Beijing’s size may have exacerbated recent storm

Nature : Large cities can intensify the severity of rainstorms, as evidenced by the 21 July event that deluged Beijing. Fei Chen, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colorado, and colleagues conducted a study last year of the impacts of urbanization on precipitation. Their study applies equally well to July’s storm, which dumped 215 millimeters of rain on Beijing in 16 hours and killed at least 77 people. According to Chen, large urban areas become heat islands because of the loss of green vegetation to concrete and asphalt and because of increased warming from cars, industry, and air conditioning. High-rise buildings exacerbate the effect. By impeding a storm’s movement, they concentrate rainfall in one place and funnel heat up into the air, which can invigorate atmospheric circulation and force clouds to higher altitudes where they produce more rain. “If Beijing were less developed, the storm would probably be just a passing event, with much less rain falling in the city,” said Chen.