Stream temperature and discharge evolution in Switzerland over the last 50 years: annual and seasonal behaviour

Abstract

Abstract. Stream temperature and discharge are key hydrological variables for ecosystem and water resource management and are particularly sensitive to climate warming. Despite the wealth of meteorological and hydrological data, few studies have quantified observed stream temperature trends in the Alps. This study presents a detailed analysis of stream temperature and discharge in 52 catchments in Switzerland, a country covering a wide range of alpine and lowland hydrological regimes. The influence of discharge, precipitation, air temperature, and upstream lakes on stream temperatures and their temporal trends is analysed from multi-decadal to seasonal timescales. Stream temperature has significantly increased over the past 5 decades, with positive trends for all four seasons. The mean trends for the last 20 years are +0.37±0.11 ∘C per decade for water temperature, resulting from the joint effects of trends in air temperature (+0.39±0.14 ∘C per decade), discharge (-10.1±4.6 % per decade), and precipitation (-9.3±3.4 % per decade). For a longer time period (1979–2018), the trends are +0.33±0.03 ∘C per decade for water temperature, +0.46±0.03°C per decade for air temperature, -3.0±0.5 % per decade for discharge, and -1.3±0.5 % per decade for precipitation. Furthermore, we show that snow and glacier melt compensates for air temperature warming trends in a transient way in alpine streams. Lakes, on the contrary, have a strengthening effect on downstream water temperature trends at all elevations. Moreover, the identified stream temperature trends are shown to have critical impacts on ecological and economical temperature thresholds (the spread of fish diseases and the usage of water for industrial cooling), especially in lowland rivers, suggesting that these waterways are becoming more vulnerable to the increasing air temperature forcing. Resilient alpine rivers are expected to become more vulnerable to warming in the near future due to the expected reductions in snow- and glacier-melt inputs. A detailed mathematical framework along with the necessary source code are provided with this paper.

Real‐time warming of Alpine streams: (re)defining invertebrates' temperature preferences

“…The averaged warming rate of studied streams during the last years (0.25°C per year, 80% CI 0.19–0.32°C) is considerably higher than that of local air temperature and the recently observed and modelled warming of Swiss streams in alpine settings (Michel, Brauchli, Lehning, Schaefli, & Huwald, 2020). This long‐term survey over 40 years revealed an average slope of +0.33°C per decade for Swiss streams with diverse catchment topography, elevation and size.…”

A Framework for Untangling Transient Groundwater Mixing and Travel Times

“…Michel et al. (2020), for example, found that between 1999 and 2018 the annual discharge of the Emme already decreased each decade by 12% ± 4%. Additionally, Addor et al.…”

Current and projected impacts of the parasite Tetracapsuloides bryosalmonae (causative to proliferative kidney disease) on Central European salmonid populations under predicted climate change

“…The future impact of PKD on brown trout, grayling, and salmon populations is greatly dependent on how water temperature, precipitation, and evaporation change in the context of the climate crisis (Borgwardt et al., 2020; Masson‐Delmotte et al., 2018). Water temperatures in central Europe have already increased by 1–2°C (Daufresne & Boët, 2007; Kędra, 2020; Michel et al., 2020; Webb & Nobilis, 2007) and patterns of precipitation have changed in quality (increasingly torrential rain, less snow) and seasonality (decreases in summer, increases in winter) (Masson‐Delmotte et al., 2018). Under these conditions, salmonids are estimated to have already lost half of their population density (Arndt et al., 2019; Burkhardt‐Holm & Zehnder, 2018; Waldner et al., 2020).…”