Non-invasive monitoring of high-alpine snow dynamics with Cosmic-Ray neutron sensing – a case study at two locations at the Zugspitze Massif

Monitoring snow water resources is crucial to understand the dynamics of snow-fed mountain rivers. Still, in harsh and remote environments like mountain regions using conventional measurement techniques remains particularly challenging. Cosmic-Ray Neutron Sensing (CRNS) constitutes an emerging method for autonomous and non-invasive monitoring of soil moisture and snow dynamics at intermediate spatial scales of several hectares. The method is therefore promising for monitoring snow water equivalent (SWE) in high alpine locations.

The analysis includes two sites at the Zugspitze Massif, differing in elevation and surrounding topographical features. Both sensors have been installed inside existing buildings with steep roofs to avoid snow accumulation, rather than establishing new infrastructure in complex terrain. The CRNS at the Environmental Research Station Schneefernerhaus (UFS, 2656 m a.s.l.) was installed in November 2015 in the Kugelalm located on one of the terraces. A second CRNS was installed in October 2023 in the building of “Zugspitze Geodynamic Observatory Germany” (ZUGOG) operated by the German Research Centre for Geosciences (GFZ) at the summit (2962 m a.s.l.). The CRNS signal is compared against spatially distributed reference SWE based on manual measurements, terrestrial lidar and airborne photogrammetry. Furthermore, Monte Carlo based neutron simulations using the URANOS model and a dedicated modular scenario tool (YULIA) are performed to characterize the local dynamics at the measurement sites.

First results prove that CRNS is suitable for monitoring SWE dynamics even at high alpine locations like the Zugspitze Massif. At UFS the neutron counts reveal both extremely dry years, like 2022, but also very snow-rich years, like 2019 and 2024, which were among the wettest since 2015. The high altitude, the shape of the steep topography and the rocky underground with limited soil cover reduce the statistical error and increase the seasonal dynamics in the neutron flux, facilitating CRNS based SWE monitoring. Another noteworthy aspect is, that due to the large measurement footprint of several hectares, CRNS can even be used when installed within existing buildings, thus reducing costs and limiting the environmental impact of the installation.