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Open AccessArticle

Heat and Humidity in the City: Neighborhood Heat Index Variability in a Mid-Sized City in the Southeastern United States

Department of Geography, The University of Tennessee, 304 Burchfiel Geography Building, Knoxville, TN 37996, USA
College of Social Work, The University of Tennessee, 408 Henson Hall, Knoxville, TN 37996, USA
Department of Civil and Environmental Engineering, The University of Tennessee, 325 John D. Tickle Building, Knoxville, TN 37996, USA
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Academic Editors: P. Grady Dixon and Scott C. Sheridan
Int. J. Environ. Res. Public Health 2016, 13(1), 117;
Received: 1 October 2015 / Revised: 17 December 2015 / Accepted: 6 January 2016 / Published: 11 January 2016
Daily weather conditions for an entire city are usually represented by a single weather station, often located at a nearby airport. This resolution of atmospheric data fails to recognize the microscale climatic variability associated with land use decisions across and within urban neighborhoods. This study uses heat index, a measure of the combined effects of temperature and humidity, to assess the variability of heat exposure from ten weather stations across four urban neighborhoods and two control locations (downtown and in a nearby nature center) in Knoxville, Tennessee, USA. Results suggest that trees may negate a portion of excess urban heat, but are also associated with greater humidity. As a result, the heat index of locations with more trees is significantly higher than downtown and areas with fewer trees. Trees may also reduce heat stress by shading individuals from incoming radiation, though this is not considered in this study. Greater amounts of impervious surfaces correspond with reduced evapotranspiration and greater runoff, in terms of overall mass balance, leading to a higher temperature, but lower relative humidity. Heat index and relative humidity were found to significantly vary between locations with different tree cover and neighborhood characteristics for the full study time period as well as for the top 10% of heat index days. This work demonstrates the need for high-resolution climate data and the use of additional measures beyond temperature to understand urban neighborhood exposure to extreme heat, and expresses the importance of considering vulnerability differences among residents when analyzing neighborhood-scale impacts. View Full-Text
Keywords: urban heat island; heat exposure; microclimate; impervious surface; canopy urban heat island; heat exposure; microclimate; impervious surface; canopy
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Hass, A.L.; Ellis, K.N.; Reyes Mason, L.; Hathaway, J.M.; Howe, D.A. Heat and Humidity in the City: Neighborhood Heat Index Variability in a Mid-Sized City in the Southeastern United States. Int. J. Environ. Res. Public Health 2016, 13, 117.

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