Written by Emily Fischer, Sheryl Magzamen, Jeff Pierce, Monique Rocca, and John Volckens; Principal Investigators of Wildfires, Air Quality, Climate and Health a 2014-2015 SoGES Global Challenges Research Team.
Those of us living in the western US are familiar with wildfire smoke. Several months ago, a member of our SoGES Global Challenge Research Team (GCRT) was telling his mother that our team was researching the health effects of exposure to wildfire smoke. Her response was, “let me guess, it’s bad for you!” Of course, she is right (mom is always right), but it turns out this issue is complicated. There are are many open questions related to wildfire smoke, health and climate: Are the health effects of wildfire smoke different from automobile pollution or coal combustion? How well can we forecast where smoke plumes will go in order to warn those at risk of smoke exposure? How might wildfires change in the future? Can we manage our wildlands strategically to minimize wildfires and smoke exposure? In this post, we discuss why we need to answer these questions.
Are the health effects of wildfire smoke different from automobile pollution or coal combustion?
The World Health Organization has determined that air pollution is currently the world’s largest single environmental health risk, estimated to result in 7 million deaths annually. Specifically, fine particulate air pollution (particulate matter, PM) has been identified as contributing to lung disease, heart attacks and strokes. Wildfires are a very large source of summertime fine PM to the western US. On an annual basis, wildfire emissions account for about 10 - 40% of total fine PM emissions to the atmosphere. But are the health effects of wildfire smoke different from pollution from cars or power plants?
Wildfire smoke contains a complex mixture of gases (e.g. carbon monoxide and thousands of organic species) and PM. Particulate matter is a major concern because it tends to be more strongly correlated with health effects than other species. The peer-reviewed literature on public health impacts of wildfire smoke exposure (citations: ~80) is much smaller compared to research on general health effects of PM (citations: ~17,000) and human-generated (also called anthropogenic) PM such as diesel exhaust (citations: ~3,100). Consistent with health effects of human-generated pollution exposure, wildfire smoke exposure is associated with respiratory symptoms in vulnerable populations, such as children with asthma and patients with chronic respiratory and cardiovascular disease. Though studies on health effects of wildfire PM are methodologically comparable to those conducted on anthropogenic PM, several key findings indicate important key differences between the two types of exposure.
First, recent research on health effects of ambient PM has demonstrated that PM toxicity is a result of a complex interaction of particle size range, geography, source, and season. As health effects of human-generated PM (e.g. fossil-fuel combustion) have been studied primarily, it is unclear whether wildfire PM would have the same levels of toxicity. Second, it is unclear if anthropogenic PM and wildfire PM affect the same systems of the human body. Currently, PM-health research tends to focus on the cardiovascular effects of PM. However, several epidemiological studies have suggested that PM exposure from wildfire smoke is associated with respiratory, but not cardiovascular, morbidity. Animal models have demonstrated that wildfire PM is more toxic compared to equal doses of non-wildfire PM, and specifically target the lungs. In contrast, post-plume periods are associated with increased cardiovascular hospital admissions. Finally, a fundamental question in environmental epidemiology is understanding health effects of acute, high-doses of exposure (from a wildfire, for instance) compared to chronic, lower levels of exposure (from domestic wood burning).
How well can we forecast where smoke plumes will go in order to warn those at risk of exposure?
State and local agencies in charge of advising residents of poor air quality require accurate predictions of wildfire smoke concentrations (as far in advance as possible). Smoke forecasts are challenging for several reasons. (1) At best, smoke forecasts can only be as good as the underlying wind forecasts predicted by weather models. As weather predictions deteriorate forward in time, smoke forecasts will as well. (2) Fires in the western US often occur in mountainous regions where wind predictions are challenging due to channeling through valleys. (3) The spread and intensity of the fire must be predicted, especially for longer smoke forecasts. Spread and intensity forecasts require accurate information on the weather, the vegetation, and firefighting, and each includes uncertainties. (4) Smoke plume rise due to the heat of the fire must be accurately predicted. Hot fires may loft plumes away from the surface, and details of the atmosphere affect this rise as well. Thus, any uncertainties in the weather and fire spread/intensity will manifest itself as uncertainties in plume rise.
In light of these uncertainties, many agencies are developing and using smoke forecast tools. A popular tool among many decision-making agencies is the BlueSky smoke prediction tool developed by the US Forest Service. You can look at the current smoke forecasts from BlueSky for various regions of the US here. One of the goals of our SoGES GCRT is to evaluate and improve BlueSky and other wildfire prediction tools.
How might wildfires change in the future?
The area burned by wildfires in the western US has increased in recent decades, and modeling efforts consistently suggest that fire activity will continue to increase dramatically over the next century. However, these predictions have uncertainties. Many factors determine how wildfire occurrence has and will change, including the onset of snow melt, precipitation throughout the year, temperature, winds, humidity, vegetation, and human intervention (more details on this in the next question). All but this last factor depend on climate models for future predictions, and different models and different greenhouse-gas scenarios lead to different forecasts of these variables. Thus, the variability in future wildfire predictions is substantial. One of the objectives of our SoGES GCRT is to use a suite of climate models to determine what trends in wildfires seem to be robust across the various climate predictions.
Photo caption: From NRC 2011: Projected change in area burned for 1°C increase in global average temperature.
Can we manage our wildlands strategically to minimize wildfires and smoke exposure?
Beyond influencing climate change, there are two major ways in which humans can directly affect wildfires and smoke exposure . The first is involves how we develop our built environment along the urban-wildland interface. By building homes in and near forests at risk for wildfires, the folks who will live in these homes are not only at risk for wildfire smoke exposure, but may risk property loss!
The second way humans directly influence wildfires and smoke is through land management practices such as prescribed burning, forest thinning, and underbrush clearing. Such activities have the potential to reduce the spread rate, severity and, sometimes the occurrence of wildfires. As a consequence, these treatments may help to reduce smoke emissions and human health impacts during wildfires. On the other hand, the ecological appropriateness of such treatments varies greatly by ecosystem type. Further, while mechanical forest treatments have negligible air quality impacts, prescribed fire substitutes limited and somewhat controllable air quality impacts over many burn periods for potentially severe and unplanned air quality events. The health tradeoffs of wildfires versus prescribed fires have not been extensively evaluated. Our GCRT is investigating how these various wildfire-mitigation approaches may impact wildfires and air quality.
Photo caption from first image: Wildfire smoke from the High Park Fire (June, 2012) obscuring the sun over Fort Collins, CO.