The thermal future of a regulated river: spatiotemporal dynamics of stream temperature under climate change in a peri-Alpine catchment

Abstract

Climate change is driving an increase in river water temperatures, presenting challenges for aquatic ecosystems and water management. Many rivers are regulated by hydropower production, which alters their thermal regimes, causes short-term temperature fluctuations (thermopeaking) linked to flow variations, and whose future evolution under climate change remains uncertain. This study examines how the thermal regime of a peri-alpine regulated river could evolve under future climate scenarios using a high-resolution process-based model. Projections indicate that mean annual water temperatures may rise by up to 4 °C by 2080–2090 under RCP 8.5, with daily mean temperatures exceeding 15 °C for nearly half the year, raising ecological concerns. While these trends are comparable to those in unregulated rivers, river regulation introduces distinct spatial and seasonal patterns in climate change impacts. The reach with only a residual flow is particularly susceptible to warming due to limited discharge, whereas deep reservoir releases help moderate climate change impacts downstream of the dam and the hydropower plant. Furthermore, unlike in unregulated rivers where the strongest warming typically occurs in summer, climate change impacts in this regulated system are projected to be most pronounced in autumn and winter due to the thermal inertia of the reservoir. Indicators used to assess thermopeaking impacts remain largely unaffected by climate change, provided that hydropower operation remains unchanged. This study highlights that while regulation can exacerbate vulnerabilities to climate change, it also mitigates climate change impacts by influencing river temperature dynamics beyond thermopeaking alone.