Date Published: June 25, 2014
Publisher: Public Library of Science
Author(s): Brian Stone, Jason Vargo, Peng Liu, Dana Habeeb, Anthony DeLucia, Marcus Trail, Yongtao Hu, Armistead Russell, Igor Linkov.
Heat-related mortality in US cities is expected to more than double by the mid-to-late 21st century. Rising heat exposure in cities is projected to result from: 1) climate forcings from changing global atmospheric composition; and 2) local land surface characteristics responsible for the urban heat island effect. The extent to which heat management strategies designed to lessen the urban heat island effect could offset future heat-related mortality remains unexplored in the literature. Using coupled global and regional climate models with a human health effects model, we estimate changes in the number of heat-related deaths in 2050 resulting from modifications to vegetative cover and surface albedo across three climatically and demographically diverse US metropolitan areas: Atlanta, Georgia, Philadelphia, Pennsylvania, and Phoenix, Arizona. Employing separate health impact functions for average warm season and heat wave conditions in 2050, we find combinations of vegetation and albedo enhancement to offset projected increases in heat-related mortality by 40 to 99% across the three metropolitan regions. These results demonstrate the potential for extensive land surface changes in cities to provide adaptive benefits to urban populations at risk for rising heat exposure with climate change.
Human health effects associated with rising temperatures are expected to increase significantly by mid-to-late century. A large body of work now estimates an increase in mean global temperature from pre-industrial averages of more than 2°C by late century under mid-range emissions scenarios . A smaller but growing body of work has sought to estimate the effects of projected warming on heat-related mortality. Employing health impact functions derived from epidemiological studies of historical warm season mortality rates, recent work projects an increase in annual heat-related mortality of between 3,500 and 27,000 deaths in the United States by mid-century . Studies focused on individual cities estimate an increase in annual heat-related mortality by a factor of 2 to 7 by the mid-to-late 21st century –.
Temperature change was first modeled for the 2050 BAU scenario in reference to base year (2010) conditions in each metropolitan region. Three measures of temperature change were derived for each MSA to correspond with the HRFs used to assess health outcomes, including average temperature (AvgT), average apparent temperature (AvgapT), and minimum temperature (MinT). Under the BAU scenario, warm season temperatures increase from base year temperatures by an average of 1.2°C in the Atlanta and Philadelphia MSAs, and by an average 2.2°C in the Phoenix MSA (see Figure 1, bottom panel).
The results of our study support climate adaptation strategies designed to lessen the risk of heat exposure through mitigation of the urban heat island effect. Heat management strategies were found to be effective in offsetting mortality during both heat wave and non-heat wave conditions. Our results suggest that measures of relative risk for heat-related mortality based on average warm season temperatures only may significantly underestimate the potential for heat deaths during extreme heat events spanning two or more days. When accounting for both average warm season and heat wave conditions, the estimated number of avoided deaths due to the various heat management strategies was found to be 33% higher, on average, than model runs responsive to average warm season temperatures only.
We examined the potential for urban heat management strategies to offset projected increases in heat-related mortality in three large US metropolitan regions by mid-century using a set of global/regional climate and human health effects models. Variable combinations of heat management strategies involving vegetation and albedo enhancement were estimated to offset projected heat-related mortality by a range of 40 to 99%, depending on the metropolitan region and health impact function applied. These results highlight the potential for extensive land surface changes in cities to provide adaptive benefits to urban populations at risk for rising heat exposure with climate change.