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Colleen E. Reid,^1,* Marie S. O’Neill,² Carina J. Gronlund,² Shannon J. Brines,³ Daniel G. Brown,³ Ana V. Diez-Roux,² and Joel Schwartz⁴

¹Environmental Health Sciences Division, School of Public Health, University of California at Berkeley, California, USA; ²School of Public Health, and ³School of Natural Resources and the Environment, University of Michigan, Ann Arbor, Michigan, USA; ⁴Harvard University School of Public Health, Boston, Massachusetts, USA

Abstract
Background: The evidence that heat waves can result in both increased deaths and illness is substantial, and concern over this issue is rising because of climate change. Adverse health impacts from heat waves can be avoided, and epidemiologic studies have identified specific population and community characteristics that mark vulnerability to heat waves.

Objectives: We situated vulnerability to heat in geographic space and identified potential areas for intervention and further research.

Methods: We mapped and analyzed 10 vulnerability factors for heat-related morbidity/mortality in the United States: six demographic characteristics and two household air conditioning variables from the U.S. Census Bureau, vegetation cover from satellite images, and diabetes prevalence from a national survey. We performed a factor analysis of these 10 variables and assigned values of increasing vulnerability for the four resulting factors to each of 39,794 census tracts. We added the four factor scores to obtain a cumulative heat vulnerability index value.

Results: Four factors explained > 75% of the total variance in the original 10 vulnerability variables: a) social/environmental vulnerability (combined education/poverty/race/green space) , b) social isolation, c) air conditioning prevalence, and d) proportion elderly/diabetes. We found substantial spatial variability of heat vulnerability nationally, with generally higher vulnerability in the Northeast and Pacific Coast and the lowest in the Southeast. In urban areas, inner cities showed the highest vulnerability to heat.

Conclusions: These methods provide a template for making local and regional heat vulnerability maps. After validation using health outcome data, interventions can be targeted at the most vulnerable populations.

Key words: climate, environmental health, geographic information systems, heat, public health, vulnerable populations. Environ Health Perspect 117:1730–1736 (2009) . doi:10.1289/ehp.0900683 available via http://dx.doi.org/ [Online 10 June 2009]

Address correspondence to C. Reid, Environmental Health Sciences Division, School of Public Health, University of California at Berkeley, 50 University Hall #7360, Berkely, CA 94720-7360, USA. Telephone: 510-643-9257. Fax: 510-642-5815. E-mail: creid@berkeley.edu

*C.E.R was an Association of Schools of Public Health Environmental Health Fellow at U.S. Environmental Protection Agency when this work was done.

We thank J. Yanosky for sharing green space data.

This article was developed partially under cooperative agreements X3-83085001 and X3-83388101 awarded by the U.S. Environmental Protection Agency (EPA) to the Association of Schools of Public Health and partially under the U.S. EPA Science to Achieve Results (STAR) Program grant R832752010.

The views expressed in this article are solely those of the authors and do not necessarily reflect those of the U.S. EPA, nor does the U.S. EPA endorse any products or commercial services mentioned in this publication.

The authors declare they have no competing financial interests.

Received 12 February 2009 ; accepted 10 June 2009.