River water temperature is one of the main drivers of water quality in rivers. Due to climate and anthropogenic land use changes, mean river water temperature has risen over the last 30 years, especially at high elevations as smaller streams are affected more strongly by changes in atmospheric forcing and snow influences. While information on small-scale variability of water temperature and its drivers is crucial for better process understanding, existing research has mainly focussed on rivers where only one temperature measuring station is available. This study aims to improve the understanding of small-scale water temperature variability and its hydro-climatic drivers by conducting an extensive 3-year field campaign in a catchment in the Swiss Alps.

To this aim, we measure water temperature, discharge, air temperature, and relative humidity at 15 locations within the alpine Dischmá catchment (Switzerland) along a strong elevational gradient from 1500 – 2500 m a.s.l. First, we describe the diurnal, monthly and annual variability of water temperature at different elevations to understand how water temperature variability changes along an elevation gradient. Second, we use the high spatial resolution of our measuring setup to assess the effect of lakes, glacier ice and snowmelt on water temperature. Third, we investigate the relative importance of cryospheric, hydrological, and atmospheric drivers in the development of seasonal temperature anomalies using additional spatial data of groundwater bodies. Our preliminary results show a strong diurnal water temperature cycle and a dampening influence of groundwater influx on the diurnal water temperature amplitude and indicate that the diurnal valley winds may cool the river.

Our improved understanding of river water temperature at high altitudes will support efforts to counteract the negative ecological and economic impacts of warming mountain rivers.