Fire Station Map of Angeles National Forest (above 210-Freeway)
The Santa Ana Winds
The wildfires of Southern California are often associated with the vegetation that dominate the landscape. Dense chaparral and invasive grasses ignite quickly and spread rapidly to create devastating fires that scorch the hills of Los Angeles County and its surrounding population. However, larger forces are at work, namely, the Santa Ana Winds. Predominant in late summer and early fall, the Santa Ana Winds create gusts that blow up from the mountains in the East towards the coast. The combination of dry, flammable vegetation and high populations are what make the winds so destructive.
The Santa Ana Winds come from the Rocky Mountains and build across the Southwestern United States, specifically Utah, Arizona and Nevada. In this meteorological phenomenon, “drainage winds” blow down the Rockies because of rising air pressure in the mountains’ high elevation and cold climate. This drainage wind builds speed on its descent and gathers heat as the air is compacted by building pressure. This compaction is referred to as “adiabatic heating” and the air both warms and dries out. While these winds do not create fires, they transport the flames vast distances and intensify fires by increasing the amount of available oxygen. The winds may even ignite embers from existing fires, causing fires to be more intense and harder to put out. Coupled with the fact that the winds can reach hurricane speeds, it is no wonder these winds have earned the name “The Devil Winds.”
The station fires in Los Angeles county is not immune to the Santa Ana winds. This past fall, Santa Ana winds swept through the Angeles National Forest at the same time as many wildfires. These winds were measured to be up to 45 miles per hour. The fire was caused by a suspected arson and over the course of over a month, the fires went on to consume over 160,000 acres, 89 homes, and kill 2 firefighters. Massive evacuations were carried out as the winds lowered humidity and increased the combustibility of the area’s vegetation. The fire did not become fully contained until late September. Several smaller fires in the Angeles National Forest and San Gabriel National Forest were also intensified by the winds.
The maps I have created show the varying aspects to this year’s wildfires. The 3D maps show the Rocky Mountains and the Angeles National Forest and the desert basin to its East. This basin lies between the Rockies and the San Gabriel Mountains and makes up the Mojave Desert. The Rockies are where the winds originate and fall (down the western side) becoming compressed and adiabatic heating occurs. The desert is where the winds gain speed and travel towards California. The San Gabriels are home to the Angeles National Forest where the fires were widespread this fall. The Population map shows how densely populated the surrounding areas of the Angeles National Forest are. Population is shown via number of occupied housing units per census tract. You can see that the highly occupied areas fall close to the 210 freeway right up to the edge of most of the forest. Lastly, I included a vegetative cover map that I found on the internet of Los Angeles County. This map shows how much chaparral cover there is in these forests. Chaparral and grasses are the fuel for these fires, as they are the most readily combustible. Especially in times of drought like we are now, this sort of vegetation is extremely flammable.
These maps I feel, clearly demonstrate how the Santa Ana Winds are formed, spread, and how they affect the surrounding population. While the GIS data of vegetation and population help show people things like where to build or buy homes, the main purpose of my blog entry was to show the propagation of the Santa Ana Winds. The map of the Mojave and San Gabriels show how the gusts are channeled through the canyons of the San Gabriels, feeding fires oxygen and enabling them to spread. In the future, I believe that in order to prevent such devastating fires, Californians must be more careful about water usage and land cover. The increased drought and spread of non native grasses has led to fires that occur much more regularly and that are harder to extinguish. The reestablishment of native plants along with water conservation would yield smaller, less frequent fires.
3D Image of Mojave Desert and San Gabriel Mountains
3D Image of the Western Slope of the Rocky Mountains (shows steepness)
Slope DEM of Rocky Mountains (shows steepness)
Number of Occupied Housing Units Surrounding Angeles National Forest
Vegetation Types and Cover of Los Angeles County
For larger sized image: http://frap.cdf.ca.gov/webdata/maps/los_angeles/fvegwhr_map.19.pdf
References:
CBS News. "Santa Ana Winds Drive California Wildfires." CBS Broadcasting Inc. Associated Press, 2009. Web. 23 Sept 2009 <http://www.cbsnews.com/stories/2009/09/23/national/main5330934.shtml>.
Infoplease.com. "Santa Ana Winds."Information Please Database. Liz Olsen, 2009. Web. 2007
IUPAC Gold Book. "Adiabatic Lapse Rate." Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). <http://goldbook.iupac.org/A00144.html>.
KCAL 9. "Station Fire Crews Brace for Santa Ana Winds." CBS Broadcasting Inc. Associated Press, 2009. Web. 21 Sept 2009 <http://cbs2.com/firewatch/Station.fire.Santa.2.1197483.html>.
"Los Angeles County Wildlife Habitats." Map. FRAP: Fire Resource Assessment Program. Sacramento, CA: 2002.
Simply Map. “#Housing, Occupied Units, 2008.” Census 2008 Estimates. UCLA Mapshare Web. 2009.
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