Wildfires and Washington State Climatology

On the West Coast of the United States, wildfires have been an increasingly important issue ecologically, economically, environmentally, and socially. According to National Geographic, wildfires are defined as “uncontrolled blazes fueled by weather, wind, and dry underbrush, wildfires can burn acres of land—and consume everything in their paths—in mere minutes.” (Thiessen 2018). These fires occur mainly in the western portion of the United States partially due to decreased precipitation throughout parts of the year.

In Washington state, where this study will be focused on, they typically experience a ‘wet’ season that occurs variably between October and May depending on proximity to the Cascade Mountains (Cook et.

al 2017). The wet season for this region usually produces an average of 81% of the years precipitation. The remainder of the year there is very sparse precipitation, hence when most of the wildfires ignite. Based upon this year’s wildfires in Washington, the ‘wildfire season’ extended from June 2nd to October 15th. The length of the wildfire season can be characterized based on when the first fire ignites to when the final fire is contained (Union of Concerned Scientists 2013).

With more than 428,485 acres burned in just Washington state alone this year, there is an increasing concern for the intensity and frequency of wildfires throughout the state.

Not only are wildfires harmful to humans and wildlife, they pose a threat to infrastructure and local economies and are a costly disaster to combat. In 2015, the federal government spent excess of $1 billion just for wildfire suppression efforts (Thomas et.

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al 2017). On top of that, some states suppression expenditures usually fall around $1 to $2 billion a year (Thomas et. al 2017). With predicted increase in frequency and size, the price tag on wildfire mitigation will continue to grow. While you can put a price tag on putting out a fire, you cannot put a price tag on saving the ecosystems directly affected. Some of the other impacts from a wildfire on the environment include (Thomas et.al 2017):

• · Vegetation loss
• · Erosion of saturated areas
• · Flooding downstream from affected watersheds
• · Compositional changes in soil
• · Timber loss
• · Agriculture loss

This continual natural disaster is nothing short of dangerous and costly. Wildfires are also easily started and can spread rapidly. According to data from the Wildland Fire Management Information, wildfires are primarily started by humans. Between 2000 and 2017, 85% of fires were ignited due to human carelessness (U.S. National Park Service 2017). Most human caused fires are caused by unattended campfires, discarded cigarettes, and intentionally burning of debris or arson (U.S. National Park Service 2017). Another common cause to wildfires are those ignited by long-lasting cloud-to-ground lightning strikes (U.S. National Park Service 2017).

The identification of the potential causes to this variation in wildfire frequency and amplitude is crucial to be able to better predict and prepare for future wildfire seasons. Wildfires have been increasing in intensity and size progressively over time. This trend has been amplified since the 1980s and has consistently caused more damage to not only the environment but also the localized economies of those areas directly affected by fires (Westerling et.al 2006). According to previous studies, it has been found that precipitation deficits are the main cause of the variability of droughts in the Pacific Northwest (Cook et. al 2017). Another piece to this open-ended puzzle is the temperature variations interannually.

With the previous history of amplification of temperatures, the identification and understanding of its causes and effects will allow communities to better prepare for years to come. According to Westerling et.al, there were more wildfires in years that were warmer overall than in years that were cooler (2006). For the communities in the West and more specifically the Pacific Northwest, variations in temperature and precipitation are the main factors that drive drought which ultimately leaves the landscape more susceptible to wildfires (Crocket and Westerling 2018). These two factors have been chosen to be analyzed as it has been discovered that the “interannual variability in wildfire frequency is strongly associated with regional spring and summer temperature” as well as drought conditions (Westerling et.al 2006).

There have been many different theories as to what fuels the amplification of these fires. However, there are a few possible causes that will be compared to identify what the main contributor to these catastrophic events specifically in Washington state is. Within the state of Washington, topography plays a large part in precipitation patterns. Cities to the west of the Cascade Mountains often receive precipitation more consistently than cities to the east of the Cascades due to orographic uplift. For example, Seattle receives on average 37 inches of rain a year while Spokane receives 16.5 inches on average. Appropriately, only cities to the east of the Cascades were chosen for this study. The three cities being used in this study are Spokane, Wenatchee, and Kennewick. The three cities were selected based upon their larger populations and close proximity to wildfires occurring this year.

Spokane’s population is approximately 212,000 people who live in close proximity(which I defined as 25 miles) to 3 wildfire just this year. Wenatchee’s population is approximately 32,000 people who live in close proximity to 6 wildfires in 2018. Kennewick’s population is approximately 82,000 people who live in close proximity to an astonishing 10 wildfires this year. Each city is located in a different region of the state so a more representative sample of Washington would be utilized in this study. Prior to conducting any further research, the availability of current data as well as historical data was checked to ensure that data would be abundant to allow the comparison to occur. These cities all have differing climatological norms, so a wide range of conditions can better represent the entire state of Washington.

The most familiar way to analyze the spatial distribution of the cities and the wildfires that occurred this calendar year was to use GIS technology. The Northwest Interagency Coordination Center (NWCC) provides an ArcOnline Map that displays current fires, all fires to date in the current calendar year, archived fire data all the way back to 2000, current MODIS heat detection from the Terra and Aqua satellites along with other useful resources for tracking wildfires each season. This map is continuously updated as new information is available and is free to the public. You can also access the tabular data through this site how it was much simpler to correspond with the agency responsible for this map and obtain a copy of the shapefiles used for this online map. With the help of this online map, I was able to visualize the extent of wildfires within the state of Washington.

The remainder of the data for this study was collected via the National Weather Service’s Spokane Weather Office. All climatological data is based upon an average of all surface observations over the 30 year period between 1981-2010.

For each city in this study, two factors presented previously by other studies will be used to measure the ability of these two factors, temperature and precipitation variability to produce the conditions for a wildfire to start and spread. A measure of moisture commonly used by NOAA is the Palmer Severity Drought Index (PDSI) and will also be utilized as a measure of long term drought for this study. It is simply “a normalized drought index that integrates changes in supply and demand over multiple seasons” (Cook et.al 2017). Drought is driven by high temperatures and lack of precipitation, therefore, wildfires are more prone to ignite during drought conditions.

For Spokane, Washington the wet season (previously defined) of 2017-2018 was one of surplus moisture. Throughout this wet season, Spokane received an astonishing 3.91 inches more precipitation than climatology would have initially expected. With the abundance of moisture, it is safe for us to assume that this region experienced a surplus of fuel/vegetation growth, which could be an indicator for heightened wildfire ignitions. The PDSI for this time period leading up to the 2018 wildfire season remained within the mid-range(+/- 1.99) and moderately moist(+2.00 – 2.99), indicating that this region was receiving ample precipitation to account for the losses through evapotranspiration and still end up with a surplus. However, during the fire season the PDSI values meandered towards the other end of the scale. The values remained between the mid-range and moderate drought(-2.00 – 2.99).

These increasing drought values can be attributed to a lack of summertime moisture. Between June 2018 and the end of September 2018, Spokane only received 1.38 inches of precipitation as opposed to the climatological normal of 3.73 inches. That is a deficit of 2.34 inches. With this sort of deficit, we can accept the theory that having excess moisture to promote fuel source growth during the wet season leading up to the wildfire season along with a deficit in summertime precipitation can be a leading cause of heightened wildfire ignition.

While excess precipitation allowed the fuel source to grow, it must be dried out by warmer spring and summer temperatures. In Spokane, the temperatures were anything but warmer than usual. From March through September, only one month’s average temperature exceeded climatology, the remainder of the months fell anywhere from 1℉ to 4℉ below normal. For this region surrounding Spokane, it can be hypothesized that a surplus of moisture prior to the wildfire season and little precipitation during the wildfire season can be to blame for 2018 wildfires burning 557 acres in close proximity to Spokane however, high temperatures are not a significant factor in this specific situation.

For Wenatchee, Washington the values looked rather similar to those of Spokane. During their wet season, Wenatchee received more precipitation that normal between October 2017- May 2018, 0.85 inches more than usual to be exact. While a more modest amount of excess precipitation, it still contributed to the anomalously positive growth of fuel supply for these fires. The PDSI values show a similar story where they began as moderately moist( +2.00 – 2.99) and ended as mid-range. As for the PDSI values during the wildfire season, they began as mid-range and progressed into the moderate drought ( -2.00 – 2.99) throughout the region.

Between June and the end of September, Wenatchee only received a total of 0.139 inches of precipitation. That is a departure of 1.272 inches from normal. The lack of moisture from precipitation during the summer can be to blame for this drought and ultimately abundance of wildfire in this region that burned 9200 acres in close proximity to Wenatchee. Just like Spokane, temperature anomalies between March and September were analyzed to see if the theory that high spring and summer temperatures contribute to heightened wildfire ignition. During this period, temperatures were below average for more months than above average.

However, those months above average have larger anomalies such as a 6.5℉ departure from normal in May. These heightened temperatures may be causing this drying just before the wildfire season. With this result, the positive moisture anomaly will be the main identified cause to the wildfires affecting this region while temperatures play a more minor role.

Kennewick, Washington greatly varies from both Spokane and Wenatchee. Precipitation anomalies from October through May were actually negative as opposed to being positive throughout the later portion of the wet season. The region received 1.17 inches less than they are usually expected to.

During the fire season, Kennewick only received 0.12 inches when they would normally receive approximately 1.63 inches. While we can not attribute the increased wildfire ignition to additional fuel growth, the deficit of moisture may be the leading cause to fire spread. In 2018, a total of 14,817 acres within close proximity to the city of Kennewick were burned during this years wildfire season. While these drier conditions do not coincide with the current idea, they lead to another theory that “higher temperatures and dry conditions favor fire spread but these same conditions may also decrease plant growth..” (Kitzberger et.al 2017). The PDSI values for this region remained within the moderately moist( +2.00 – 2.99) to mid-range. The PDSI values during the wildfire season remained in the mid-range for the majority of the time but did reach moderate drought (-2.00 -2.99) towards the end of the season.

While excess fuel growth did not contribute majorly to the wildfire abundance in this region, temperature anomalies may be able to explain things a little better. For the spring and summer months leading up to the 2018 wildfire season, temperatures for Kennewick were significantly higher than the climatological norms. Temperatures ranged from 1.8℉ to 7.2℉ above normal. With a more consistent positive temperature anomaly combined with drier than normal conditions, this area is more susceptible to larger fires and easier ignition of fires. Length of season may also be increased with these type of conditions (Kitzberger 2017).

This study was relatively conclusive, however, further research can be conducted to solidify the theory that positive precipitation anomalies during the regions wet season and negative precipitation anomalies during the fire season are the main contributors to wildfire variability in Washington state. This same study can be conducted for the entire west coast or any region west of the rockies to identify if these same factors apply. A long term study looking at historical data provided by the NWCC can also better confirm the found theories. Other potential studies might include identifying the relationship between ENSO and PDO cycles and frequency of fires on a year to year basis as it has been found previous that these oscillations can alter the steering flow of weather systems that affect these regions (Cook et.al 2017). Finally, a study about growing season anomalies in years prior to the wildfire season and fuel availability and or a study on snowpack depths and timing of snow melt in the mountainous regions may be beneficial.

Following the analysis of temperature anomalies and precipitation prior to and during the wildfire season, it can be concluded in this region of Washington, that wildfires are mainly caused by the variability in precipitation. While positive temperature anomalies play a major role in Kennewick’s wildfire frequency, they were overall not as significant in altering frequencies for much of the state. With the knowledge gained from this study, communities in Washington and the Pacific Northwest may be able to better predict the amplitude of their fire seasons based upon analysis of their wet season precipitation anomalies. Officials and meteorologists can work in unison to better prepare the communities for the potential for higher frequency of wildfires.

With better forecasting of this phenomena, officials can better mitigate the potential for human caused ignition. The introduction of more strict burn laws or even prohibiting burning all together in tandem with larger fines can deter citizens from potentially starting a large disaster. Although there is nothing we can do to stop lightning ignition from occurring, communities can work together to avoid widespread burning of their homes.