Water in Alpine rivers hardly ever comes from fresh rain
Published: Tuesday, Aug 27th 2024, 08:40
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Fresh rainwater makes up only a small proportion of the water in Alpine rivers. As an analysis by a Swiss-Austrian research team shows, the proportion of water in Alpine rivers that is older than one month is around 93 percent.
A large proportion of the water in the rivers of Alpine regions comes from underground water, i.e. from water stored in the soil and groundwater, as the researchers showed in the study published in the journal "Hydrology and Earth System Sciences".
This knowledge of the origin and age of the water is crucial for assessing the potential risk to water resources, emphasized the Austrian University of Natural Resources and Life Sciences (Boku), which was involved in the study, in a press release on the study. In addition to researchers from Boku, researchers from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) were also involved in the study.
Old water dominates even during floods
According to the analysis, even during floods, on average more than 70 percent of the water in the rivers was still older than one month. In fact, during heavy rainfall, older water that has been stored close to the river courses for longer is displaced and released by the subsequent precipitation or meltwater.
How old water is can be estimated using modern scientific methods by measuring the composition of the stable isotopes in it. For their study, the team led by Marius Floriancic from ETH Zurich and Christine Stumpp from Boku drew on several years of isotope analyses of rainwater and runoff water. In Switzerland, the Aare, Rhone, Sense and Sitter rivers, among others, were analyzed.
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