By Priscilla Hare, MESM '20
Fires destroy hundreds of thousands of acres each year in California alone, costing hundreds of millions of dollars, and many reports predicting increased fire severity with climate change. Just this past year, California was hit with its two largest wildfires in history: the Thomas fire began in December 2017 and burned 280,000 acres, and the Mendocino Complex Fire began in July 2018, burning nearly 460,000 acres.[i] Combined, this is over the size of Rhode Island. This past year the state was also hit with its deadliest fire: the Camp Fire that started in November 2018 burned over 150,000 acres and killed over 80 people. Extreme fires like these damage buildings and homes, take lives, and severely affect the landscape. Is this the future for the western United States?
A recent study of wild land fire severity in the western United States may have the answer. The study reported that human activities, such as fire suppression, are the cause of this increased severity.[ii] Fire suppression creates an environment with an excess of vegetation.[iii] A warmer climate leads to the drying out of this vegetation, leading to increased fuel. In this way, fire suppression has created a tinderbox.
Increased fire severity affects vegetation makeup, wildlife habitat, carbon emissions, erosion rates, infrastructure, and human safety.[iv] Fires impact what plants grow back post burn and lead to hundreds of thousands of acres of wildlife habitat being destroyed. Burning trees releases carbon into the atmosphere, exacerbating climate change. Vegetation loss results in increased erosion rates, as can be seen with the mudslides that occurred after the Thomas Fire. Fire severity also impacts the number of structures burned and human safety, with potential respiratory impacts and death.[v] The Mendocino Complex Fire burned nearly 300 structures, the Thomas Fire burned over 1,000, and the Camp Fire over 18,000.[vi]
The first step in the process of preventing increased fire severity is combatting the history of fire suppression that leads to altered fire regimes and vegetation dynamics.[vii] Counteracting the long history of fire suppression involves prescribed fires and mechanical thinning of forests. If forests can be successfully managed to have less vegetation, models suggest that fire severity will lessen.[viii]
Statistical models have been created to predict how fire severity changes with lower vegetation levels expected to come with climate change. Parks et al. used fire intensity data from 1984 to 2012 to create models of fire severity as a function of climate. Climate for this time period was represented using temperature along with variables linked to fire regimes: evapotranspiration, water deficit, annual precipitation, soil moisture, and snow water equivalent.[ix] The model was then used to predict fire severity between 2040 and 2069 based on climate change projections. The model determined that climate change should weaken fire severity. A warmer and drier climate is predicted to increase vegetation loss, creating less fuel for fires to burn.[x] So how could two major fires burn through so much land if fire severity is supposedly weakening?
The model used to make this prediction is not useful for present conditions caused by altered vegetation levels from fire suppression. Dried vegetation needs to be removed for these models to be used to predict fire severity levels. However, there are many acres of forests that need costly active management, calling for a method of selecting optimized management areas.
New studies show that optimized management areas can reduce fire severity by nearly 20%, compared to no management.[xi] This study looked at models for applying treatment in optimized areas with highest modeled severity, as opposed to randomized areas, or no management at all. Optimizing the targeted management zones leads to greater success at reducing fire severity and creating more stable and resilient forests.
Management of forests can lead to the reduction of fire severity in an agreement with climate models. The future of the western United States does not have to be written by extreme fires.
References
[i] “Top 20 Deadliest California Wildfires.” CalFire, CA.gov, 12 Dec. 2018.
[ii] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[iii] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[iv] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[v] Rappold, A.G., et al. “Community Vulnerability to Health Impacts of Wildland Fire Smoke Exposure.” Environmental Science & Technology, vol. 51, 2017, pp. 6674-6682.
[vi] Top 20 Deadliest California Wildfires.” CalFire, CA.gov, 12 Dec. 2018.
[vii] Krofcheck, Daniel J., et al. “Prioritizing forest fuels treatments based on the probability of high-severity fire restores adaptive capacity in Sierran forests.” Global Change Biology, vol. 24, 2018, pp. 729-737. Doi:10111/gcb.13913.
[viii] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[ix] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[x] Parks, Sean A., et al. “How will climate change affect wildland fire severity in the western US?” Environmental Research Letters, vol. 11, 2016.
[xi] Krofcheck, Daniel J., et al. “Prioritizing forest fuels treatments based on the probability of high-severity fire restores adaptive capacity in Sierran forests.” Global Change Biology, vol. 24, 2018, pp. 729-737. Doi:10111/gcb.13913.