Abstract
Abstract. River ecosystems are highly sensitive to climate change and projected future increase in air temperature is expected to increase the stress for these ecosystems. Rivers are also an important socio-economic factor impacting, amongst others, agriculture, tourism, electricity production, and drinking water supply and quality. In addition to changes in water availability, climate change will impact river temperature. This study presents a detailed analysis of river temperature and discharge evolution over the 21st century in Switzerland. In total, 12 catchments are studied, situated both on the lowland Swiss Plateau and in the Alpine regions. The impact of climate change is assessed using a chain of physics-based models forced with the most recent climate change scenarios for Switzerland including low-, mid-, and high-emission pathways. The suitability of such models is discussed in detail and recommendations for future improvements are provided. The model chain is shown to provide robust results, while remaining limitations are identified. These are mechanisms missing in the model to correctly simulate water temperature in Alpine catchments during the summer season. A clear warming of river water is modelled during the 21st century. At the end of the century (2080–2090), the median annual river temperature increase ranges between +0.9 ∘C for low-emission and +3.5 ∘C for high-emission scenarios for both lowland and Alpine catchments. At the seasonal scale, the warming on the lowland and in the Alpine regions exhibits different patterns. For the lowland the summer warming is stronger than the one in winter but is still moderate. In Alpine catchments, only a very limited warming is expected in winter. The period of maximum discharge in Alpine catchments, currently occurring during mid-summer, will shift to earlier in the year by a few weeks (low emission) or almost 2 months (high emission) by the end of the century. In addition, a noticeable soil warming is expected in Alpine regions due to glacier and snow cover decrease. All results of this study are provided with the corresponding source code used for this paper.
Highlights
River systems are considered to be among the ecosystems most sensitive to climate change (CC) (Watts et al, 2015) and the projected future increase in air temperature (IPCC, 2021) is expected to increase the stress for these ecosystems
A chain of physics-based models is used with 21 CC scenarios, spanning three different emission pathways (RCP2.6, RCP4.5, and RCP8.5)
The model chain is applied to two categories of catchments, namely the lowland Swiss Plateau catchments and the higher-elevation Alpine catchments, which exhibit different discharge and thermal regimes
Summary
River systems are considered to be among the ecosystems most sensitive to climate change (CC) (Watts et al, 2015) and the projected future increase in air temperature (IPCC, 2021) is expected to increase the stress for these ecosystems. A. Michel et al.: Future river temperature under climate change ables for aquatic ecosystems, influencing both chemical and biological processes (Benyahya et al, 2007; Temnerud and Weyhenmeyer, 2008). Certain fish species are highly sensitive to warm water, which can promote specific diseases (e.g. proliferative kidney disease, PKD) or prevent reproduction (Caissie, 2006; Carraro et al, 2016), while higher temperatures might be favourable for some other species, enhancing biological invasion (Paillex et al, 2017; Niedrist and Füreder, 2021). In Alpine regions, together with water temperature, glacier retreat is expected to contribute to accelerated changes in ecosystems (Cauvy-Fraunié and Dangles, 2019; Fell et al, 2021)
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