UC San Diego

Background: While the detrimental health effects of extreme heat and wildfire smoke are well established in high-income countries, there is substantially less evidence in low and middle-income settings. This dissertation research aimed to quantify the effects of extreme heat and wildfire smoke through a social vulnerability approach, using the San Diego-Tijuana border as a context to study differential impacts.Methods: This dissertation includes three studies examining the differential impacts of extreme heat and wildfire smoke in a binational context. The first study evaluates the spatial variation in the effect of extreme heat across municipalities in Mexico using a within-community-matched design with a Bayesian Hierarchical model extension and meta-regression to explore socioeconomic drivers. In the second study, we used the San Diego-Tijuana region as a unique context to study the differential effects of wildfire smoke on cardio-respiratory hospitalizations across the border using synthetic control methods (SCM). The third study also used SCM to explore the potential role of wildfire smoke in driving COVID-19 mortality in the San Diego-Tijuana border region. Results: In the first study, we found substantial spatial heterogeneity in the effects of heat across Mexico at the municipality level, and disadvantaged social conditions such as low education, poor housing conditions, and higher marginalization were important predictors of these differences. In the second study, wildfire smoke increased cardio-respiratory hospitalizations in the San Diego-Tijuana border region, with a higher, albeit imprecise, relative change in Tijuana likely driven by a higher poverty rate and increased social vulnerability. Lastly, in the third study, no strong effect of wildfire smoke on COVID-19 mortality was observed in either San Diego or Tijuana. Conclusion: The results of this dissertation indicate that social vulnerability is an important factor in understanding the health risks of extreme heat and wildfire smoke. We hope that highlighting the differential susceptibility of populations to these effects can help inform binational efforts to protect those that are most vulnerable to extreme weather events which will be increasingly prevalent and severe in the context of climate change.