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Dissertation
Beyond the flood and flames: exploring health impacts of climate-exacerbated disasters
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2025
DOI: 10.25820/etd.007845
Abstract
Climate-exacerbated disasters, such as hurricanes and wildfires, are associated with a wide range of adverse health effects in the general population and are increasing in frequency and severity due to global climate change. Due to prior military exposures and distinct sociodemographic characteristics, U.S. veterans may be more vulnerable to negative health impacts of climate-exacerbated disasters than the general population. The objective of this dissertation is to determine whether exposure to climate-exacerbated disasters are associated with mental health, respiratory, and cardiovascular events among U.S. veterans.
These studies are retrospective cohort studies that consist of U.S. veterans enrolled in Veteran Health Association (VHA) primary care and whose home addresses were in regions that were affected by Hurricanes Sandy or Harvey, or the Camp and Woolsey Fires. The hurricane analyses included data from 960,394 veterans between 2011-2016 in the Sandy cohort and from 795,746 veterans between 2016-2021 in the Harvey cohort. Affected regions were determined from Federal Emergency Management Agency designations; patient-level clinical data were obtained through VHA electronic health records. The outcomes of interest were acute care mental health, respiratory or cardiovascular events (RE/CVE), which included urgent care/emergency department visits (UC/ED) or in-patient admissions. The association between the outcome and exposure to the hurricane was estimated using Cox regression models with adjustments for multiple demographic and neighborhood characteristics and accounting for pre-existing regional differences.
The wildfire analyses included data from 991,861 veterans between November 8 and November 26, 2018. PM2.5 exposure was determined through a machine-learning downscaled air pollution model and patient-level clinical data were obtained through VHA electronic health records. Outcomes of interest included UC/ED visits or in-patient admissions where the primary diagnosis was asthma, chronic obstructive pulmonary disease, respiratory infection, myocardial infarction, heart failure, or stroke. Cox regression models with a time-dependent covariate for PM2.5 (lag-day 1) were used to estimate the hazard ratio (HR) between elevated levels of PM2.5 and our outcomes of interest.
For both hurricane cohorts, increasing neighborhood disadvantage was associated with an increased hazard of having a subsequent acute care mental health visit. This effect was more pronounced in healthier veterans [1-year Sandy HR = 1.62 (95% confidence interval 1.53-1.71); 1-year Harvey HR = 1.64 (1.54-1.74)] compared to sicker veterans [Sandy HR = 1.22 (1.17-1.26); Harvey HR = 1.21 (1.13-1.30)]. Importantly, after adjusting for pre-existing differences, the association between hurricane exposure and acute care mental health visits were largely null. Increasing neighborhood disadvantage was associated with an increased hazard of having a subsequent mental health visit or CVE/RE in both cohorts. This effect was more pronounced in healthier veterans compared to sicker veterans. Comparing the flooded with individual assistance region to the unexposed region among the healthier veterans in the Harvey cohort, the post-hurricane hazard ratio of REs increased by 15 percent from the pre-hurricane level.
During the wildfire period, PM2.5 exposure ranged from 0.36 to 380 μg/m3. High PM2.5 exposure (PM2.5 > 55.4 μg/m3) was associated with a HR of 1.37 (1.10-1.70), 3.88 (2.38-6.32), and 1.85 (1.40-2.44) for all REs, asthma, and COPD, respectively, among healthier veterans. Among sicker veterans, high PM2.5 exposure was associated with a HR of 1.71 (1.02-2.87) and 1.42 (1.05-1.91) for asthma and respiratory infections, respectively. Results for cardiovascular events were inconsistent and mostly null, with the exception of stroke among sicker veterans for those with high levels of PM2.5 exposure, HR of 1.54 (1.02-2.32). Increasing neighborhood disadvantage was associated with increasing HR for all RE/CVE, except asthma, among healthier veterans. Among sicker veterans, neighborhood disadvantage did not have a consistent effect on health outcomes. While there was no clear association between advanced age (≥65 years) and respiratory outcomes, age was associated with increased HRs for all CVE and the specific cardiovascular endpoints.
In conclusion, this research utilized a novel and highly granular approach to examine the impacts of hurricanes and wildfires on morbidity among U.S. veterans. These findings are the first to show that hurricane exposure was not associated with adverse mental health outcomes among U.S. veterans and illustrated the importance of considering pre-existing regional differences when assessing the impacts of hurricanes. Our results indicate that neighborhood characteristics are the dominant determinants of adverse health outcomes rather than exposure to a hurricane.
The findings from the Camp and Woolsey Fires analysis show that PM2.5 exposure among U.S. veterans is strongly associated with adverse respiratory outcomes, especially exacerbations of asthma and COPD; association between PM2.5 exposure and cardiovascular events was less clear. It also shows the importance of considering prior health status, as that may modify the impacts PM2.5 exposure has among different populations. As climate change continues to worsen the impacts of hurricanes and wildfires in the U.S., it is important that we deepen our understanding of the health burdens and identify communities most vulnerable to their effects.
Details
- Title: Subtitle
- Beyond the flood and flames: exploring health impacts of climate-exacerbated disasters
- Creators
- Caryn Stacie Yip
- Contributors
- Peter S Thorne (Advisor)Margaret Carrel (Committee Member)Michael P Jones (Committee Member)Peter J Kaboli (Committee Member)Jerald L Schnoor (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Occupational and Environmental Health
- Date degree season
- Spring 2025
- DOI
- 10.25820/etd.007845
- Publisher
- University of Iowa
- Number of pages
- xiv, 112 pages
- Copyright
- Copyright 2025 Caryn Stacie Yip
- Language
- English
- Date submitted
- 04/24/2025
- Description illustrations
- illustrations, tables, graphs, maps
- Description bibliographic
- Includes bibliographical references (pages 77-89).
- Public Abstract (ETD)
- Hurricanes and wildfires are associated with a wide range of adverse health effects in the general population and are increasing in frequency and severity due to global climate change. U.S. veterans may be more vulnerable to negative health impacts of these disasters than the general population. The goal of this dissertation is to determine whether exposure to these disasters are associated with mental health, respiratory, and cardiovascular events among U.S. veterans. This study revealed that after accounting for pre-existing regional differences, hurricane exposure had little effect on adverse health outcomes among U.S. veterans. This study also found that exposure to elevated levels of air pollution during a wildfire event were associated with increased respiratory problems among this population, especially among healthier veterans. During both hurricanes and wildfires, neighborhood disadvantage was associated with adverse health outcomes. This dissertation illustrates the importance of considering pre-existing differences, neighborhood disadvantage, and prior health status when evaluating how veterans experience these disasters. As climate change continues to alter hurricane and wildfire behavior, it is important that scientists, researchers, and policymakers understand the health burden associated with these disasters and which communities are most vulnerable.
- Academic Unit
- Occupational and Environmental Health
- Record Identifier
- 9984830727902771
Metrics
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