Subsurface hydrological connectivity of vegetated slopes: a new modeling approach

Abstract. Vegetation strongly influences the hydrology of hillslopes through different processes that may be important for the mitigation of flood risks. The complicated interactions of mechanisms that contribute to the formation of runoff at different spatial and temporal scales represent a big challenge for catchment hydrology. However, it is recognized that storage capacity and infiltration are one of the most important processes positively influenced by vegetation. Moreover, numerical studies have discussed the importance of preferential subsurface flow as dominant processes contributing to fast runoff in mountain catchments. While, previous studies have shown the importance of bedrock topography on the connectivity and drainage of shallow soil mantled hillslopes, no studies discussed the role of heterogeneous root distribution on the drainage of hillslope with stagnic soils so far. In this work we present a conceptual model that aims to link modelling approaches of root distribution combined to hydrological modelling of preferential flow, and the quantification of hydrological connectivity of forest hillslopes. We use a spatial distributed root distribution model to calculate the number of fine roots based on the structure of forest cover (tree position and dimension). The results of root distribution are used as input parameter for the quantification of preferential flow patches using a numerical approach. Finally, we use the spatial distributed values of preferential flow to calculate the hydrological connectivity of a vegetated hillslope considering topography and soil profile characteristics. The new proposed framework is calibrated through field experiments at the soil profile scale, and the first results of the numerical simulations considering different combination of parameters are discussed in the context of protection forests mitigation effects against flood risks.