Seasonal Asynchronicity of Wetness and Streamflow in an Alpine Catchment

Soil moisture is a crucial indicator of the seasonal dynamics of storage and fluxes, as the key interface between the surface and atmosphere and the surface and subsurface. At the same time it is the primary ecohydrological water source. In an alpine environment, its seasonal fluctuations are largely governed by radiation via snow melt, evaporation, and transpiration in addition to precipitation arrival, storage, and runoff.  Because of this interaction of fluxes, it offers a critical lens with which to examine catchment processes. Meanwhile, it is one of the most challenging water stores to monitor at relevant scales.

In the Vallon de Nant, a 13.5 km² catchment in Switzerland, over 7 years of in situ data (with intermittent gaps), we observe two distinct peaks, the first in March and the second in December, punctuated by two periods of low soil moisture, in mid-January and over the growing season from June to September.   This is particularly surprising because the stream flow peak does not occur until 3 months later in June.  This time lag has been observed in other alpine catchments and may primarily be an expression of the interplay of wetting and drying, however we might also be observing an artifact of the scale discrepancy between the point measurements of soil moisture and the catchment response of streamflow.  This scale discrepancy can be framed as a threshold-connectivity problem demonstrating the functional roles of hillslope versus riparian catchment areas and their expansion and contraction according to seasonal vegetation activity. 

In this presentation, we will examine the seasonal dynamics of wetting and drying to highlight the compounding roles of topography, season and vegetation.   We will further explore the implications for plant available water given anticipated changes in seasonal snow pack timing and duration.