Meltwater temperature in streams draining Alpine glaciers.

Climate change is significantly impacting lotic environments, through changes to hydrology, biodiversity and species distribution. Effects of climate change are greatest at high elevation and biota in and around glacier-fed rivers is likely, therefore, to be at great risk. How climate change influences hydrology will have great impact on river water temperature as glacier-fed rivers in Alpine environments are extremely sensitive to climatic change. This paper assesses five rivers: Four glacier-fed rivers (36.9-83.7% basin glacierisation) located in the Swiss Alps, and one located in an ice-free catchment in the Bernese Oberland, Switzerland. The aim was to assess the impact of basin characteristics on river water temperature. A distinct paradoxical relationship was identified whereby water temperature in some glacier-fed rivers was reduced during the time of highest incoming shortwave radiation receipts and high air temperature. Whether a summer cooling effect presented itself in all glacier-fed rivers within this study was researched. The key findings were that the identified summer cooling effect was not present in all rivers, despite percentage glacierisation. Percentage glacier cover has often been reported as they key determiner of water temperature in such rivers. More important was the stream dimensions, notably stream surface area. Understanding the controlling factors that influence water temperature of glacier-fed rivers will help river managers and planners in understanding how climate change will affect fisheries downstream of glaciers over the coming decades. This may allow plans to be introduced to try and mitigate warmer water temperature that will result, in some glacier-fed rivers, as the climate warms.