A Coast Ablaze Part I: Environmental Causes of California Wildfires

Written by: Justin Perry '23
​Edited by: Nina Mehta '22

Ryan J, Mack E. Latest on wildfires in California, Oregon and West. Plus, how to help - CNET [Internet]. Cnet. 2020 [cited 2020 Oct 20]. Available from: https://www.cnet.com/how-to/updates-on-wildfires-ravaging-california-oregon-and-west-and-how-to-help/

Since this past August, the state of California—indeed the entire West Coast—has experienced devastating wildfires. The Bobcat Fire, for instance, has killed more than 25 people and burned nearly 115,800 acres and over 100 homes. By September 13, wildfires had scorched an area of forest and brush land equivalent to the size of New Jersey. On September 9, the August Complex fire in the Coast Range of Northern California became the largest fire in California history. While summer and fall wildfires have been frequent, natural occurrences, the size and scope of recent fires has been astonishing. Even though the seasonal Santa Ana winds, which usually trigger an increase in wildfires, had not yet arrived, California wildfires burned about 3.2 million acres from January to mid-September 2020, nearly half of the total land area burned from 2001-2010. In the past decade, California wildfires have destroyed nearly 30,000 structures, (1) roughly five times the number of structures in downtown Los Angeles.

Considering the unprecedented nature of this destruction, it is logical to hypothesize that environmental and human factors have altered the delicate balance of West Coast forest and brush lands. Since 1990 the average summer temperature in California has increased from 71.3°F to 75.4°F. While this trend may not be concerning at first glance, periods of extreme heat in late August and early September—peak wildfire season—have led to record-breaking high temperatures. During one such heat wave, a 121°F high was recorded Los Angeles on September 6, 2020. (1) Unfortunately, it appears that such heat waves will continue to increase in frequency, duration, and intensity due to climate change according to a recent study that analyzed heat wave trends across Southern California from 1950-2020.

This warming trend has led to heightened wildfire risk, as it has “increased the likelihood and magnitude of drought … and increased vegetation stress and forest mortality.” (2) However, drought is not solely the result of rising temperatures on land. The 2011-2019 drought became particularly severe due to a unique combination of new oceanic and atmospheric trends. During several winters beginning in 2013, an anticyclone (a circulating weather system with high atmospheric pressure at its center) (3) began to extend from the central Pacific Ocean to northern Oregon. (4) The recurring anticyclone, dubbed the Ridiculously Resilient Ridge (RRR) by Stanford graduate student researcher Michael Swain, repeatedly diverted winter storms to Baja California, Oregon, and Washington. The diversion of winter storms was further compounded by the emergence of the “Blob,” a region of abnormally high ocean surface temperatures produced by the RRR (5) that decreased the amount of snowfall in the few storms that did reach the West Coast. (6) Considering that these storms would normally travel via the jet stream from the central Pacific to the western United States, the accumulation of rain and mountain snowpack substantially decreased. Although the drought is technically over as of March 2019, (7) the fact that it lasted for such a long period of time (before the El Niño of winter 2016-2017 disrupted the RRR) has amplified its effect such that it was likely the most severe drought in over 1200 years.

As can be expected, the California drought, compounded by warming temperatures, has led to a significant accumulation in the amount of dead forest matter. Surprisingly, there has been much greater tree mortality than predicted when considering warming temperatures and drought conditions. Drought-induced changes in tree physiology have weakened trees’ natural defenses and led them to be vulnerable to bark beetle infestation. The severity of the combined effect of drought and beetle infestation was supported by a study of ponderosa pines in which the pines that were deprived of water in the presence of bark beetles had the highest mortality. As a result, extreme drought stress and bark beetle proliferation have caused more than 129 million trees to die between 2012 and 2016. (8)

It is worth noting that environmental processes such as rising temperatures and severe drought do not happen in isolation, as they seem to be influenced by human factors. There is evidence to suggest that anthropogenic, or human-caused, climate change is responsible for affecting atmospheric circulation patterns (like the RRR), increasing the occurrence of warm and dry weather. (9) In addition, climate modeling experiments that take into consideration the presence and absence of human factors substantiate that “human activities have increased the probability that dry precipitation years are also warm.” (10) While human activity has not only contributed to these macro-scale environmental processes, it has also had a direct impact on forest ecology, as anthropogenic increases in forest fuel aridity (which increases susceptibility to fires) have exceeded the expectations for natural increases in forest fuel aridity from 1984-2015. (11) As a result, an estimated 4.2 million hectares of burned forest can be attributed to anthropogenic climate change.
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Given the severity of the California wildfires and the magnitude of their causes, this problem might seem too monumental to solve. However, there are some intermediate steps that could be taken that would at least be a “step in the right direction.” For instance, there is near universal agreement in the scientific community that proper forest management reduces the risk and severity of wildfires. Even so, some debate remains as to what constitutes proper forest management. Most environmental scientists agree that since forest health has historically been preserved by frequent mid- to low-intensity fires, the most logical approach would include controlled burns. Controlled burns seem logical, as a lack of major fires has led to more crowded forests, increased competition for limited resources like water, and the presence of more fire-intolerant plant species. (12) These conditions can be extremely detrimental for forests, as they provide more fuel and allow wildfires to spread more rapidly. However, there is a lack of confidence in the safety of controlled burns within rural areas that would be directly impacted, (13) and there have been concerns about frequent smoke exposure and negative effects on the lumber industry. Forest thinning, an alternative—and perhaps a complement—to controlled burning, would perhaps be more useful in vulnerable rural areas. Unfortunately, forest thinning is also quite costly and labor intensive. Considering that the United States Forest Service spent more than $2.6 billion to suppress forest fires in 2018 and that spending on fire suppression has grown to include half of the agency’s budget, it appears as if there is simply a shortage of money to spend on fire prevention measures. (1)

​Works Cited:

1.   Krishnakumar P, Kannan S. 2020 California fires are the worst ever. Again. [Internet]. Los Angeles Times. [cited 2020 Oct 11]. Available from: https://www.latimes.com/projects/california-fires-damage-climate-change-analysis/
​2.     Goss M, Swain DL, Abatzoglou JT, Sarhadi A, Kolden CA, Williams AP, et al. Climate change is increasing the likelihood of extreme autumn wildfire conditions across California. Environ Res Lett. 2020 Sep;15(9):094016.
3.     Anticyclone | Definition of Anticyclone by Merriam-Webster [Internet]. [cited 2020 Nov 8]. Available from: https://www.merriam-webster.com/dictionary/anticyclone
4.     Than K. Causes of California drought linked to climate change, Stanford scientists say [Internet]. Stanford University. 2014 [cited 2020 Oct 15]. Available from: http://news.stanford.edu/news/2014/september/drought-climate-change-092914.html
5.     Bond NA, Cronin MF, Freeland H, Mantua N. Causes and impacts of the 2014 warm anomaly in the NE Pacific. Geophys Res Lett. 2015;42(9):3414–20.
6.     Rice D. How “the blob” caused USA’s weird weather [Internet]. USA TODAY. [cited 2020 Oct 15]. Available from: https://www.usatoday.com/story/weather/2015/04/20/blob-weird-weather/26073153/
7.     California | Drought.gov [Internet]. [cited 2020 Oct 14]. Available from: https://www.drought.gov/drought/states/california
8.     Restaino C, Young DJN, Estes B, Gross S, Wuenschel A, Meyer M, et al. Forest structure and climate mediate drought-induced tree mortality in forests of the Sierra Nevada, USA. Ecol Appl Publ Ecol Soc Am. 2019;29(4):e01902.
9.     Mann ME, Gleick PH. Climate change and California drought in the 21st century. Proc Natl Acad Sci U S A. 2015 Mar 31;112(13):3858–9.
10.     Diffenbaugh NS, Swain DL, Touma D. Anthropogenic warming has increased drought risk in California. Proc Natl Acad Sci. 2015 Mar 31;112(13):3931–6.
11.     Abatzoglou JT, Williams AP. Impact of anthropogenic climate change on wildfire across western US forests. Proc Natl Acad Sci U S A. 2016 Oct 18;113(42):11770–5.
12.     Voelker SL, Merschel AG, Meinzer FC, Ulrich DEM, Spies TA, Still CJ. Fire deficits have increased drought sensitivity in dry conifer forests: Fire frequency and tree-ring carbon isotope evidence from Central Oregon. Glob Change Biol. 2019;25(4):1247–62.
13.     McCaffrey SM. Prescribed fire: What influences public approval? :7.



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