Saturated areas through the lens: 1. Spatio‐temporal variability of surface saturation documented through thermal infrared imagery

Surface saturated areas are key features in generating run‐off. A detailed characterization of the expansion and contraction of surface saturation in riparian zones and its connectivity to the stream is fundamental to improve our understanding of the spatial and temporal variability of streamflow generation processes. In this first contribution of a series of two papers, we used ground‐based thermal infrared imagery for characterizing riparian surface saturation seasonal dynamics of seven different riparian areas in the Weierbach catchment (0.42 km2), a small forested catchment in Luxembourg. We collected biweekly panoramic images of the seven areas over a period of 2 years. We identified the extension of saturation in each collected panoramic image (i.e., percentage of pixels corresponding to saturated surfaces in each riparian area) to generate time series of surface saturation. Riparian surface saturation in all areas was seasonally variable, and its dynamics were in accordance with lower hillslope groundwater level fluctuations. Surface saturation in the different areas related to catchment outlet discharge through power law relationships. Differences in these relationships for different areas could be associated with the location of the areas along the stream network and to a possible influence of local riparian morphology on the development of surface saturation, suggesting a certain degree of intracatchment heterogeneity. This study paves the way for a subsequent investigation of the spatio‐temporal variability of streamflow generation in the catchment, presented in our second contribution. Seasonal dynamics of surface saturation in different riparian areas reflected catchment storage variability and low hillslope's groundwater fluctuations. Differences in the surface saturation versus baseflow discharge relationships for the different riparian areas could be attributed to areas' location along the stream network (i.e., area elevation) and local riparian morphology (i.e., area width).