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Edited by Susan Hanson, Clark University, Worcester, MA, and approved July 6, 2020 (received for review March 23, 2020)
Significance
We present climate projections of population-weighted heat and cold exposure that directly and simultaneously account for greenhouse gas (GHG) and urban development-induced warming. Previous population heat and cold exposure estimates have not accounted for urban development-induced climate impacts, have neglected interactions between urban development-induced warming and GHG-induced climate change, and have used fixed temperature thresholds that may be inappropriate for some cities. We develop a more detailed and nuanced definition of extreme heat and cold exposure through key innovations, and our predicted exposure is substantially greater than previous assessments. Our results demonstrate that Sunbelt cities are projected to undergo the largest relative increase in population heat exposure to locally defined extreme heat conditions during the 21st century.
Abstract
We use a suite of decadal-length regional climate simulations to quantify potential changes in population-weighted heat and cold exposure in 47 US metropolitan regions during the 21st century. Our results show that population-weighted exposure to locally defined extreme heat (i.e., “population heat exposure”) would increase by a factor of 12.7–29.5 under a high-intensity greenhouse gas (GHG) emissions and urban development pathway. Additionally, end-of-century population cold exposure is projected to rise by a factor of 1.3–2.2, relative to start-of-century population cold exposure. We identify specific metropolitan regions in which population heat exposure would increase most markedly and characterize the relative significance of various drivers responsible for this increase. The largest absolute changes in population heat exposure during the 21st century are projected to occur in major US metropolitan regions like New York City (NY), Los Angeles (CA), Atlanta (GA), and Washington DC. The largest relative changes in population heat exposure (i.e., changes relative to start-of-century) are projected to occur in rapidly growing cities across the US Sunbelt, for example Orlando (FL), Austin (TX), Miami (FL), and Atlanta. The surge in population heat exposure across the Sunbelt is driven by concurrent GHG-induced warming and population growth which, in tandem, could strongly compound population heat exposure. Our simulations provide initial guidance to inform the prioritization of urban climate adaptation measures and policy.
Footnotes
- ↵1To whom correspondence may be addressed. Email: ashley.broadbent{at}asu.edu or Matei.Georgescu{at}asu.edu.
Author contributions: A.M.B., E.S.K., and M.G. designed research; A.M.B. and E.S.K. performed research; A.M.B. analyzed data; and A.M.B., E.S.K., and M.G. wrote the paper.
The authors declare no competing interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2005492117/-/DCSupplemental.
Data Availability.
Regional climate simulation output data used in this study are accessible at https://erams.com/public_data/climate#wrf_asu (36). Population heat and cold exposure data are available upon reasonable request.
Published under the PNAS license.
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The motley drivers of heat and cold exposure in 21st century US cities
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- Physical Sciences
- Earth, Atmospheric, and Planetary Sciences
- Sustainability Science
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