roduces longer, drier fire seasons and extensive burning; and b) patterns of human development are increasing human exposure to wildfires (Abotzoglou and Williams 2016; Radeloff et al. 2018).
In Montana, increased fire activity in recent decades has impacted people through an increase in hazardous air quality from wildfire smoke, originating locally or from distant sources (see, for example, Figure 3-6). For the western US, including Montana, warmer and drier conditions during summer have contributed to longer fire seasons and more area burned by wildfires, producing more and longer smoke events (Dennison et al. 2014; Westerling 2016; Dalton et al. 2017). Smoke events in the western US from 2004–2009 were associated with a 7.2% increase in respiratory hospital admissions among adults over 65 yr of age (Liu et al. 2017).
Human response data connecting heat and smoke to human health are limited for Montana. In nearby Boise, Idaho, however, seven of the last ten years have included smoke levels considered “unhealthy for sensitive groups” for at least a week during the fire season (IDDEQ 2013), causing cancellation of some school-related sports activities (Nolte et al. 2018). In 2020, large fast-moving fires in California, Colorado, Oregon, and Wyoming resulted in days with the air quality index rated “hazardous” in locations across the western US.
Air quality hazards from wildfire
Wildfire smoke worsens local air quality (Navarro et al. 2016), with substantial public health impacts in regions with large populations near heavily forested areas (Liu et al. 2015; Reid et al. 2016a; Fann et al. 2018). Smoke decreases visibility causing hazardous conditions (Yue et al. 2013), and can be transported hundreds of miles downwind (Dreessen et al. 2016; Kollanus et al. 2016).
Wildfire smoke contains many components that are hazardous to human health, including particulate matter (more below), polyaromatic hydrocarbons, carbon monoxide, nitrous oxide, aldehydes, benzene, among other components (Reisen et al. 2015; Adetona et al. 2016; Liu et al. 2016).
Exposure to wildfire smoke can result in emergency room visits for a variety of conditions, newly caused or aggravated, including asthma and chronic obstructive pulmonary disease (Rappold et al. 2011; Tinling et al. 2016; Cascio 2018); and cardiovascular conditions, including stroke, heart attack, and heart failure (Dennekamp et al. 2015; Haikerwal et al. 2015; Hutchinson et al. 2018; Wettstein et al. 2018). Additionally, wildfires can lead to rapid ozone formation and increased frequency of ozone pollution levels that exceed air quality standards (Jaffe et al. 2008; Jaffe and Widger 2012). Increased ozone pollution harms human health, as described previously.
Wildfires are estimated to have contributed about 18% of the total atmospheric particulate matter emissions in the US from 2004-2009 (Liu et al. 2015). Wildfires are projected to become the principal driver of summer particulate-matter concentrations in the western US (Ebi et al. 2018).
A study by Liu et al. (2016) shows that on days in the US exceeding regulatory particulate matter (PM2.5) standards, wildfires contributed an average of 71% of total particulate matter (PM2.5). Under future climate change, they estimate that more than 82 million individuals will experience a 57% increase in frequency and a 31% increase in intensity of smoke waves, defined as two or more consecutive days with high, wildfire-associated increases in particulate matter. They additionally project that wildfire-associated particulate matter will increase 160% by mid century under the RCP4.5 scenario (see Section 2).
Airborne particulate matter is expected to increase in Montana croplands with more soil-exposed fallow periods (Pi and Sharratt 2017). Wind erosion of soil in wheat production is likely to increase due to increased summer drought and changing precipitation patterns favoring winter wheat over spring wheat. Climate change is also likely to create more cropland abandonment leading to desertification and land degradation (Hughes and Diaz 2008).
Ex