to the catastrophic 2013 Sichuan Flood that killed up to 200 people with hundreds more missing. The flood was a 50-year event with up to 17 inches of rain from 8-13 July, causing mudslides and disrupting the lives of more than 6 million people.
Led by the PNNL team, the researchers carried out model simulations of the catastrophic flood event and associated sensitivity simulations. They conducted ensemble simulations at a convection-permitting scale (3 km) using the improved chemistry version of the Weather Research and Forecasting Model (WRF-Chem), a regional-scale model.
They found that through a series of events they call “aerosol-enhanced conditional instability,” tiny particles from heavy air pollution absorb heat from the sun, stabilize the atmosphere, and suppress local storms during the daytime. However, this allows the heavy moist and now warm air to be transported downwind to mountainous areas where it is lifted causing extreme nighttime precipitation. The research was published in Geophysical Research Letters and highlighted by Nature.
We found a mechanism that could escalate a normal storm event to a severe weather event, particularly in downwind mountainous areas where storms can be triggered by the topography.—Dr. Jiwen Fan, PNNL atmospheric scientist and lead author
The study establishes a clear connection between severe air pollution and extreme weather events. While this finding covers Southeast China, the mechanism that triggers the extreme weather events would apply to other regions in developing countries with similar topography and pollution levels.
Fan J, D Rosenfeld, Y Yang, C Zhao, LR Leung, and Z Li (2015) “Substantial Contribution of Anthropogenic Air Pollution to Catastrophic Floods in Southwest China.” Geophysical Research Letters doi: 10.1002/2015GL064479