Over the past several decades, more frequent and intense extreme heat events have been an increasing threat to human health and economic performance. These extreme heat events result in more fatalities than all other types of extreme weather events, as well as a series of clinical syndromes and chronic diseases, which may expose those with underlying health problems to higher mortality risks. At the same time, extreme heat increases wildfire risks. In recent decades, the United States (U.S.) has experienced upward trends in total acreages burned by wildfires and the average size of wildfires. These trends are expected to grow with the changing climate and as more households move to the wildland-urban interface (WUI). Wildfires can lead to direct injuries and fatalities as well as direct damage to properties and infrastructures. Also, wildfires can lead to environmental changes in many ecosystems. The burning of biomass and soil-based organic matter can generate a large amount of haze and smoke composed primarily of fine particulate matter (PM2.5), which is another threat in and of itself but also because it exacerbates the impacts of extreme heat, influences economic development patterns, and interferes with the enjoyment of environmental goods and services directly or indirectly.Based on the evidence of the inter-relatedness of heat and air pollution and the health risks of heat and air pollution, the first chapter provides nationally representative, robust, and precise estimates of the joint impacts of heat and PM2.5 on mortality in the U.S. The chapter employs a county-year balanced panel dataset covering 2,992 U.S. counties from 2001 through 2011 and applies a Fixed-effect Poisson model. I correct the endogeneity of PM2.5 by applying the control function approach and exploring transboundary externalities of all-source and wildfire-caused PM2.5. I find that the heat index and PM2.5 are positively and significantly associated with all mortalities. PM2.5 is a positive confounder of heat and vice versa. Failure to consider the endogeneity of PM2.5 leads to a substantial underestimation of PM2.5 risk. The overestimation bias caused by ignoring the potential confounding effect between heat and PM2.5 is magnified once the endogeneity of PM2.5 is further addressed. My evaluation also offers evidence of the spillover effects of both PM2.5 and wildfires.Wildfires affect human health directly and indirectly via the environmental (dis)amenities induced by wildfires. The second chapter employs the same dataset and further explores the mechanisms by which wildfires affect human health by examining the extent of the direct and indirect health impacts by applying a mediation analysis. In particular, it focuses on the air pollution (PM2.5) channel. It finds that complementary mediations exist for all-cause, respiratory system disease, and circulatory system disease mortality, and the indirect impacts of wildfires through PM2.5 account for 58%, 47%, and 21% of the total effects of wildfires, respectively. I do not find evidence of a mediation effect through PM2.5 for suicide, but the result suggests a potential delayed direct impact of wildfires on suicide. In addition, the analysis suggests that the spillover effect of wildfires is substantially larger than the local wildfire effect. Although most previous studies assume that wildfires are exogenous, this study finds that failing to consider the causes of wildfires will lead to upwardly biased estimates of health impacts.The last chapter conducts a non-market valuation of the impact of wildfires and wildfire-induced PM2.5 on the housing market by applying a hedonic price model and mediation analysis approach. This study also explores the potential reasons why more people choose to move in or near the wildland-urban interface (WUI). In particular, I examine the degree to which people may underestimate wildfire risks and the tradeoff between the enjoyment of natural resources and increased wildfire risks. I employ a nationwide repeat-sale dataset between 2010 and 2018, which covers 3,945,340 transaction records of 1,886,684 houses. I find that wildfires, especially distant wildfires, have a statistically significant detrimental impact on house prices via emitting PM2.5. There are also significant price disparities between houses located upwind and downwind locations of the wildfires, which may be explained by the substitution effect, externality, and the existence of other channels other than air pollution by which wildfires affect house prices. Moreover, the longer the property's adjacent areas remain free of wildfires, and the farther the nearest recent wildfire, the higher the property's sale price. While I find that households place a higher value on homes in locations with more greenery, they are also aware of the dangers of living near a wildland-urban interface.
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