Towards More Comprehensive Projections of Urban Heat-Related Mortality: Estimates for New York City under Multiple Population, Adaptation, and Climate Scenarios

Abstract

Background: High temperatures have substantial impacts on mortality and, with growing concerns about climate change, numerous studies have developed projections of future heat-related deaths around the world. Projections of temperature-related mortality are often limited by insufficient information to formulate hypotheses about population sensitivity to high temperatures and future demographics.

Objectives: The present study derived projections of temperature-related mortality in New York City by taking into account future patterns of adaptation or demographic change, both of which can have profound influences on future health burdens.

Methods: We adopted a novel approach to modeling heat adaptation by incorporating an analysis of the observed population response to heat in New York City over the course of eight decades. This approach projected heat-related mortality until the end of the 21st century based on observed trends in adaptation over a substantial portion of the 20th century. In addition, we incorporated a range of new scenarios for population change until the end of the 21st century. We then estimated future heat-related deaths in New York City by combining the changing temperature-mortality relationship and population scenarios with downscaled temperature projections from the 33 global climate models (GCMs) and two Representative Concentration Pathways (RCPs).

Results: The median number of projected annual heat-related deaths across the 33 GCMs varied greatly by RCP and adaptation and population change scenario, ranging from 167 to 3,331 in the 2080s compared with 638 heat-related deaths annually between 2000 and 2006.

Conclusions: These findings provide a more complete picture of the range of potential future heat-related mortality risks across the 21st century in New York City, and they highlight the importance of both demographic change and adaptation responses in modifying future risks. Citation: Petkova EP, Vink JK, Horton RM, Gasparrini A, Bader DA, Francis JD, Kinney PL. 2017. Towards more comprehensive projections of urban heat-related mortality: estimates for New York City under multiple population, adaptation, and climate scenarios. Environ Health Perspect 125:47-55; http://dx.doi.org/10.1289/EHP166.

Figure 1

Temperature-specific mortality curves for New York City, 1900–2100. (A) Adaptation model assumes that temperature-specific relative risks will decrease by an additional 20% (“low adaptation”) between 2010 and 2100 compared with the 2000s. (B) Adaptation model assumes that temperature-specific relative risks will decrease by an additional 80% (“high adaptation”) between 2010 and 2100 compared with the 2000s. Points represent the relative risks (RRs) calculated using the distributed lag non-linear model (DLNM) for each temperature for the 1970s (1973–1979), 1980s (1980–1989), 1990s (1990–1999), and 2000s (2000–2006). RRs were calculated for June–September using a model with a quadratic spline with 4 degrees of freedom and 22°C as a reference temperature.

Figure 2

New York City (NYC) population by 2100 calculated according to the five population scenarios developed for this study. “Baseline” assumed that all parameters of the model remain constant; that is, age-specific fertility and mortality rates and age characteristics of migration are all kept constant, but the population ages forward. “Decreased mortality” assumed a decrease in age-specific mortality rates such that the values reach 2/3 of the 2010 values by 2100. “Increased in-migration” assumed that the growth of domestic in-migration (from other parts of the United States to New York City) will be half of the growth of the U.S. population and that the growth of international in-migration (from outside of the United States to New York City) will be half of the growth of the projected international in-migration nationwide. “Increased out-migration”: assumed that the rate of out-migration would increase by 25% over the projection period. “Constant” assumed that the population and the age of the population remain constant at 2010 levels.

Figure 3

Median annual projected heat-related deaths in New York City according to two Representative Concentration Pathways (RCPs), (A) RCP4.5 and (B) RCP8.5, and across 33 global climate models (GCMs) during the 2020s (2010–2039), the 2050s (2040–2069), and the 2080s (2070–2099). The corresponding numeric data are provided in Table 2. Heat adaptation scenarios are indicated by circle size and include “high adaptation,”whereadaptation, as measured by the minimal relative risk for a given temperature to be reached by the year 2100 (RR_min), is projected to reach a value 80% lower than the RR calculated at each degree Celsius (°C) during the 2000s; “low adaptation,” where adaptation, as measured by RR_min, is projected to reach a value 20% lower than the RR calculated at each degree Celsius (°C) during the 2000s; and “no adaptation,” wherein future adaptation does not occur and adaptation, as measured by RR_min, remains the same as the RR calculated at each degree Celsius (°C) during the 2000s. Population scenarios are indicated by color and included “baseline,” which assumed that all parameters of the model remain constant; that is, age-specific fertility and mortality rates and age characteristics of migration are all kept constant, but the population ages forward; “decreased mortality,” which assumed a decrease in age-specific mortality rates such that the values reach 2/3 of the 2010 values by 2100; “increased in-migration,” which assumed that the growth of domestic in-migration (from other parts of the United States to New York City) will be half of the growth of the U.S. population and that the growth of international in-migration (from outside of the United States to New York City) will be half of the growth of the projected international in-migration nationwide; “increased out-migration,”which assumed that the rate of out-migration would increase by 25% over the projection period; and “constant,” which assumed that the population and the age of the population remain constant at 2010 levels. For reference, there were 638 heat-related deaths annually between 2000 and 2006.