Spatial and temporal variation in soil moisture and transpiration in the Studibach catchment, Switzerland

Transpiration is a key process of the water cycle and is influenced by various ecosystem factors. The interplay between the different factors, especially between soil moisture and transpiration, is not fully understood. On top of that, climate change is expected to shift water fluxes by decreasing runoff and increasing evapotranspiration in the pre-Alpine region, with implications for local forest health and water supplies for downstream basins. Therefore, this thesis contributes to the understanding of the temporal and spatial variation of soil moisture and transpiration, across a hillslope. The study was conducted in the Studibach catchment in the Alptal in the pre-Alpine region of Switzerland, during the growing season of 2024. Sap flow of Norway spruce trees was measured at three locations across a slope. At additional location’s manual and continuous soil moisture measurements as well as the meteorological conditions were recorded, and sap wood area was estimated from tree cores. Findings show a weak correlation between soil moisture and topographic wetness index. During moderate soil moisture conditions, the correlation is stronger between soil moisture and the topographic wetness index, in comparison to wet conditions. Sap flow was shown to significantly differ between sites with different topographic wetness index at a monthly scale and partially on a weekly scale. Meanwhile transpiration shows a different spatial pattern which is due to the amount of sapwood area per site. For both sap flow and transpiration, a difference across the study sites is found but the explanation for the spatial pattern remains unclear. It is recommended to extend the research with measurementsin a dry year and more locations.