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Other publication (non peer-review)

Book Impact of snow on drought Intensification of isotope sampling in streamflow and precipitation in the Alptal: design and first evaluation
Publisher ETH Zürich Master Thesis, Zürich

Abstract

It is now well established that the surface temperature in Switzerland has undeniably increased by around 1.5_C over the last 100 years, consequently both the permanent and seasonal snow covers have witnessed stark decrease in their sizes and volumes. Although snowmelt contributes 40% of Swiss runoff, the relationship between snowmelt and runoff remains poorly understood. In order to better understand this relationship, a multi-national multi-disciplinary project named Snow Resources and Early Prediction (SREP) of Drought was launched in 2015. Its aims are to improve the calibration and prediction of rainfall-runoff generation models by analysing the relationship between summer flows and winter snowpacks in Switzerland, Georgia and the Czech Republic by using environmental isotope tracer hydrology. The chosen catchment in Switzerland for this project is the Alptal Valley, where meteorological and hydrologic monitoring have been taking place for over a half century, which could be used to analyse long term trends in snow, precipitation and runoff. This master thesis focuses on the setup and preliminary analyses of the isotopic monitoring network in the Alptal valley, namely the collection frequency, size of the collecting funnels and evaporation limitation techniques of the new hydrological installations. Using a combination of past data and the fruit of the newly set up network, the isotopic signature of the meteoric waters was defined for the Alptal valley. The link was made between the long-term quantitative trends and the isotopic signature of snow, precipitation and runoff to show how isotopes correlate with the snow, humidity, precipitation and temperature of the valley and can be successfully used to trace the journey of meteoric water though the catchment area. It was found that the composition of all meteoric waters (snow, precipitation and runoff) in the valley responded most sensitively to temperature change, which seemed to be the main defining factor of isotopic composition. Furthermore, there was a considerable level of spatial variation of isotopic signature of meteoric waters. This indicated that primary vapour sources and secondary evaporation during rainfall vary within the valley with increasing distance from the high mountain ranges. Finally, strong correlations between runoff and precipitation with the snowpack of the given year were found throughout spring and summer, both with isotopic signature and runoff and snow quantity. The results suggested that the mean snow depth in winter impacted the timing of isotopic depletion of runoff all along the Alptal valley, as well as the extent of winter depletion and summer enrichment. These results show that isotopic monitoring in the Alptal valley have the potential of better understanding the journey from snowmelt to runoff, which will allow the SREP Drought project to use snow depth information to predict periods of lower flow.
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