Spatial Patterns of Heat Vulnerability Constituents across Massachusetts

To address the health threat posed by increasing temperatures, it is necessary to understand where those most vulnerable to heat are located. While an overall heat vulnerability index (HVI) can identify which areas experience the composite burden of vulnerability, we elucidate which component factors drive heterogeneity in heat vulnerability across the state of Massachusetts.

We constructed a Massachusetts HVI which includes factors describing 3 vulnerability dimensions: sociodemographic; environmental/urbanicity; and elderly/social isolation. We calculated the individual HVI components for Massachusetts at the census tract level using data from the American Community Survey and National Land Cover Database at two time points, 2006 and 2011. We linked the HVI to mortality data at the census tract level.

The spatial distribution of the HVI at both time points varied across the state, showing areas of high vulnerability in and around urban areas, as well as in the western part of the state and along Cape Cod.

Census tracts in and around urban areas in the state had highest vulnerability for the sociodemographic component (which included percentage of the population that is Hispanic, Black, with limited English language proficiency, unemployed, below the poverty line, and with a disability), as well as the environmental/urbanicity component (comprised of variables reflecting: housing density; percentage of older homes; open, undeveloped land; high building intensity, and percentage of the population that is foreign born). Vulnerability for the elderly/social isolation component (which included percentage of the population that is ≥65 years old and ≥65 years old and living alone), was high in the western part of the state, as well as along Cape Cod.

In exploring change between time points, we found that 741 of 1439 census tracts experienced an increase in HVI score (indicating increased vulnerability) between 2006 and 2011, while 698 showed a decrease in HVI score.

HVI is multifactorial and the individual contributing factors can differentially vary across large geographical areas. Understanding the individual components of HVI can help us identify necessary sociodemographic, land use, and housing targets for statewide heat vulnerability interventions.