White Roofs in Cities Could Reduce Rainfall

Sunset over Phoenix, Arizona.<a href="http://www.shutterstock.com/pic-72235192/stock-photo-the-city-of-phoenix-az-at-sunset.html?src=385a5f28a336f38517f051df5db65582-1-59">Action Sports Photography</a>/Shutterstock


This story first appeared on the Atlantic Cities website and is reproduced here as part of the Climate Desk collaboration.

You don’t really need to know much about the urban heat island effect to understand that Arizona is feeling it.

With both a rapidly expanding urban footprint and some of the highest temperatures in the country, the increasingly studied feedback loop of city surfaces absorbing heat and raising temperatures is in hyperdrive in Arizona. Mitigating the heat-holding effects of urban growth has become a high priority in the state’s metropolitan areas, and various efforts are underway to prevent some of that heat from soaking into the sponge that is the paved and built urban environment. But these efforts could also be making the region’s overall environmental future worse.

According to new research out of Arizona State University, efforts to improve the reflectance of Arizona’s cities by painting roofs white may be reducing rainfall across the state.

Published recently in the journal Environmental Review Letters, the study finds that average rainfall statewide could drop by as much as 4 percent if roof painting efforts continue. The increased reflectivity of these roofs has been found to modify hydroclimatic processes in the region by reducing what’s called evapotranspiration, or how much water evaporates back into the air from the land and its plants.

The researchers looked specifically at the “Sun Corridor”—the metropolitan areas of Phoenix, Tucson, Prescott and Nogales. By projecting growth and urban expansion models out to 2050, the researchers warn that overall precipitation could go down as the use of this white roof mitigation measure spreads across the growing urban footprint.

The researchers also note that the urban heat island itself is a major cause of reduced rainfall in the region. If urban expansion reaches the projected growth the region’s association of governments is expecting, the researchers say that urban heat island effects could result in a 12 percent reduction in rainfall averaged across the state.

Combating the urban heat island effect will be incredibly important for growing places like Arizona. Though this research shows that white roofs are effective at reducing urban heat island effects, there may also be side effects of this mitigation approach that shouldn’t be ignored.

More Mother Jones reporting on Climate Desk

ONE MORE QUICK THING:

Or at least we hope. It’s fall fundraising time, and we’re trying to raise $250,000 to help fund Mother Jones’ journalism during a shorter than normal three-week push.

If you’re reading this, a fundraising pitch at the bottom of an article, you must find our team’s reporting valuable and we hope you’ll consider supporting it with a donation of any amount right now if you can.

It’s really that simple. But if you’d like to read a bit more, our membership lead, Brian Hiatt, has a post for you highlighting some of our newsroom's impressive, impactful work of late—including two big investigations in just one day and covering voting rights the way it needs to be done—that we hope you'll agree is worth supporting.

payment methods

ONE MORE QUICK THING:

Or at least we hope. It’s fall fundraising time, and we’re trying to raise $250,000 to help fund Mother Jones’ journalism during a shorter than normal three-week push.

If you’re reading this, a fundraising pitch at the bottom of an article, you must find our team’s reporting valuable and we hope you’ll consider supporting it with a donation of any amount right now if you can.

It’s really that simple. But if you’d like to read a bit more, our membership lead, Brian Hiatt, has a post for you highlighting some of our newsroom's impressive, impactful work of late—including two big investigations in just one day and covering voting rights the way it needs to be done—that we hope you’ll agree is worth supporting.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate