The Era of Extreme Wildfire

11 March 2019

KIMBERLY ROBERTS – Vice President and Meteorologist JLT Re, Denver, CO

The general expectation heading into summer 2017 was that the wildfire season might be less active than typical due to very heavy winter snows and spring rains in the Western U.S. Contrary to this belief, the season was on-par with the worst in recent history, as fires burned over 9 million acres across the U.S. While the winter of 2018 saw average levels of precipitation, another exceptionally hot and dry summer in California led to a record breaking wildfire season, equaling if not eclipsing, the damaging 2017 season. While the severity of the recent California fires has drawn attention to this peril, the two consecutive seasons are actually not complete outliers in the context of the past decade. Devastating fires occurred along the Front Range in Colorado in 2012 and 2013, followed by the worst fire season on record for the state of Washington in 2015, impacts, burned acreage, structure loss and massive structure losses in Fort McMurray loss of life. This escalating focus on wildfire and Gatlinburg in 2016, and now the past has led to a question that is on many minds: two seasons that were most notable in terms is the recent elevated frequency and severity of suppression costs, evacuations, smoke of fires an anomaly or the new normal? 

Figure 1: Wildfire Acreage Burned Annually in the United States. (Source: National Interagency Fire Center (NIFC))

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A DISASTROUS COMBINATION: WIND, FUEL AND URBANIZATION

Wildfire in the fall is quite common in California, as the ground is driest and the winds are strongest. Winds generated by strong high pressure systems over the Great Basin drive air down from the mountains toward the coast, warming in the process. These hot, strong winds are known as the Santa Ana winds in Southern California and the Diablo winds in Northern California. Sustained wind speeds can reach up to 60 miles per hour, with gusts much higher, and mainly occur in the fall and winter months (Figure 2). 

Wildfire catastropheFigure 2: Schematic of Santa Ana and Diablo winds set-up in the fall and winter months in California. (Source: JLT Re)

Strong winds alone are not sufficient to cause the extreme wildfires that have occurred the past few seasons. A second key component is an ample fuel source, which was in abundance both years. The 2017 season was characterized by an extremely wet winter and spring, while 2018 winter precipitation was at a normal level. This moisture was a welcome relief to long-term drought conditions and kept wildfire risk at a minimum through the early spring, however it also served as a source for heavy vegetation growth. New brush growth can be very flammable and create embers that have the ability to travel a considerable distance. What this all means is that despite common perception, winter rain is not an accurate predictor of wildfire activity; the wildfire season is ultimately driven by temperature and precipitation during the summer and fall. The 2017 Tubbs, Nuns, Atlas and Thomas Fires occurred on a backdrop of exceptionally hot and dry summer conditions, eclipsed only by the record-breaking heat of the summer of 2018, which provided fuel sources for the destructive Carr, Mendocino, Camp and Woolsey Fires (Figure 3). 

Figure 3: Average California summer temperature and precipitation conditions for wildfire seasons 1895 – 1919. (Source: Twitter @RARhode)Wildfire catastrophe

The exceptional nature of these recent fires is not only in the fact that they simply occurred, but their location – namely some of the largest metropolitan regions in North America. This highlights the third key component of damaging wildfire; the ever growing issue of population spreading into the wildland urban interface (WUI). Over time, the edges of sprawling urban areas in the U.S. and Canada have begun to encroach on wild spaces where vegetation conditions are favorable for fueling wildfire. There has been a 720% population increase since 1960 in WUI areas in the U.S., a jump from 25 to 140 million people. This migration into the WUI is occurring within a setting of more fires, more homes destroyed, more acreage burned and escalating fire-fighting costs. The probability of a fire ignition due to humans or infrastructure becomes more likely as people enter this vulnerable space. The combination of burnable vegetation and wood frame or combustible material homes can lead to a rapid spread of fire and thus greater loss. All of the most heavily damaged communities in the past two seasons of California fires were in the interface between urban and forest areas.

Figure 4: WUI region in the North Bay Area of California, with the October 2017 wildfire perimeters overlaid. (Source: Silvas Lab and JLT Re)

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Figure 5: Wildfire destruction in the Coffey Park neighborhood of Santa Rosa. (Source: Marcio Jose Sanchez via @ 2018 The Associated Press)

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The Wildfires of 2017 and 2018

The weather and fuel components were all in place for a large and dangerous fire going into October 2017 in California. On the night of October 8th, winds in excess of 50 miles per hour were observed in the valleys of Northern California, with gusts of 70 plus miles per hour along the higher ridgelines. Combined with ample fuel and low relative humidity, the fires spread rapidly, often jumping from ridgeline to ridgeline as embers traveled considerable distances on the strong winds. The result was a fire storm of devastating proportion, which rapidly overwhelmed entire neighborhoods in Santa Rosa, Napa and Sonoma over several days. Over 14,000 structures were damaged or destroyed either directly by the fire or indirectly by smoke damage. Insured losses are estimated at over US$8.5 billion and growing, making it the costliest wildfire to date in U.S. history.

Figure 6: Ember-driven fire spread during the Camp Fire. (Source: Noah Berger via © 2018 the Associated Press)

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Unfortunately the fire season was not over after the Northern California outbreak; in early December 2017, the Thomas Fire in Southern California began to burn the hillsides around Ventura and Santa Barbara, driven by the Santa Ana winds. Over 1,200 properties were destroyed with many thousands more threatened as the wildfire progressed with only minimal containment for weeks. All of the major conditions for extreme, loss-causing fire were in place in December: dry fuels, dense population adjacent to wilderness ignitions and recurring Santa Ana wind conditions. While the October Tubbs fire was the most destructive wildfire event in California at the time, the Thomas Fire became the most extensive in terms of acreage burned.

Figure 7: 2017 and 2018 initial California Wildfire Perimeters. (Source: GeoMac and JLT Re)Wildfire catastrophe

July of 2018 saw a reemergence of favorable wildfire conditions in California, as temperatures exceeded any July on record. The Carr fire ignited near Redding, CA due to flying sparks from a blown out tire, and was characterized by extreme fire behavior, including an immensely destructive fire tornado. The winds within this fire-generated vortex were in excess of 140 miles per hour, as evidenced by tornado-type damage within the fire footprint. The Carr fire landed in the top 10 most destructive and largest wildfires in California history. Burning concurrently, the Mendocino Complex Fire became the single largest fire in the state, although property damage was not as extensive as it burned in a less populated area.

After a short quiet spell, the Santa Ana winds kicked back up in the fall and the most destructive wildfire in U.S. history was ignited on morning of November 8th 2018, and completely destroyed the town of Paradise, CA. Once again it proved to be a combination of extreme winds, ample fuels and a vulnerable population that triggered such a destructive and deadly fire. It moved rapidly through the town of Paradise in a single day, demolishing 14,000 structures and killing 85 people. At the same time in Southern California, the Woolsey Fire was destroying properties in Malibu, Agoura and Thousand Oaks. With a 2018 wildfire season that is arguably even worse than the damaging 2017 season, many questions have risen regarding how to manage the ever-increasing wildfire threats and how to leverage lessons learned to create actionable insights.

Lessons Learned

Certain shared characteristics of the wildfires of 2017 and 2018 can help change the way wildfire risk is managed in vulnerable communities. While each fire had its own distinct cause and contributing factors, there were similarities that can be identified and explored. The confluence of wind, fuels and people cannot be avoided, however it can be mitigated.

Communities are continuing to develop mitigation strategies that stretch beyond the efforts of an individual home or business owner. Safety measures taken at the structural level can be very useful, however creating neighborhood buffer zones and ensuring ample points of access in communities are also extremely important. The extreme nature of recent wildfires, fueled by increasingly hotter summer temperatures, means that often in the critical first stages of spread, fire­fighting resources are focused exclusively on evacuation and human safety, which means the fire can spread unabated. This highlights the necessity for community-level zoning, building evacuation, response and communication plans that go beyond the level they are at today.

Figure 8: Destruction from the Thomas Fire in Ventura, CA, highlighting the need for defensible space. (Source: JLT Re)Wildfire catastrophe

Increasingly, however, fire intensity and spread rates are simply too great to suppress, even if fire-fighting resources are available. The Camp Fire was characterized as a wildland fire, however it can be argued that it translated into an urban conflagration once it entered the town of Paradise. The ember-driven fire jumped from structure to structure, accelerated by extreme Santa Ana winds, often leaving tree leaves and vegetation intact. This type of behavior was observed by the JLT Re team after the Tubbs Fire in Santa Rosa, particularly in the communities of Coffee Park and Fountaingrove. Wide concrete streets, irrigated fields, orchards and golf courses were once considered adequate defensible spaces, areas around a structure that are maintained and designed to reduce fire danger. However given the drought-created fuel situation and increasingly ember-driven fires, these buffers are no longer providing sufficient protection. Communities that were once considered low risk and suburban/urban are now burning at alarming rates. Populations adjacent to wildland must consider planning for urban conflagration in addition to more traditional interface wildfires.

Finally, recent events have shown us that the impacts from wildfire continue well after the flames are extinguished. Vegetation typically holds soils in place during excessive rainfall events. In a vegetation-free burn scar environment, the burned soil can become quite water-repellent and unable to absorb water as it normally would. These post-burn conditions significantly increase the potential for mudslide, becoming an additional cause of damage and loss from both the costs of evacuation to structure damage. Notable examples are the communities of Montecito after the Thomas Fire and Malibu after the Woolsey Fire. Typically homeowners insurance does not cover the mudslide peril, which is more commonly covered through a flood or earth movement insurance policy, neither of which are often purchased. However, homeowners policies do cover fire-related damages, and in this case could potentially include mudslides caused by burn scar. There will likely be meaningful changes to what policies cover given the increasing correlation between late season wildfire and winter precipitation events that lead to mudslides.

Climate Change and Wildfire

As population continues to grow into wildfire-prone regions, there is an increasing interest in the scientific community to determine the fingerprint of climate change on extreme weather and how this might relate to wildfire frequency and severity in the future. JLT Re meteorologists attended a recent conference at Columbia University on Wildfire Prediction, where scientists discussed how climate change is affecting wildfire activity in several key ways. Certain aspects are better understood than others; we know that a warmer climate will lead vegetation to dry out, which will provide greater fuel sources for wildfire. There is also evidence suggesting that lightning will occur in greater frequency in warmer climates – as much as 12% more strikes per degree Celsius rise in temperature, further influencing fire ignition. Moreover, studies show that spring may be arriving earlier going forward – by as much as three weeks. This not only lengthens the warm fire season, but it also impacts the timing of snowmelt and the ability for soil and vegetation to remain moist into fire season.

Figure 9: Homes destroyed by the Tubbs Fire located between an irrigated golf course and a four-lane road in the Fountaingrove community in Santa Rosa. (Source: JLT Re)

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Figure 10: A Cal Fire search and rescue crew looks over a home damaged by storms in Montecito, Calif., Friday, Jan. 12, 2018. The mudslide, touched off by heavy rain, took many homeowners by surprise early Tuesday, despite warnings issued days in advance that mudslides were possible because recent wildfires had stripped hillsides of vegetation that normally holds soil in place. (Source: © 2018 The Associated Press/Marcio Jose Sanchez)

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Future Changes In Fire Probability From 16 Climate Models
Climate modeling studies are emerging which aim to quantify frequency and severity of fire into the mid-century, based on various greenhouse gas emission scenarios. This is a complex task given the interconnectedness of the ocean and atmosphere systems, as well as background climate variability that can alter rainfall and temperature patterns on varying timescales. Despite some uncertainty, most of these studies point to increasing wildfire risk, with the study shown in Figure 11 indicating that by the end of the 21st century, there will be a 25% increase in susceptibility to wildfire in the Western U.S. and Boreal Canada.

Figure 11: Predicted fractional change in fire probability for the period 2010 – 2039 (top) and 2070 – 2099 (bottom) for the average of sixteen climate models used for the 2007 IPCC report. For the 2070 – 2099 period, the models agree that 20% of Earth will see decreases in fire probability, 62% will see increases, and the models are too uncertain to tell for the other 18%. (Source: Climate change and disruptions to global fire activity, Moritz et al., 2012, Ecosphere)

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With evidence of long and large wildfire seasons occurring with greater frequency, it remains vitally important that the insurance industry encourage effective mitigation techniques and develop strategies to cope with growing accumulations of risk that are vulnerable to wildfire, particularly in light of both urbanization and climate change.

Here at JLT Re, we are continually improving our wildfire expertise, while innovating and incorporating analytics to provide insight into this increasingly significant peril.