Comparison of different automatic methods for estimating snow water equivalent

Manual measurements of snow water equivalent (SWE) require a considerable effort, which is why several automatic methods for single-point SWE estimates have been developed. This study provides a first comprehensive review and comparison of seven different automatic ways to determine SWE and/or the daily new snow water equivalent (HNW). We therefore deployed the methods tested over 4 subsequent winter seasons at a test site in the Swiss Alps. As reference we manually measured SWE on a biweekly schedule and HNW on a daily schedule over the same four winter periods. We tested 4 functional categories of methods: (1) direct recording of SWE (SNOWPILLOW, SNOWPOWER), (2) direct recording of HNW (PARSIVEL, GAUGE), (3) complex numerical models driven by meteorological data (SNOWPACK, COSMO-7), and (4) a simple stochastic model based on snow depth (HS) data (SIMPLE). As at our site melting/sublimation was insignificant for the mass balance during the snow accumulation period, differential SWE data could be converted into HNW, while HNW data could be cumulated to SWE. In general, our assessment showed that most of the methods performed reasonably well with respect to SWE estimations, but featured clear deficiencies with respect to HNW estimations. SNOWPILLOW, SNOWPACK, and SIMPLE showed a reasonable performance with respect to both, SWE and HNW estimates, and may hence be attractive for general-purpose applications. However, method-specific limitations have to be considered. This study is intended to facilitate finding the optimum instrumentation for specific applications, different purposes, and given boundary conditions.