As the realities of climate change set in, so too are
realizations that building technologies impact both internal and external
environments. The percentage increase of asphalt and blacktopped roofs create
urban heat islands. Resultantly cities have become earth’s newest desserts
exhibiting high temperatures and arid conditions with little vegetation. Urban
expansion as a stand-alone factor (omitting greenhouse gas-induced climate
change considerations) is expected to raise temperatures by roughly six degrees.
Because of this, scientists are now exploring new technologies to cope with the
new reality.
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According
to Matei Georgescu, sustainability scientist at Arizona State University, “Life
in a warming world will require human ingenuity to adapt to the new realities.
Greenhouse gas-induced warming and the expansion of the megalopolis are
significant drivers of our warming planet; we need to find adaptation
technologies that will help us acclimate.”
Considering
adaptive technologies like cool roofs, including white roofs, green roofs
(planted with vegetation) or green/white hybrids has brought much thoughtful
discussion. Do they work? If so, how well? Georgescu is collaborating with
colleagues to determine the effectiveness of common adaptation technologies to
reduce warming caused by urban expansion through a National Science Foundation
(NSF) Water Sustainability and Climate (WSC) grant.
Georgescu findings
show performance differences between cities, regions and seasons matters in choosing
the most efficient roof design.
“The
effects of cool roofs extend beyond surface temperatures to rainfall and energy
demand. There are trade-offs that are often unaccounted for,” says Georgescu.
Painting
roofs white is one easy and effective strategy to reflect incoming solar
radiation and decrease energy demand during summer months in the southwestern
United States. But according to
Georgescu, “in more northern locations, this strategy in winter further
cools the environment, leading to a need for additional heat to keep buildings
warm.”
Therefore
in areas where the white roof doesn’t satisfy year round concerns, green roofs might
be a better solution. While green roofs will not cool the environment, as much
during the summer as a white roof, they also won’t leave roofs as cold in the
winter providing a greater year round consistency.
Heating
and cooling isn’t the only consideration though. In Florida where one might put
a white roof to minimize heat, Georgescu found white roofs have “led to a decrease
in rainfall by a considerable amount each day–almost 50 percent. That has
implications for water availability, stream flow and ecosystems.”
Georgescu’s
experience has led him and his team to conclude that there is no
“one-size-fits-all” solution to counteract climate change in the urban
environment. Each region requires consideration of multiple geographic factors.
Read
more at Reseach.gov
NSF.
Urban rooftop garden via Shutterstock.