SIMULATING SURFACE AND SUBSURFACE HYDROLOGIC CHANGES ACROSS A RANGE OF GROUNDCOVER CONDITIONS PRODUCED BY FIRE DISTURBANCE

Wildfire activity has increased worldwide due to a combination of fire suppression and climate change. Wildfire activity will increasingly alter ecosystem functions and poses direct and indirect societal dangers including significant hydrologic impacts. This has motivated active wildfire management strategies to reduce risks. However, like wildfire, management options such as prescribed burns can also affect hydrological response by reducing groundcover and increasing the connectivity of overland flow pathways. Models that accurately represent the surface and subsurface interface such as the presence or absence of groundcover components of litter and duff are needed to develop a comprehensive understanding of how wildfire and prescribed fuel treatments affect the surface and subsurface hydrologic response. Here we present two physically-based modeling schemes with in the Advance Terrestrial Simulator (ATS) to represent distinctively different groundcover components of litter and decomposed duff and their impacts on surface and subsurface hydrology. Litter is simulated as an additional vegetative canopy providing increased interception and storage, while increasing surface roughness thereby slowing overland flow. Duff on the other hand is incorporated in the subsurface and therefore has specific hydrologic and water retention properties as well as unique geometries and meshing refinement including pinchouts to resolve infiltration limited runoff generation, run on, and infiltration processes. We further employ sensitivity analysis of the presence of groundcover on 2 and 3D ensembles to investigate the role of surface hydrologic connectivity, i.e. variations of litter and duff patchiness, on the surface and subsurface hydrologic response to precipitation events. The wide-ranging sensitivity analysis then describes the hydrologic response over a large gradient of groundcover conditions covering landscape characteristics produced by high severity wildfire to low intensity fire conditions generated by prescribed burns.