Interactions between urban heat islands and heat waves

Journal Article · 16 February 2018 · Environmental Research Letters

DOI: https://doi.org/10.1088/1748-9326/aa9f73 · OSTI ID:1485083

Zhao, Lei  ^[1]; Oppenheimer, Michael ^[2]; Zhu, Qing ^[3]; Baldwin, Jane W. ^[4]; Ebi, Kristie L.  ^[5]; Bou-Zeid, Elie ^[6]; Guan, Kaiyu  ^[7]; Liu, Xu ^[8]

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1. Princeton Univ., NJ (United States). Program in Science, Technology and Environmental Policy (STEP)
2. Princeton Univ., NJ (United States). Woodrow Wilson School of Public and International Affairs and Dept. of Geosciences
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Climate and Ecosystem Sciences Division, Climate Sciences Dept.
4. Princeton Univ., NJ (United States). Program in Atmospheric and Oceanic Sciences (AOS)
5. Univ. of Washington, Seattle, WA (United States). Dept. of Global Health
6. Princeton Univ., NJ (United States). Dept. of Civil and Environmental Engineering
7. Univ. of Illinois, Urbana-Champaign, IL (United States). Dept. of Natural Resources and Environmental Sciences and National Center for Supercomputing Applications
8. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). International Energy Analysis Dept., China Energy Group

Heat waves (HWs) are among the most damaging climate extremes to human society. Climate models consistently project that HW frequency, severity, and duration will increase markedly over this century. For urban residents, the urban heat island (UHI) effect further exacerbates the heat stress resulting from HWs. Here we use a climate model to investigate the interactions between the UHI and HWs in 50 cities in the United States under current climate and future warming scenarios. We examine UHI_2m (defined as urban-rural difference in 2m-height air temperature) and UHI_s (defined as urban-rural difference in radiative surface temperature). Our results show significant sensitivity of the interaction between UHI and HWs to local background climate and warming scenarios. Sensitivity also differs between daytime and nighttime. During daytime, cities in the temperate climate region show significant synergistic effects between UHI and HWs in current climate, with an average of 0.4 K higher UHI_2m or 2.8 K higher UHI_s during HWs than during normal days. These synergistic effects, however, diminish in future warmer climates. In contrast, the daytime synergistic effects for cities in dry regions are insignificant in the current climate, but emerge in future climates. At night, the synergistic effects are similar across climate regions in the current climate, and are stronger in future climate scenarios. We use a biophysical factorization method to disentangle the mechanisms behind the interactions between UHI and HWs that explain the spatial-temporal patterns of the interactions. Results show that the difference in the increase of urban versus rural evaporation and enhanced anthropogenic heat emissions (air conditioning energy use) during HWs are key contributors to the synergistic effects during daytime. The contrast in water availability between urban and rural land plays an important role in determining the contribution of evaporation. At night, the enhanced release of stored and anthropogenic heat during HWs are the primary contributors to the synergistic effects.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1485083
• Journal Information: Environmental Research Letters, Vol. 13, Issue 3; ISSN 1748-9326
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English