The timing and magnitude of changes to Hortonian overland flow at the watershed scale during the post-fire recovery process

Taojun Liu; Luke A. McGuire; Haiyan Wei; Francis K. Rengers; Hoshin Gupta; Lin Ji; David C. Goodrich

doi:10.1002/hyp.14208

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The timing and magnitude of changes to Hortonian overland flow at the watershed scale during the post-fire recovery process

Taojun Liu·Luke A. McGuire·Haiyan Wei·Francis K. Rengers·Hoshin Gupta·Lin Ji·David C. Goodrich

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Abstract

Extreme hydrologic responses following wildfires can lead to floods and debris flows with costly economic and societal impacts. Process-based hydrologic and geomorphic models used to predict the downstream impacts of wildfire must account for temporal changes in hydrologic parameters related to the generation and subsequent routing of infiltration-excess overland flow across the landscape. However, we lack quantitative relationships showing how parameters change with time-since-burning, particularly at the watershed scale. To assess variations in best-fit hydrologic parameters with time, we used the KINEROS2 hydrological model to explore temporal changes in hillslope saturated hydraulic conductivity ( K sh ) and channel hydraulic roughness ( n c ) following a wildfire in the upper Arroyo Seco watershed (41.5 km 2 ), which burned during the 2009 Station fire in the San Gabriel Mountains, California, USA. This study explored runoff-producing storms between 2008 and 2014 to infer watershed hydraulic properties by calibrating the model to observations at the watershed outlet. Modelling indicates K sh is lowest in the first year following the fire and then increases at an average rate of approximately 4.2 mm/h/year during the first 5 years of recovery. The estimated values for K sh in the first year following the fire are similar to those obtained in previous studies on smaller watersheds (<1.5 km 2 ) following the Station fire, suggesting hydrologic changes detected here can be applied to lower-order watersheds. Hydraulic roughness, n c , was lowest in the first year following the fire, but increased by a factor of 2 after 1 year of recovery. Post-fire observations suggest changes in n c are due to changes in grain roughness and vegetation in channels. These results provide quantitative constraints on the magnitude of fire-induced hydrologic changes following severe wildfires in chaparral-dominated ecosystems as well as the timing of hydrologic recovery.

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Water Resources Research Article

Source-reported bounding extent: 33.88865750124072° to 34.96699890670367° latitude; -118.68530273437499° to -116.27929687499999° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Taojun Liu, Luke A. McGuire, Haiyan Wei, Francis K. Rengers, Hoshin Gupta, Lin Ji, David C. Goodrich. 2021-05-27. The timing and magnitude of changes to Hortonian overland flow at the watershed scale during the post-fire recovery process. https://doi.org/10.1002/hyp.14208

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