Modelling the impact of land use changes on peak discharge in the Urseren Valley, Central Swiss Alps

In alpine regions, global climate change will likely alter rain and snowfall patterns and increase the frequency of extreme meteorological events such as floods. These events, combined with land use changes, may pose an immediate hazard to the life and properties of downslope inhabitants and to water resource structures downstream. The aim of this study is to evaluate the impact of land use changes (e.g., areas covered by grassland, green alder, and dwarf shrubs) on peak discharge for different return periods and different scenarios (past, current, and future) in the Urseren Valley in the Central Swiss Alps. In addition to the entire Urseren Valley, we also considered four microcatchments of various sizes and land covers within the valley. We used the ZEMOKOST model, which considers the impact of a wide range of vegetation and channel characteristics on surface hydrology. Results at the catchment scale show an increase in peak discharge for all return periods from 2 to 300 years. In two microcatchments, simulation results indicate that expected changes in the vegetation cover will drastically decrease peak discharge in the future for all return periods, by up to 41% (for a 100-year return period). At the catchment scale, although the surface area covered by green alder increases by 38% and the area covered by dwarf shrubs decreases by 26% from the current to the future scenario, the peak discharge increases for all return periods except for the 2- and 5-year return periods. It appears that the drastic decrease of grassland area from the current to future (− 52%) scenario is responsible for the slight increase in peak discharge (about 4% for a 100-year period). In addition, surface area covered by dwarf shrub not only decreases from the current to future scenario, but also clusters into more continuous zones damping lateral flow and resulting in such moderate increase. The consistency between observed and simulated peak discharge for a 100-year return period attests the reliability of our modelling outcomes. Careful land use planning taking into account the results of our analysis can help to better manage land and water resources in the region.