Inferring snowpack ripening and melt-out from distributed measurements of near-surface ground temperatures

摘要

Seasonal snow cover and its melt regime are heterogeneous both in time andspace. Describing and modelling this variability is important because itaffects diverse phenomena such as runoff, ground temperatures or slopemovements. This study presents the derivation of melting characteristicsbased on spatial clusters of ground surface temperature (GST) measurements.Results are based on data from Switzerland where ground surface temperatureswere measured with miniature loggers (iButtons) at 40 locations referred toas footprints. At each footprint, up to ten iButtons have been distributedrandomly over an area of 10 m × 10 m, placed a few cm below theground surface. Footprints span elevations of 2100–3300 m a.s.l. and slopeangles of 0–55°, as well as diverse slope expositions and types ofsurface cover and ground material. Based on two years of temperature data,the basal ripening date and the melt-out date are determined for eachiButton, aggregated to the footprint level and further analysed. The melt-outdate could be derived for nearly all iButtons; the ripening date could beextracted for only approximately half of them because its detection based onGST requires ground freezing below the snowpack. The variability within afootprint is often considerable and one to three weeks difference betweenmelting or ripening of the points in one footprint is not uncommon. Thecorrelation of mean annual ground surface temperatures, ripening date andmelt-out date is moderate, suggesting that these metrics are useful for modelevaluation.