Exploring diel streamflow variations in an alpine headwater catchment

During rain-free periods, and in catchments without considerable human intervention, diel streamflow cycles are characterized by distinctive patterns of rising and falling streamflow over the course of day. This dynamic is mainly driven by variations in solar radiation leading to an impact of snow and glacier melt, and evapotranspiration (ET) on diel streamflow cycles in alpine catchments. However, there are also other processes such as thermal expansion of water and streamflow-groundwater exchange that can lead to variations in diel streamflow patterns.

In this study, we investigate diel streamflow cycles in the 12 km² sized Fundusbach headwater catchment of the Ötztaler Ache in the Eastern European Alps. Based on observation data from three water level loggers along the longitudinal river profile (installed in 2022), we aim to identify the relative role of meltwater, ET, and water temperature on diel streamflow cycles along the river profile to better understand the interaction of these ecohydrological processes both spatially and seasonally. Results reveal that throughout the year without snowfall, diel streamflow cycles are mainly driven by meltwater dynamics. However, isolating the meltwater impulse from the uppermost part of the catchment from the water level loggers further downstream, diel streamflow cycles highlight the potential influence of ET. In the next step, we aim to correlate these streamflow variations with water temperature to quantify the effects of thermal expansion and the potential impact of water exchange between streamflow and soil- and groundwater.