Cities make their own weather
Courtesy of NOAA.
JB: This is Earth and Sky. Most experts agree that the burning of fossil fuels is contributing to global climate change.
DB: But we humans affect climate locally, too – for example, with our cities. During the summer, some large cities – such as Tokyo, Mexico City, Phoenix and Atlanta – create rain and storms downwind.
JB: One reason is the well-known “urban heat island” effect, caused by replacing soil, plants and trees with roads, buildings and parking lots. Cities absorb more heat during the day and release it at night. And rising warm air can produce rain. But storms might also result from the vertical structure or so-called “roughness” of cities. Tall buildings force wind upward where it can help form clouds. And a third factor might be fine particles of pollution in cities – they provide seeds for water droplets to form in clouds.
DB: Marshall Shepherd is a NASA research meteorologist. He says even if we don’t know the exact reason for these rainfall anomalies, we can benefit from knowing that they happen.
Marshall Shepherd: Sixty percent of the world’s population will live in cities by 2025. So that means we’re going to have a lot more growth of cities around the world. And if it turns out that cities are affecting rainfall, which is part of the earth’s water cycle, we need to better represent cities and their environments in our weather forecast models and even in our climate models that are trying to project future changes in climate, including rainfall.
JB: That’s our show. We’re Block and Byrd for Earth and Sky.
Our thanks to:
Marshall Shepherd
Research Meteorologist
Deputy Project Scientist for Global Precipitation Measurement
NASA Goddard Space Flight Center
Greenbelt, MD
Additional Teacher Resources
NASA: NASA Satellite Confirms Urban Heat Islands Increase Rainfall Around Cities
NASA researchers have for the first time used a rainfall-measuring satellite to confirm that “urban heat-islands” create more summer rain over and downwind of major cities, including Atlanta, Dallas, San Antonio and Nashville.
Environmental Protection Agency: Climate Change
The EPA Climate Change Site offers comprehensive information on the issue of climate change in a way that is accessible and meaningful to all parts of society – communities, individuals, business, states and localities, and governments.
