Comparison of Runoff characteristics in bare and vegetated headwater catchments, Northern Alps, Japan

We evaluated an effect of alpine vegetation on water storage and runoff characteristics in alpine zones. We sampled rainwater, snowmelt water and runoff water from bare and vegetated catchments in August and October 2019 in headwater catchment of Mt. Norikura, Japan. We compared the water chemistry of runoff water from bare catchments and vegetated catchments. The pH, electrical conductivity and total dissolved ion concentrations of runoff water from vegetated catchments were higher than those from bare catchments, suggesting a longer contact time between water and the regolith in the vegetated catchments. We also applied two-component hydrograph separation to calculate the contribution of precipitation and groundwater components to the runoff water. The contribution of groundwater component to runoff water ranged from 0.8% to 63.8% in the vegetated catchments, whereas that ranged from 0.3% to 14.6% in the bare catchments. Furthermore, the groundwater contribution was higher in the area with vegetation predominantly over the bare area in each catchment. This suggests that the runoff water has longer transit time in the vegetated areas than the bare areas. In the vegetated areas, the subsurface water should flow with longer transit time due to an existence of well-developed regolith with coarse-grained sediments as compared with that in bare areas. Thus, the alpine vegetated area has a higher water storage function than the bare area. Our results show that we need to consider the vegetation and regolith conditions and subsurface flow processes to the hydrological processes in mountainous areas, especially in alpine zones.