Abstract. Seasonal snowpack deeply influences the distribution of
meltwater among watercourses and groundwater. During rain-on-snow (ROS)
events, the structure and properties of the different snow and ice layers
dictate the quantity and timing of water flowing out of the snowpack,
increasing the risk of flooding and ice jams. With ongoing climate change, a
better understanding of the processes and internal properties influencing
snowpack outflows is needed to predict the hydrological consequences of
winter melting episodes and increases in the frequency of ROS events. This
study develops a multi-method approach to monitor the key snowpack
properties in a non-mountainous environment in a repeated and
non-destructive way. Snowpack evolution during the winter of 2020–2021 was
evaluated using a drone-based, ground-penetrating radar (GPR) coupled with
photogrammetry surveys conducted at the Ste-Marthe experimental watershed
in Quebec, Canada. Drone-based surveys were performed over a 200 m2
area with a flat and a sloped section. In addition, time domain
reflectometry (TDR) measurements were used to follow water flow through the
snowpack and identify drivers of the changes in snowpack conditions, as
observed in the drone-based surveys. The experimental watershed is equipped with state-of-the-art automatic
weather stations that, together with weekly snow pit measurements over the
ablation period, served as a reference for the multi-method monitoring
approach. Drone surveys conducted on a weekly basis were used to generate
georeferenced snow depth, density, snow water equivalent and bulk liquid
water content maps. Despite some limitations, the results show that the combination of drone-based GPR, photogrammetric surveys and TDR is very promising for assessing
the spatiotemporal evolution of the key hydrological characteristics of the
snowpack. For instance, the tested method allowed for measuring marked
differences in snow pack behaviour between the first and second weeks of the
ablation period. A ROS event that occurred during the first week did not
generate significant changes in snow pack density, liquid water content and
water equivalent, while another one that happened in the second week of
ablation generated changes in all three variables. After the second week of
ablation, differences in density, liquid water
content (LWC) and snow water equivalent (SWE) between the flat and the
sloped sections of the study area were detected by the drone-based GPR
measurements. Comparison between different events was made possible by the
contact-free nature of the drone-based measurements.