Water temperature of Alpine streams in response to discharge and radiation

Pea, GC

Abstract

The aim of this study is to examine the relationships between water temperature, discharge and their response to shortwave radiation in a highly glacierised Alpine basin. Due to the high altitude, the Alps have one of the highest solar radiation budgets in Europe and demonstrated almost double the rate of warming of the Northern Hemisphere. Understanding the effect radiation has on stream temperature is key as this is the primary control on water quality due to its influence on chemical, biological and physical processes. Studies of the Aletschgletscher basin have highlighted a paradoxical relationship between water temperature and air temperature; however there is limited research on the relationship between water temperature and solar radiation, which is of importance as radiation is the primary energy input (up to 80%) to Alpine proglacial streams. The river Massa in Canton Valais, Switzerland is the study areas, where the highly glacierised basin (65.9%) from which the rivers are sourced has shown high sensitivity to climatic warming. This is evident as Aletschgletscher has been recorded (2003) to be retreating by 20m a year. Hydrological data acquired from FOEN and shortwave radiation from Zermatt were analysed at high and low resolutions for the spring, summer and autumn. As expected seasonal runoff and radiation trends correlate with a lag time of up to 6 weeks between their peaks (2012), and water temperature has shown the paradoxical trend in summer; when radiation is at its highest levels water temperature decreases. This corresponds with the early ablation period when levels of discharge begin to increase, extending the cool tongue of water. During the ablation season water temperature has the highest range and undergoes periods of warm surges though radiation is still low. Stream temperature decreases from its peak at a high rate as discharge increases from the winter minima of approximately 0.5 m3s−1 to 3.5 m3s−1. While flow level is relatively low it proves to be the tipping point and demonstrates how radiation has a positive correlation with water temperature in spring but a negative correlation in summer due to the increased runoff. The years 2003-2012 have shown water temperatures to peak between 1 April and 12 May, up to 2 months prior to radiation peaks. The implications of these findings are that water quality will deteriorate as stream flow decreases.

Citation

Pea, G. (in press). Water temperature of Alpine streams in response to discharge and radiation. (Dissertation). University of Salford

• Thesis Type: Dissertation
• Acceptance Date: Oct 1, 2017
• Deposit Date: Feb 23, 2018
• Publicly Available Date: Feb 23, 2018