Urban heat inequities in the United States: a scoping review

Abstract

Extreme heat is a major public health concern, as cities are experiencing rising temperatures, with certain populations disproportionately exposed to high temperatures. A growing body of research has assessed inequities in the distribution of urban heat across population groups; however, this area has not yet been specifically reviewed. Thus, we conduct a scoping review of studies associating urban heat exposures with sociodemographic factors in the United States to provide an overview of the state of the literature. Of the 1381 unique studies identified from two academic search systems, 75 peer-reviewed studies that fit the eligibility criteria were included in the review. These studies were qualitatively summarized based on their geographic coverage, heat and sociodemographic indicators, analytical approaches, and overall findings. Most studies (65%) examined variations in urban heat using land surface temperatures. The most reported sociodemographic categories were income-related measures (81%) and race and ethnicity (72%). At least 11 different types of generalized statistical methods were used to investigate the association between urban heat and sociodemographic indicators, such as t-test (or non-parametric equivalent), cluster analysis, regression analysis etc. Nearly half of the studies (48%) analyzed these associations at the census tract level. Urban heat inequities were the sole focus in only 19% of studies and were studied as either a primary (64%) or secondary (17%) component in combination with other environmental and/or health factors. The review illustrated the spatial distribution of studied locations across cities, counties, metro areas, states, and climate zones, and identified the most represented geographic areas in the literature as New York City, Philadelphia, Phoenix metro area, California, Texas and the Northeast region. Most studied cities were concentrated in cold climate zones followed by the mixed-humid zone. The resulting database of existing literature developed by this scoping review can support future research by guiding the selection of study areas, indicators, and heat inequity analytic methods. The review also highlights the need for further longitudinal investigations that account for historical segregation for a more complete understanding of urban heat inequities.