Rooftop considerations amidst climate change
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.
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.