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Redefining the urban heat island Stewart, Iain Douglas

Abstract

The effect of urban development on local thermal climate is ostensibly well documented in scientific literature. Since the nineteenth century, observations of “urban-rural” air temperature differences (ΔTu­-r), or urban heat island magnitudes, have been reported for hundreds of cities worldwide. The historical and geographical scope of the heat island literature is impressive. Over time, however, methodologists have raised concerns about the rigor and authenticity of that literature, especially regarding the definition, measurement, and reporting of heat island magnitudes. Indiscriminate use of “urban” and “rural” by heat island investigators to describe their field sites is a particular concern. Much confusion now surrounds the physical and cultural characteristics of so-called urban and rural sites in heat island literature. This thesis confronts these concerns through two approaches. The first approach synthesizes and evaluates a sample of 190 observational heat island studies from the period 1950 to 2007. The synthesis uses nine criteria of scientific method and communication to critically assess the experimental quality of each study. Results are discouraging: the mean quality score of the literature sample is just 50 percent, and nearly one-half of the reported heat island magnitudes are judged to be scientifically indefensible on account of incomplete or incompetent reporting. The second approach develops a landscape classification system to standardize reporting of heat island field sites and temperatures in all cities. The local climate zone (LCZ) system comprises 17 zones and is the first comprehensive climate-based classification of urban and rural landscapes for heat island investigators. Each zone represents an area that is local in scale and unique in land cover, building morphology, and screen-level thermal climate. Results show that the new classification leads to a more purposeful interpretation of heat island magnitude as ΔTLCZ, and thereby constrains the operational use of ΔTu­-r to climatologically defined and universally recognized urban and rural zones. The thesis concludes with a conceptual typology of urban heat island magnitudes, and a list of specific guidelines and recommendations to improve methodology and communication in heat island studies.

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Attribution-NonCommercial-NoDerivs 3.0 Unported

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