Before beginning my research on the fire spread of the summer of 2009 in Los Angeles County, I used my previous knowledge of the local terrain to generate a hypothesis of how I believed the fire spread pattern would look. Knowing that the areas most prone to fire are located near steep topographic features and highly-flammable land cover, I thought that the fire pattern would remain somewhat contained on steeper topology with sparse vegetation. As the fire spread down the mountains and hills, I then believed the fire pattern would reach its maximum spread near the base of the steep features where the vegetation cover increased and the topology became flat, thus more prone to quickly spread the fire. I also believed that these flatter areas of topology would be located closely to urbanized, populated areas and therefore would pose an increased safety risk during the late summer months as the fires continue to increase in size and spread across larger areas.
In order to test my theories, I first began my research by downloading a map of LA County from the National Map Seamless Server (USGS, 2010). I chose to download the county map from this site because it highlights the topology of regions, thus would allow me to examine the terrain encompassed by the fire spread. After downloading this map, I then retrieved a shapefile of the Los Angeles County fire spread from August to September 2009 from the Los Angeles County Government’s GIS department site (Los Angeles County Enterprise GIS, 2009). Knowing that I not only wanted to map the fire spread in relation to the terrain/topology, but that I also wanted to map fire spread patterns in relation to their location in and around urbanized, populated areas in the county, I then went to UCLA’s MapShare site in order to download shapefiles based on 2000 Census data related to urbanized areas, populated areas, and census tracts in Los Angeles County (ESRI, 2008).
After downloading all of the shapefiles necessary to conduct my research, I then began to upload them into ArcView. I first uploaded the shapefile from the National Map Seamless Server in order to generate a hill shade map of Los Angeles County’s terrain. Creating the hill shade map would tell me which areas have the steepest terrain and which areas have the flattest. Next, I added all of the other census layers to the DEM in order to map the relations of urban/populated areas and the topology of the county. After placing all of the census overlays to the DEM, I then uploaded the fire-spread data over a four-day period. Finally when I completed inserting the overlay layers, I changed the color ramps and fills of each individual layer in order to make them all visible on the map.
After I completed the map, I then looked to analyze the pattern of the fire-spread upon the affected topology. Looking at the first day of fire spread (Fire Spread 1), I noticed that due to the light blue undertones of the magenta polygon, this fire was beginning to spread from the top of a steep topographic feature within the Angeles National Forest. I was also able to know that this was the top of a topographic feature because when looking at the center of the Fire Spread 1 polygon, I noticed that the topographic light blue lines converged into a distinct point, therefore indicating the top of a mountain or hill. This first day of fire-spread pattern reinforced my original hypothesis for according to the map the fire was concentrated in a small area on the steepest part of the terrain. When considering the spread of the fire over the terrain for the next three days, I also came to the conclusion that the data presented in my map reinforced other parts of my hypothesis for a number of reasons. First, when looking at the second day of fire, or Fire Spread 2, it is apparent that the fire was spreading down the mountain, as I originally had thought it would, and was still spreading in a pattern consistent with the first day, thus still continuing to spread in a contained manner toward the North. When looking at the third day of fire spread (Fire Spread 3), however, I noticed a change in the pattern of the fire. Again backing up my original theory, after analyzing the topology of the map I realized that this change was due to a change in the shape of the steep topographic features upon which the fire originally started. Looking at the map I realized around the third day, the fire spread had expanded towards the northeast and in no other direction as it had done in the previous days. This may have occurred because when considering the topology in the map, the topological features affected during day three of the fire spread are still located in steep areas (seen in the light blue undertones of Fire Spread 3), while those areas affected by the fire during day four have darker undertones indicating a flatter terrain. These differences in topology allowed me to conclude that before the fire could spread to the flatter areas in the northeast, it first needed to travel down the steep slopes of the terrain towards the northwest. Looking at the expansive spread pattern of Fire Spread 4, my hypothesis is once again reinforced. The darker undertones located under the orange-colored spread indicate that these areas are mostly flat terrain since the darker pink color on the DEM color-scheme indicates flat topology.
When analyzing the fire spread patterns in relation to locations of urbanized and populated areas, I was surprised to see how few census tracts the fires in summer of 2009 actually affected. Looking at the results on the map, my hypothesis was proven incorrect, for those urbanized/populated areas most affected by the fires were not only harmed during the late summer, but during the early and middle parts of the summer as well. All of the affected communities are located on the northern border of the populated and urbanized zones between the Valley and the Angeles National Forest in Los Angeles County. Considering the spread of the fire, it looked as if during the first day the fire may spread in a way that would support my hypothesis since it only harmed a small section of a one or two census tracts. As the spread expanded, however, it began to affect more and more communities each day, therefore refuting my suggestion that communities would only become affected on the last day of the spread once the fire reached flat terrain.
All of these areas affected by the fires qualified as both populated and urbanized regions. This characteristic allowed me to conclude that they have larger amounts of people per square mile than those areas that are classified as only populated and therefore can be considered high-risk communities “identified within the wildland urban interface (where structures and other human development meet or intermingle with undeveloped wildland)” (FRAP, 2010). In the state of California, these high-risk communities are required to develop Community Wildfire Protection Plans that “must be collaboratively developed (with agreement among local government, local fire departments and the state agency responsible for forest management), identify and prioritize areas for hazardous fuel reduction treatments, and recommend measures that homeowners and communities can take to reduce the ignitability of structures” (FRAP, 2010). During the 2009 Station Fire shown in the above map, one of the largest safety concerns for the affected communities was the risk of debris flows and flash floods occurring after the fire ceased. According to US News and World Report, the Station Fire of 2009 was one of the largest fires in the area’s watershed history and the park rangers and engineers were concerned that larger than normal quantities of debris would be captured by the flood control system and increase the systems stress and likelihood to burst under the pressure (US News and World Report, 2009, p.1). If the floodgates were to burst, the thousands of homes at the foot of the forest’s edge could be washed away and many larger animals that survived the fires could be forced to migrate into the communities on the flatter terrain. All of these events further increase the risk of living in the communities at the foot of the Angeles National Forest and reinforce the need for comprehensive wildfire/debris flow planning to take place in high-risk urbanized communities.
Works Cited:
Enhance Public Benefits from Trees and Forests: Planning for and Reducing Wildfire Risks. (2010). Fire and Resource Assessment Program (FRAP). Retrieved May 22, 2010, from California Department of Forestry and Fire Protection (FRAP) website: http://frap.fire.ca.gov/assessment2010/3.3_wildfire_planning.html
ESRI. (2008). Los Angeles County Census Tracts [Data file]. Retrieved from
http://gis.ats.ucla.edu//Mapshare/Default.cfm
ESRI. (2008). Los Angeles County Census Urbanized Areas [Data file]. Retrieved from
http://gis.ats.ucla.edu//Mapshare/Default.cfm
ESRI. (2008). Los Angeles County Populated Place Areas [Data file]. Retrieved from
http://gis.ats.ucla.edu//Mapshare/Default.cfm
Los Angeles County Enterprise GIS. (2009). All Station Fire Perimeters (as of September 2, 07:02) – Complete set [Data file]. Retrieved from http://gis.lacounty.gov/eGIS/?p=1055
Post-Wildfire Worries: Floods, Damaged Ecosystem. (2009, September 8). Retrieved May 22, 2010, from US News and World Report website: http://www.usnews.com/science/articles/2009/09/08/post-wildfire-worries-floods-damaged-ecosystem.html?PageNr=2
USGS. (2010). National Map Seamless Server [Data file]. Retrieved from http://seamless.usgs.gov/
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