Introduction
Location Map
Base Map
Database Schema
Conventions
GIS Analyses
Flowchart
GIS Concepts
Results
Conclusion
References
Introduction
~ Wildfire Occurrence and Potential Erosion Within the Cache La Poudre Watershed, 2003-2012 ~
By Andrew Spencer and Emma Vakili
The final project for our graduate level Geographic Information Systems course was done in cooperation with the Colorado State University Headwaters Initiative. In pairs, we were directed to analyze some feature of the Cache La Poudre River watershed of northern Colorado. Our group consisted of Andrew Spencer and Emma Vakili, both of us are current M. S. Forest Science students in the Department of Forest and Rangeland Stewardship within the Warner College of Natural Resources.
Being forestry graduate students that have both worked in wildland fire science, we decided to analyze the occurrence of wildfires in the Poudre River watershed during the ten-year period from 2003 to 2012. Very little spatial data was found describing the burned area perimeters for small fires, which are by far the majority of incidents. To address this, we took the available point data from the US Geological Survey and created buffers of each point that represents the total acres burned for all fires under 1,000 acres in size, resulting in circles that approximate the actual size of each of these small fires (though not necessarily the exact shape). Perimeters were available for all fires over 1,000 total acres in the study area, and these files were used in the final maps.
We used a variety of scholarly journal articles about fire effects in Colorado to establish the parameters for our analysis, eventually settling on slope, aspect and proximity to water to establish zones of highest risk for post-fire erosion and fire severity over the 12 year period, but based on our research (listed under the References section), we found that northern aspects with a slope of over 30% posed the highest risk for severe fires and post fire erosion. Northern aspects, in general, have the highest fuel loadings that result in the highest levels of soil impact following a fire. Based on this we created a risk map for our analysis with four levels:
- Low Risk: Southern Aspects <30% Slope
During the course of our preliminary research, we also found that post fire erosion is most significant for the three to four years following a fire. This means that the erosion in 2010 would likely be impacted by the fires that occurred in 2007, 2008, 2009 and 2010, while burn areas prior to 2007 would probably have recovered enough vegetation to negate the worst of the erosion. Identifying an appropriate buffer zone for streams is difficult because in reality, the risk zone depends on the complex relationship between soil type, vegetation type, slope, aspect, and proximity first of all, and then the severity of the wildfire afterwards. That being said, the Arapaho Roosevelt Forest Plan (1997 revision), suggests that a 300 foot buffer on each side of streams containing threatened or endangered species be of special concern for the maintenance of hydrological function. We have used this recommendation to identify zones of special concern along all of the rivers and streams in the watershed to better capture the total risk zones.
Using this background information, we analyzed the total burned area for the four year period leading up to each year in the ten year period from 2003 to 2012 and overlayed these fires with our risk map. We created a series of maps to show this change and a graph of our results.
The High Park Fire burned a large amount of the Cache La Poudre Watershed in 2012
Photo by Karl Gehring, The Denver Post
