Water study

93% of Alpine water is older than one month

It shows that more old water tends to be found in areas that are higher, steeper and characterized by large differences in altitude, which have a large water storage volume. In the photo: River in Brandnertal

(Bild: Ilhan Balta - stock.adobe.com)

An Austrian-Swiss research team has analyzed how much time passes from the time it rains until it flows into Alpine rivers. 

According to the University of Natural Resources and Life Sciences (Boku), the proportion of water that is older than one month is around 93 percent across the 32 areas studied. This "old water paradox" shows once again how important natural reservoirs are.

32 catchment areas in the Alpine region
The focus was on a total of 32 catchment areas in the Alpine region. From Austria, long-term isotope data from the Danube (Hainburg, Engelhartszell and Wien-Nußdorf), the Drau (Neubrücke), the Leitha near Brodersdorf, the March near Angern, the Inn (Schärding and Kirchbichl), the Salzach near Salzburg, the Mur near Spielfeld, the Ill near Gisingen and the Rhine near Lustenau were included.

The analysis in the journal "Hydrology and Earth System Sciences" distinguishes between "new water" (less than one month old) and "young water" (two to three months old) in Alpine rivers. The proportion of new water in the discharge is low at 3.5 to 9.6 percent, while young water is around twice as common.

However, most of the water in these rivers is older and comes from underground reservoirs. This old water is displaced and released by new precipitation or meltwater. The study emphasizes the importance of soil and groundwater reservoirs in cushioning floods, which are endangered by soil sealing.