Unraveling the Disparity of Temperature-Mortality Relationship : From Individual to Global Perspectives
Date of Award
Fall 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Forestry and Environmental Studies
First Advisor
Bell, Michelle L.
Abstract
Numerous studies investigating the health impacts of temperature-mortality have consistently demonstrated an increased risk of mortality associated with extreme temperatures. The relationship between temperature and mortality is complex and influenced by various factors, including geography, socio-economic conditions, environmental factors, variations in temperature assessment methods, and differences in health units at individual and country levels. Evaluating and comparing these diverse settings, from local to global perspectives, becomes imperative for optimizing climate change mitigation and adaptation strategies. This dissertation significantly contributes to our understanding of the multifaceted factors that modify the temperature-mortality relationship. By shedding light on these factors, it offers valuable insights to empower communities and policymakers in developing effective methods to mitigate the adverse impacts of climate change.In the first project, Chapter 2 of my research, I focused on investigating the disparities in the temperature-mortality relationship between urban and rural areas. This project was divided into two distinct parts: 1) exploring the temperature-mortality relationship at a county-aggregation level and 2) evaluating the temperature-mortality association at an individual level while comparing the health effects using different exposure assessment methods. For Chapter 2.a, I conducted a comprehensive analysis of North Carolina (NC), USA, examining regional and urban-rural variations in the temperature-mortality association during the period from 2000 to 2016. The overall relative effect for cold-related mortality risk was found to be 1.019 (1.015-1.023), indicating a significant association. Although not statistically significant, urban areas exhibited higher risks for both heat-related (relative effect: 1.006; 95% CI: 0.997-1.016) and cold-related (relative effect: 1.023; 95% CI: 1.017-1.030) mortality compared to rural areas. Similarly, rural areas showed slightly elevated risks for both heat-related (relative effect: 1.002; 95% CI: 0.998-1.017) and cold-related (relative effect: 1.012; 95% CI: 1.001-1.023) mortality. These results indicate the presence of heat- and cold-related mortality risks in North Carolina, with potential variations across different regions, urban-rural areas, and community characteristics. In Chapter 2.b, the second project of my research, I expanded the investigation of urban-rural differences in temperature-mortality relationships at an individual level. I evaluated various methods for estimating temperature exposure using individual-level data and examined their impact on the heat-mortality relationship in North Carolina during the warm months from May to September between 2000 and 2016. The results revealed contrasting outcomes when comparing temperature exposure estimated from monitoring stations versus modeled temperature datasets. Using individual-aggregated monitoring station temperature exposure resulted in higher heat-related mortality risk (odds ratio: 1.29; 95% CI: 1.25, 1.32) when comparing the 99th and 90th temperature percentiles. In contrast, utilizing modeled temperature exposure yielded a lower odds ratio of 1.16 (95% CI: 1.14, 1.17). These findings highlight the influence of different temperature exposure methods on the assessment of temperature-mortality risks. Moving to Chapter 3, the third project, I explored the potential modification of the temperature-mortality relationship by greenspace on a global scale. Analyzing data from 452 cities across 24 countries, I examined the heat-mortality relationship in relation to varying levels of greenspace. Cities with high greenspace demonstrated the lowest heat-mortality relative risk of 1.19 (95% CI: 1.13, 1.25), while cities with low greenspace exhibited a higher heat-related relative risk of 1.46 (95% CI: 1.31, 1.62) when comparing the 99th temperature percentile with the minimum mortality temperature. Furthermore, a 20% increase in greenspace was associated with a 9.02% (95% CI: 8.88, 9.16) decrease in the heat-related attributable fraction, potentially leading to approximately 933 fewer excess deaths per year in the 24 countries studied. These insightful findings offer valuable contributions to future urban planning strategies by emphasizing the integration and prioritization of greenspace within the urban environment. Policymakers and city planners can utilize this information to create sustainable, livable, and healthy cities for future generations. In Chapter 4, the fourth project, I delved into the effect modification of greenspace and impervious surface on the association between heat and mortality, focusing on variations in North Carolina, USA, and how it differs based on race/ethnicity dissimilarity index levels. The analysis revealed that census tracts with low greenspace had a higher heat-mortality relative risk than those with high greenspace (RR comparing risk at the 99th temperature and the minimum mortality temperature: 1.08 (95% CI: 1.02, 1.15) vs. 0.97 (95% CI: 0.87, 1.08)). Similarly, tracts with a high impervious surface exhibited a higher heat-mortality relative risk compared to those with a low impervious surface (1.04 (95% CI: 1.00, 1.09) vs. 0.94 (95% CI: 0.84, 1.05)). Furthermore, census tracts characterized by high dissimilarity values and low greenspace displayed the highest heat-mortality risk in comparison to tracts with high dissimilarity values and high greenspace (1.13 (95% CI: 1.02, 1.24) vs. 0.97 (95% CI: 0.86, 1.09)). These results indicate that communities with low greenspace or high impervious surfaces are associated with higher heat-mortality risks, and this effect modification is more pronounced in regions with high levels of race/ethnicity dissimilarity. These pioneering projects underscore the critical need to comprehensively evaluate the diverse factors that influence the temperature-mortality relationship. The findings unequivocally demonstrate the paramount importance of identifying and understanding these factors to accurately assess their impact on the temperature-mortality association, especially in the context of climate change. These insights carry profound implications for formulating effective strategies to mitigate the health risks posed by rising temperatures, ultimately contributing to the global efforts aimed at combatting climate change and safeguarding public health.
Recommended Citation
Choi, Hayon Michelle, "Unraveling the Disparity of Temperature-Mortality Relationship : From Individual to Global Perspectives" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1219.
https://elischolar.library.yale.edu/gsas_dissertations/1219
