Hydrological trends and the evolution of catchment research in the Alptal valley, central Switzerland

Abstract

When the observation of small headwater catchments in the pre-Alpine Alptal valley (central Switzerland) started in the late 1960s, the researchers were mainly interested in questions related to floods and forest management. Investigations of geomorphological processes in the steep torrent channels followed in the 1980s, along with detailed observations of biogeochemical and ecohydrological processes in individual forest stands. More recently, research in the Alptal has addressed the impacts of climate change on water supply and runoff generation. In this article, we describe, for the first time, the evolution of catchment research at Alptal, and present new analyses of longterm trends and short-term hydrologic behaviour. Hydrometeorological time series from the past 50 years show substantial interannual variability, but only minimal long-term trends, except for the 2 C increase in mean annual air temperature over the 50-year period, and a corresponding shift towards earlier snowmelt. Similar to previous studies in larger Alpine catchments, the decadal variations in mean annual runoff in Alptal's small research catchments reflect the long-term variability in annual precipitation. In the Alptal valley, the most evident hydrological trends were observed in late spring and are related to the substantial change in the duration of the snow cover. Streamflow and water quality are highly variable within and between hydrological events, suggesting rapid shifts in flow pathways and mixing, as well as changing connectivity of runoffgenerating areas. This overview illustrates how catchment research in the Alptal has evolved in response to changing societal concerns and emerging scientific questions.

Short‐term dynamics of drainage density based on a combination of channel flow state surveys and water level measurements

“…Previous research reported a high similarity in the discharge regimes between the Alp river and its upstream torrents, one of which is the Erlenbach (Staehli et al, 2021). This finding has important implications As expected, using only five or fewer surveys in the CEASE method resulted in lower accuracy and sensitivity for both catchments (Figure 5).…”

“…This study was carried out in two sub‐catchments of the pre‐Alpine Erlenbach research catchment (Staehli et al, 2021; Figure 1): Langried (Lan) and Chaspersböden (Cha). The Erlenbach catchment (Erl) has an area of 0.7 km 2 and ranges in elevation from 1080 to 1520 m a.s.l.…”

“…The average annual precipitation at 1210 m a.s.l. in the Erl catchment is 2266 mm (water years 1969–2019; Staehli et al, 2021). Snowfall represents a third of the total precipitation.…”

“…Water levels were measured at this location using pressure transducers and recorded by digital Philips and Campbell dataloggers. The stage-discharge relationship was obtained by salt-dilution measurements (Staehli et al, 2021).…”

Four years of daily stable water isotope data in stream water and precipitation from three Swiss catchments

“…A detailed description of the long-term hydrometeorological measurements in the Alptal catchment is provided by Stähli et al . 23 .…”