This week, for my final mini-project, I explored data on the internet indicating the various locations and dates of LA County fires from August to September, 2009. I then input this data into Arc Map and utilized my knowledge of vectors and GIS modeling to create one reference and two thematic maps. I chose to display elevation and slope, and imported the DEM into my blog for you all to see! What I analyzed was the effects of topography, specifically slope and elevation, on the spread of fires in LA County.
It is pretty apparent from my DEM that the fire spread increases and covers more area with increasing elevation. This is suggested by the contour lines, which illustrate that, for the fires that covered more surface area, the elevation was of mid to high level. This finding is actually quite interesting, because it contradicts the general trend of decreasing rates of fire spread with increasing elevation.
Generally, elevation influences temperature, precipitation, and humidity. The consequence of this is its influence on fuel availability. However, at mid-elevations, thermal belts can occur. This causes the warm air to become trapped below cold air at any elevation level, and tends to happen at night. My thematic map illustrating elevation then suggests that thermal belts might have been the cause of increasing fire spread with increasing elevation.
I additionally looked into the effect of slope on fire spread. Slope affects fire in the same manner as wind. Slope’s influence on the flame angle results in combustibility and an increase in the rate of fire spread. This general trend is pretty consistent with my DEM, as the largest fires occurred with slopes in the yellow/red category (moderate to high slope levels).
While my hypothesis about the pattern of thermal belts may or may not be correct, it is definitely apparent that my DEM negates preconceptions of elevation’s affect on fire spread. At the same time, it is consistent with the findings presented on my map of the slopes, indicating that there was no interference with its consequential effect on flame angle and combustibility. I now have a better understanding of how GIS can be utilized to either confirm (or dispute) an accepted trend in environmental occurrences. Maybe it will help Smokey prevent some forest fires (or LA county ones) in the near future!
Works Cited
"DEM Derivative: Slope Gradient and Aspect." UBC Department of Geography. Web. 09 Dec. 2011.
<http://www.geog.ubc.ca/courses/geog570/talks_2001/slope_calculation.html>.
<http://www.geog.ubc.ca/courses/geog570/talks_2001/slope_calculation.html>.
"Effects of Topography on Fire Intensity and Rate of Spread —
Forest Encyclopedia Network." Encyclopedia Collection — Forest Encyclopedia Network. Web. 09 Dec. 2011.
<http://www.forestencyclopedia.net/p/p489>.
Gesch, Dean. "Fact Sheet 2009-3053: The National Map-Elevation." USGS Publications Warehouse. Web. 08 Dec. 2011.
<http://pubs.usgs.gov/fs/2009/3053/>.
"GIS Manual: Spatial Information in Design Culture." HarvardUniversity Graduate School of Design. Web. 08 Dec. 2011.
<http://internal.gsd.harvard.edu/gis/manual/dem/>.
"USGS SDTS Format Digital Elevation Model Data (DEM)." FreeGIS Data - GIS Data Depot. Web. 09 Dec. 2011.
<http://data.geocomm.com/dem/>.