Title: Evaluating the impact of the urban heat island on public health
Description: Increased rates of mortality and morbidity due to summertime heat are a significant problem in New York City (NYC) and for many cities around the world, and are expected to increase with a warming climate. An ecologic design was used to evaluate the association between neighborhood scale characteristics (socioeconomic/demographic, the built and biophysical environment, health status and risk behaviors) and senior citizen's mortality rates during heat events in New York City. As a measure of relative vulnerability to heat, this analysis used the natural cause mortality rate ratio among those aged 65+ (MRR65+), comparing extremely hot days (maximum heat index 100+) to other warm season days. Data were pooled across the years 1997-2006. The relationship between intra-urban microclimates and the risk of heat-related mortality was assessed through Landsat-derived surface temperatures averaged to the neighborhood scale. Excess mortality during heat event days was unevenly distributed in NYC's Community Districts and United Hospital Fund (UHF) areas during 1997-2006, with higher rates of excess deaths in parts of southwestern Bronx, northern Manhattan, central Brooklyn and the eastern side of midtown Manhattan.

Some areas, including parts of northern Staten Island, northern and southeastern Queens, and the Upper West Side of Manhattan had lower rates of mortality on heat alert days during this time period (MRR65+ < 1.0) compared to the average summer season day. Significant positive associations were found between heat-mortality rates and characteristics at the neighborhood level: poor housing conditions, poverty, impervious land cover, senior's hypertension and the surface temperatures aggregated to the UHF area level during the warm season. A negative association between area-based home-ownership rates and the mortality rate ratio was the strongest correlation found in the study. Several measures of housing quality were significantly correlated with the MRR65+, including rates of dilapidated buildings and property tax delinquencies, suggesting that the quality of senior's housing is a population-level risk factor for premature heat-associated mortality. Senior's air condition access was negatively correlated with the mortality rate ratio.

The lowest-income areas had a trend towards higher heat-associated mortality rates. Low-income areas also had a trend towards hotter surface temperatures and a lower degree of air conditioning access for senior citizens. The hottest Districts and UHF-areas generally had higher mortality rate ratios; however, stratification by poverty rates and income levels showed this trend existed for the low-income/higher poverty neighborhoods, but not for high-income/low poverty areas. Percent Black/African American and percent poverty by UHF-area were strong negative predictors of senior's air conditioning access in multivariate regression. In multivariate models, NYC's surface urban heat island is strongly associated with impervious cover and poverty rates. There is a trend for an increasing mortality rate ratio for areas with the least proportion of White population. These findings suggest that redistributive policies to improve the housing conditions of elderly residents could play a role in reducing heat-related mortality in New York City, although these policies are not yet explicitly considered as part of climate adaptive planning.

Urban heat island mitigation programs that address economic disparities and incorporate local knowledge on neighborhood characteristics may be the most effective in reducing the health impacts of climate extremes and variability. Towards that end, a community-based adaptation planning process may help address the social justice dimension of the impacts of extreme events and climate change in New York City while increasing the effectiveness of adaptive programs and policies.