Here Comes the Urban Rain Again
- By AMS Staff
- Dec 23, 2024
1. Ho Chi Minh City, Vietnam
2. Kuala Lumpur, Malaysia
3. Lagos, Nigeria
4. Guangzhou-Shenzhen, China
5. Sydney, Australia
—Cities (among the 100 largest in the world) with the greatest positive urban annual precipitation anomalies, according to a recent study in the Proceedings of the National Academy of Sciences. Researchers studied satellite rainfall data for 1,056 cities across the globe for the years 2001–20, and found that 63% exhibited an “urban wet island” effect, meaning they received more annual precipitation in and downwind of their urban areas compared to bordering rural areas. Ho Chi Minh City experienced the greatest difference, averaging 274 millimeters (10.8 inches) of extra yearly precipitation compared to its rural surroundings. The highest-ranking U.S. cities were Houston (8th) and Miami-West Palm Beach (10th). “This is everywhere,” notes coauthor Dev Niyogi of the University of Texas at Austin. “The magnitude of the impact will vary. But just the way we treat urban heat island, we should start treating urban rainfall effect as a feature associated with urbanization.” While this urban precipitation effect has been studied at small scales, this is the first research to examine the phenomenon globally. The researchers found that the magnitude of the effect nearly doubled in the studied time period, which they attribute to both increased urbanization and warmer temperatures. The study also showed a drying effect in some cities, with Seattle showing the greatest deficit, although the effect was most often in valley and lowland cities where nearby mountains impact precipitation more than the urban footprint itself. The increase in precipitation is caused by a number of factors, including heat radiating from city infrastructure causing increased convection, pollution seeding clouds, and large buildings and uneven landscape that cause storms to stall. “Cities can make a storm on steroids,” Niyogi says. [Sources: The Washington Post, Bloomberg]
PHOTO CREDIT: Photo Credit: iStock.com/1001slide