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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-604
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
01 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Assessing the long-term hydrologic response to wildfires in mountainous regions
Aaron Havel1,2, Ali Tasdighi1,3, and Mazdak Arabi1 1Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523, USA
2AWR Engineering, LLC, Anchorage, AK 99519, USA
3Department of Civil and Environmental Engineering, University of California Irvine, Irvine, CA 92697, USA
Abstract. This study aims to understand the long-term hydrologic responses to wildfires in mountainous regions at various spatial scales. The Soil and Water Assessment Tool (SWAT) was used to evaluate hydrologic response of the upper Cache la Poudre watershed in Colorado to the 2012 High Park and Hewlett wildfire events. A baseline SWAT model was established to simulate the hydrology of the study area between the years 2000 and 2014. The effects of wildfires on land cover were accounted for in the model using the SWAT land use update module. The wildfire effects on curve numbers were determined comparing the probability distribution of curve numbers after calibrating the model for pre and post wildfire conditions. Daily calibration and testing of the model produced very good results. No-wildfire and wildfire scenarios were created and compared to quantify changes in average annual total runoff volume, water budgets, and full streamflow statistics at different spatial scales. At the watershed scale, wildfire conditions showed little impact on the hydrologic responses. However, a runoff increase up to 75 percent was observed between the scenarios in sub-watersheds with high burn intensity. Generally, higher surface runoff and decreased subsurface flow were observed under post-wildfire conditions. Flow-duration curves developed for burned sub-basins using full streamflow statistics showed that less frequent streamflows become greater in magnitude. A strong (R2 > 0.8) and significant (p < 0.001) positive correlation was determined between runoff increase and percentage of burned area upstream. This study showed that the effects of wildfires on hydrology of a watershed are scale-dependent. Results also revealed that the wildfires had a higher effect on peak flows, which may increase the risk of flash floods in post-wildfire conditions.

Citation: Havel, A., Tasdighi, A., and Arabi, M.: Assessing the long-term hydrologic response to wildfires in mountainous regions, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-604, in review, 2017.
Aaron Havel et al.
Aaron Havel et al.
Aaron Havel et al.

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Short summary
This study investigated the hydrologic responses to wildfires in mountainous regions using a watershed model. The results indicate that while at the watershed outlet the changes in hydrologic responses may not be significant, at subwatersheds with high burn intensity runoff increase up to 75 % was observed after the wildfire. Also, the chance of more severe floods was increased. The results have important implications for post-wildfire water resources planning and precautions for flash floods.
This study investigated the hydrologic responses to wildfires in mountainous regions using a...
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