Hydrological trends for three headwater catchments in the Alptal valley, Switzerland

Hydrological research in the Alptal valley in central Switzerland started in the late 1960s and has mainly focused on the runoff mechanisms that lead to the very quick runoff response, the relation between forest management and floods, biogeochemistry and nutrient cycling, and sediment transport. Current research in the Alptal includes the assessment of the impacts of climate change on low flows and peak flows. In this poster, we will describe the research catchments and present the results of recent trend analyses for three headwater catchments. The hydro-meteorological measurements over the last 50 years indicate that there is considerable inter-annual variability in rainfall, snow cover, and streamflow. The approximately 2°C increase in mean annual air temperature has led to a shorter period with snow cover and an earlier snowmelt, a decrease in streamflow in May, and an increase in streamflow in January and March. The number of dry summers is still small (2003, 2015 and 2018) but they have all occurred in the last 20 years. The coefficient of variation of streamflow and the Richard-Baker flashiness index suggest that both the day to day and overall variability in streamflow is increasing, which motivates us to continue our studies on runoff generation and storage dynamics in the study catchments.