Publication Date:
2014-07-11
Description:
The urban heat island (UHI), a common phenomenon in which surface temperatures are higher in urban areas than in surrounding rural areas, represents one of the most significant human-induced changes to Earth's surface climate. Even though they are localized hotspots in the landscape, UHIs have a profound impact on the lives of urban residents, who comprise more than half of the world's population. A barrier to UHI mitigation is the lack of quantitative attribution of the various contributions to UHI intensity (expressed as the temperature difference between urban and rural areas, DeltaT). A common perception is that reduction in evaporative cooling in urban land is the dominant driver of DeltaT (ref. 5). Here we use a climate model to show that, for cities across North America, geographic variations in daytime DeltaT are largely explained by variations in the efficiency with which urban and rural areas convect heat to the lower atmosphere. If urban areas are aerodynamically smoother than surrounding rural areas, urban heat dissipation is relatively less efficient and urban warming occurs (and vice versa). This convection effect depends on the local background climate, increasing daytime DeltaT by 3.0 +/- 0.3 kelvin (mean and standard error) in humid climates but decreasing DeltaT by 1.5 +/- 0.2 kelvin in dry climates. In the humid eastern United States, there is evidence of higher DeltaT in drier years. These relationships imply that UHIs will exacerbate heatwave stress on human health in wet climates where high temperature effects are already compounded by high air humidity and in drier years when positive temperature anomalies may be reinforced by a precipitation-temperature feedback. Our results support albedo management as a viable means of reducing DeltaT on large scales.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhao, Lei -- Lee, Xuhui -- Smith, Ronald B -- Oleson, Keith -- England -- Nature. 2014 Jul 10;511(7508):216-9. doi: 10.1038/nature13462.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉1] Yale-NUIST Center on Atmospheric Environment, Nanjing University of Information Science and Technology, Nanjing 210044, China [2] School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA. ; Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06511, USA. ; National Center for Atmospheric Research, Boulder, Colorado 80305, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25008529" target="_blank"〉PubMed〈/a〉
Keywords:
*Cities
;
*Climate
;
Environmental Monitoring
;
*Hot Temperature
;
Humans
;
Humidity
;
*Models, Theoretical
;
North America
;
Population Density
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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