Experimental Investigation of the Energy-Balance of an Alpine Catchment

Water temperature is an important environmental factor which affects the habitat suitability of many fish species and is of central interest for many ecohydrological studies. Over the past 30 years, the scientific community has focused on the understanding and modeling of the mechanisms controlling in-stream temperature. However, the thermal regime of water in the unchanneled state has been poorly studied so far, so that the mechanisms linking precipitation temperature to the water temperature in the stream channel are still unresolved. In particular, existing stream temperature models either rely on direct measurements or on simple correlations with the air temperature to estimate the temperature of stream sources and tributaries. The present study is seen as a first step towards a more physically based computation of such temperatures. The energy balance of a medium-sized alpine catchment (20 km2) is investigated in detail using a set of meteorological and hydrological observations. Particular attention is given to the physical quantities, in particular ground temperature, which affect water temperature in the unchanneled state. The database used for this study was collected over the past six years and contains meteorological data from a high-density network of wireless weather stations, as well as river stage, discharge and temperature measurements. The present work lays the foundations for the future development of an energy balance model at the catchment scale, which will be able to compute the temperature of surface, interflow and baseflow runoffs - and therefore provide some boundary conditions to the actual stream temperature models.