Research Finds that Rain is Drawn to Many Big Cities

It’s well-known that urban areas are often hotter than the surrounding countryside, but new research by the Jackson School of Geosciences has shown that they can be wetter too, sometimes markedly so.

The study published in Proceedings of the National Academy of Sciences looked for evidence of precipitation anomalies in 1,056 cities across the globe and found that more than 60% received more rain than their surrounding rural areas.

The difference in rainfall is generally more pronounced in hotter, wetter areas. For instance, researchers found that Houston, on average, receives almost 5 inches more rain per year than its surrounding rural areas. Other large cities in that list include: Ho Chi Minh City, Vietnam; Kuala Lumpur, Malaysia; Lagos, Nigeria; and the Miami-Fort Lauderdale-West Palm Beach metropolitan area.

The rain-drawing effect could have wide-ranging implications, including worsened flash flooding in densely built urban areas.

There are several reasons why most cities receive more rainfall than their rural neighbors, said co-author Zong-Liang Yang, a professor in the Department of Earth and Planetary Sciences, including the presence of tall buildings, which block or slow wind speeds and lead to a convergence of air toward the city center, which promotes cloud formation.