By: Juan Declet-Barreto, Anthony J. Brazel, Chris A. Martin, Winston T. L. Chow, Sharon L. Harlan
Phoenix, AZ (June 21, 2013) – Temperatures are heating up in cities across the U.S. as we move into July. Through the support of the National Science Foundation, natural and health scientists in Phoenix, AZ, where temperatures have skyrocketed over the past decade, are studying urban heat islands–and their opposites, park cool islands, where plant growth throws cold water on burning temperatures.
At Arizona State University, researchers conducted microclimate simulations to evaluate the impact of vegetation on lowering temperatures during an extreme heat event in an urban core neighborhood park in Phoenix, Arizona. The research “Creating the park cool island in an inner-city neighborhood: heat mitigation strategy for Phoenix, AZ,” was published in Urban Ecosystems (December 2012).
Metropolitan Phoenix proved an ideal laboratory for investigation, as rapid urbanization has replaced natural vegetation and agricultural fields, increasing summer temperatures during the past 50 years.
They predicted air and surface temperatures under two different vegetation regimes: existing conditions representative of Phoenix urban core neighborhoods, and a proposed scenario informed by principles of landscape design and architecture and Urban Heat Island mitigation strategies.
Researchers found significant potential air and surface temperature reductions between representative and proposed vegetation scenarios: 1) a Park Cool Island effect that extended to non-vegetated surfaces; 2) a net cooling of air underneath or around canopied vegetation ranging from 0.9 °C to 1.9 °C during the warmest time of the day; and 3) potential reductions in surface temperatures from 0.8 °C to 8.4 °C in areas underneath or around vegetation.
Larger plants such as trees absorb and reflect the sun’s rays, buffering the heat index. Scientists call it a “microclimate ecosystem service,” or shade. Trees also reduce hot air by turning water from liquid to gas inside their leaves, causing temperatures to fall in the immediate environment.
Extreme heat, scientists have found, is a threat to human health, increases atmospheric pollutants and energy and water use, alters regional hydrology and affects interactions between humans and ecological processes.
The research suggests that climate intervention strategies should be targeted at low-income neighborhoods where vulnerability to heat is greater. The researchers recommend creating park cool islands filled with shade trees and vegetation as an intervention strategy for urban heat island mitigation that could be supported with public resources.
Sources and Related Resources
Creating the park cool island in an inner-city neighborhood: heat mitigation strategy for Phoenix, AZ
Summertime: Hot Time in the City – Parks are islands of coolness in cities’ urban heat