4.6 Wildfires

Climate change is projected to increase the frequency and intensity of large wildfires (Figure 4.4), with associated health risks projected to increase in many regions.1,2 Wildfire can have health impacts well beyond the perimeter of the fire. Populations near the fire or even thousands of miles downwind may be exposed to a complex smoke mixture containing various substances including carbon monoxide, ozone, toxic chemicals, and both fine and coarse particles,3,4 presenting a serious health risk for the exposed populations (see Ch. 3: Air Quality Impacts).5,6 For example, the 2002 forest fires in Quebec resulted in up to a 30-fold increase in airborne fine particulate concentrations in Baltimore, Maryland, a city nearly 1,000 miles downwind.1 Exposure times can range from a few days to several weeks.3,7,8


Figure 4.4: Projected Increases in Very Large Fires

Figure 4.4:  Projected Increases in Very Large Fires
Based on 17 climate model simulations for the continental United States using a higher emissions pathway (RCP8.5), the map shows projected percentage increases in weeks with risk of very large fires by mid-century (2041-2070) compared to the recent past (1971-2000). The darkest shades of red indicated that up to a 6-fold increase in risk is projected for parts of the West. This area includes the Great Basin, Northern Rockies, and parts of Northern California. Gray represents areas within the continental United States where there is either no data or insufficient historical observations on very large fires to build robust models. The potential for very large fire events is also expected to increase along the southern coastline and in areas around the Great Lakes. (Figure source: adapted from Barbero et al. 2015 by NOAA)50

Exposure to smoke-related air pollutants from wildfires has been associated with a wide range of human health effects, including early deaths and low infant birth weight, with the strongest evidence for acute respiratory illness.3,4,9,10,11,12,13 Inhalation of smoke from wildfire has been linked to exacerbated respiratory problems, such as shortness of breath, asthma, and chronic obstructive pulmonary disease (COPD).12,14,15,16 While the association between smoke exposure and cardiovascular outcomes is uncertain,12 exposure to fine particles contributes to risk of cardiovascular disease and premature death.17,18,19,20

Firefighters battling fire

Exposure to smoke-related air pollutants from wildfires has been associated with a wide range of human health effects.

Wildfires can also affect indoor air quality for those living near affected areas by increasing particulate matter concentrations within homes, leading to many of the adverse health impacts already discussed.7,21 For example, during the 2007 San Diego wildfires, health monitoring showed excess emergency room visits for asthma, respiratory problems, chest pain, and COPD. During times of peak fire particulate matter concentrations, the odds of a person seeking emergency care increased by 50% when compared to non-fire conditions.22 Smoke from wildfires can also impair driving visibility, increasing risks of motor vehicle deaths and injuries.23,24,25,26

Pregnant women, children, and the elderly are more sensitive to the harmful health effects of wildfire smoke exposure (see also Ch. 9: Populations of Concern).27,14,28,29 Firefighters are exposed to significantly higher levels and longer periods of exposure to combustion products from fires, leading to health risks that include decreased lung function, inflammation, and respiratory system problems, as well as injuries from burns and falling trees.3,28,30,31,32,33

Wildfires can also create an increased burden on the health care system and public health infrastructure. For example, wildfires near populated areas often necessitate large evacuations, requiring extensive public health resources, including shelter, and treatment of individuals for injuries, smoke inhalation, and mental health impacts.34,25,35,36 Housing development in or near the wildland–urban interface has expanded over the last several decades and is expected to continue to expand.37 These changing development patterns in combination with a changing climate are increasing the vulnerability of these areas to wildfires.38,39,40

Following wildfire, increased soil erosion rates and changes to runoff generation may contaminate water-supply reservoirs and disrupt downstream drinking water supplies.41,42 Post-wildfire erosion and runoff has been linked to increased flooding and debris flow hazards, depending on the severity of the fire, seasonal rainfall patterns, watershed characteristics, and the size of the burn area.43,44,45,46 Wildfires have a range of short- and long-term effects on watersheds that have the potential to change water quality, quantity, availability, and treatability downstream from the burned area.47,48,49


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