Summer in the city: Preparing for extreme heat
Each year in the United States, more people die from heat waves than from any other type of natural disaster, according to the Centers for Disease Control and Prevention. The National Climate Assessment projects an increase in the risk, intensity, and duration of extreme heat events over the next century. Elderly populations are especially at risk for heat-related morbidity and mortality because of changes in how the body regulates temperature as it ages; seniors are also more likely to live alone, have reduced social contacts, and have medical conditions like heart or renal disease.
Both people and buildings need to be resilient to heat storms; this involves improving personal health and reducing thermal exposure. Although preexisting medical conditions are a critical factor in temperature-related morbidity and mortality, this article focuses on how architects can help to reduce exposure to high temperatures through effective design of the built environment.
City and Local Strategies
At the city level, the urban heat island effect increases exposure to temperature. Urban heat islands are broadly defined as the temperature difference between urbanized areas and their rural surroundings. Urban heat islands are a byproduct of all human settlements; they increase temperature exposure during heat waves, spur electrical demand associated with air-conditioning, and generate more smog at the ground level.
Common design strategies such as increasing the tree canopy, reducing the amount of paving, and cool roofing materials can help to lower local temperatures. These measures also provide environmental benefits like reducing air pollution and stormwater runoff.
At the neighborhood level, cooling centers can help to reduce personal exposure to high temperatures and humidity. Cooling centers have been shown to be effective during extreme heat events; in the 1995 heat wave in Chicago they cut the risk of dying in half (Semenza, Rubin et al. 1996).
However, not all residents have access to cooling centers because of limited mobility or a lack of transportation options. Architects can combat these problems by working with local officials to ensure that public buildings are accessible and by advocating for universal design; they can also lobby local officials to improve public transportation options.
Cooling the Home
At the household level, air-conditioning is an effective strategy to reduce heat-related illness. While many homes in the United States have air-conditioning systems, they are less common in low-income populations. A number of cities distribute free window air-conditioners to senior citizens and low-income residents; while this may eliminate first cost as a barrier, energy costs may be a longer-term issue.
Although the Low Income Home Energy Assistance Program provides federal funding to low-income households to pay utility bills, this assistance does not address a broader issue: air-conditioning systems have strained electrical distribution systems in the United States. Therefore, alternatives to residential air-conditioning are critical because these “passive” systems do not require electricity to provide a protective effect and could continue to operate during a power outage.
Passive systems are defined as those that use no purchased energy to operate, play multiple roles in a building design, and are tightly integrated with the building structure. Before the advent of air-conditioning, passive systems were the norm in building design; window shading, light-colored materials and coatings, insulation, and radiant barriers are all building-level systems that can reduce indoor exposure to temperature.
There is a renewed interest in passive systems because they continue to provide some protective effects during a power outage; this effect is called “passive survivability.” However, while passive systems can moderate interior temperatures, they cannot eliminate heat-related exposure during heat extremes; these systems typically provide conditions that are within a few degrees of the outdoor air temperature.
Because no single strategy is totally effective in reducing exposure to high temperatures, planning for extreme heat events will require addressing high temperatures at all three scales: reducing the urban heat island effect, improving cooling center accessibility, and designing in multiple strategies (in addition to air-conditioning) to ensure that buildings can remain habitable during power outages. Each of these approaches are already discussed by the design community: the challenge will be to make the strategies work together in concert to be prepared for a changing climate.
About the Author
Nicholas B. Rajkovich, PhD, AIA, is an assistant professor at the University at Buffalo in the School of Architecture and Planning. His research investigates adaptation to climate change in cities and buildings. Prior to earning a PhD in Urban and Regional Planning from the University of Michigan, he was a Senior Program Engineer at the Pacific Gas & Electric (PG&E) Company Customer Energy Efficiency Department. Prior to PG&E, Nicholas taught several courses on lighting, acoustics, and building systems in the Department of Architecture at Cornell University. He also worked as an associate at Einhorn Yaffee Prescott in Albany, NY, where he helped architects and engineers reduce the overall environmental impact of buildings under contract to the New York State Energy Research and Development Authority and the U.S. Department of State. He has a Master of Architecture from the University of Oregon and a Bachelor of Architecture from Cornell University.