Gravity-Monitoring for Alpine Research Catchment Hydrology

The seasonal snowpack in high-alpine regions plays a significant role for tourism, water and energy supply, and even more so in times of climate change, and is a decisive factor in the development of flood events. A big challenge in alpine hydrology is to improve the spatiotemporal monitoring of water stored in snow (snow water equivalent, SWE) in complex terrain. Current snow measurements are mainly limited to single points, where details on snow depth or SWE are determined via measuring stations. Small-scale SWE derivation with satellites in complex high-alpine terrain is not yet sufficiently possible. In addition to snowpack monitoring, it is important to understand and predict how water, originating from rain or snow and ice melt, moves downwards either on the surface or through soils and rocks and when it reaches the streams, which are not gauged in many catchments. On the German-Austrian peak of the Zugspitze Mountain (2962 m a.s.l.), the German Research Centre for Geosciences (GFZ) is operating the Zugspitze Geodynamic Observatory Germany (ZUGOG) where a high-precision superconducting gravimeter is in operation since the end of 2018. This instrument is capable of measuring the gravitational acceleration at the Earth`s surface with an accuracy of up to 9 decimal places (in textbooks this value is generally given as 9.81 m/s) and provides recordings with a high temporal resolution of up to 1 minute. In addition to determining the precise alpine uplift over many years of measurements, further mass changes within a radius of up to about 4 km can be detected. This encompasses spatiotemporal hydrological mass changes, e.g., due to rainfall or snowfall, snowmelt, infiltration into the underground, evaporation, sublimation, changing ice masses, and even changes in groundwater reservoirs. This worldwide unique installation of a superconducting gravimeter on top of a high-alpine site equipped with an excellent hydrometeorological measurement network and combined with computer simulations in different complexities is used as a novel hydrological monitoring system for the direct, integral and non-invasive observation of the gravity effect of water storage variations. The overarching goal is to investigate to what extent the snow-hydro-gravimetric approach can contribute to a better understanding and quantification of hydrological processes and to be able to transfer potential findings to non-instrumented regions. We also expect to provide important contributions to support future satellite missions in order to enable an enhanced observation of snowpack and water resources on a high-alpine catchment scale worldwide. G-MONARCH is led by the Institute of Hydrology and Water Management at BOKU Vienna in cooperation with the project partners GFZ Potsdam, TU Berlin and Augsburg University. AT: PI: Dr. Franziska Koch Co-PI: Univ.Prof. Dr. Karsten Schulz DE: PI: Prof. Dr. Frank Flechtner Co-PI: Dr. Christian Voigt Co-PI: Apl.Prof. Dr. Karl-Friedrich Wetzel