Assessment of GNSS-based snow water equivalent derivation for operational use under different snowpack conditions

Abstract:

The water stored in the snowpack is a crucial contribution to the hydrological cycle in mountain areas. However, direct measurements of snow water equivalent (SWE) are often scarce, not easy to install and maintain, mostly non-continuous or rather expensive. SWE can be measured non-destructively with low-cost Global Navigation Satellite System (GNSS) sensors as recent studies demonstrated. Besides information on time delay and strength attenuation of GNSS signals through a snowpack, the GNSS-SWE algorithm includes permittivity models for dry and wet snow and derives additionally liquid water content (LWC) and snow height (HS) based on snow density models. Snow density and LWC can vary considerably, e.g. depending on rain-on-snow events, sun exposition and elevation. Therefore and for assessing the applicability of the GNSS-SWE measurements for operational applications, we operated four GNSS stations along a steep elevation gradient (820, 1185, 1510, and 2540 m a.s.l.) in the Eastern Swiss Alps during two winter seasons (2018-2020). The GNSS-derived SWE estimates agreed very well with manual reference measurements along the elevation gradient, although significant differences in snow density and meteorological conditions existed between the locations. The GNSS-derived SWE accuracy was better than for other automatic SWE sensors. The accuracy was similar under wet- and dry-snow conditions (RMSRE = 12 %). However, GNSS was found to be less suitable for determining daily solid precipitation (water equivalent of new snow) compared to manual measurements or pluviometer recordings. The additionally GNSS-derived HS correlated well with the validation data. The GNSS-derived LWC reliably indicated the onset of snow melt. We conclude that SWE can be reliably determined operationally using low-cost GNSS-sensors under a broad range of climatic conditions.