Preprints
https://doi.org/10.5194/egusphere-2023-3012
https://doi.org/10.5194/egusphere-2023-3012
19 Jan 2024
 | 19 Jan 2024
Status: this preprint is open for discussion.

Impact of rain-on-snow events on snowpack structure and runoff under a boreal canopy

Benjamin Bouchard, Daniel F. Nadeau, Florent Domine, Nander Wever, Adrien Michel, Michael Lehning, and Pierre-Erik Isabelle

Abstract. Rain-on-snow events can cause severe flooding in snow–dominated regions. These are expected to become more frequent in the future as climate change shifts the precipitation from snowfall to rainfall. However, little is known about how winter rainfall interacts with an evergreen canopy and affects the underlying snowpack. In this study, we document 5 years of rain-on-snow events and snowpack observations at two boreal forested sites of eastern Canada. Our observations show that rain-on-snow events over a boreal canopy leads to the formation of melt–freeze layers as rainwater refreezes at the surface of the sub–canopy snowpack. They also generate frozen percolation channels, suggesting that preferential flow is favored in the sub–canopy snowpack during rain-on-snow events. We then used the multi–layer snow model SNOWPACK to simulate the sub–canopy snowpack at both sites. Although SNOWPACK performs reasonably well in reproducing snow height (RMSE = 17.3 cm), snow surface temperature (RMSE = 1.0 °C), and density profiles (agreement score = 0.79), its performance declines when it comes to simulating snowpack stratigraphy, as it fails to reproduce many of the observed melt–freeze layers. To correct for this, we implemented a densification function of the intercepted snow in the canopy module of SNOWPACK. This new feature allows 27 of the 32 observed melt–freeze layers induced by rain-on-snow events to be formed by the model, instead of only 18 with the original canopy module. This new model development also delays and reduces the snowpack runoff. Indeed, it triggers the unloading of dense unloaded snow layers with small rounded grains, which in turn produces fine–over–coarse transitions that limit percolation and favor refreezing. Our results show that the boreal vegetation modulates the sub–canopy snowpack structure and runoff from rain-on-snow events. Overall, this study highlights the need for canopy snow properties measurements to improve hydrological models in forested snow–covered regions.

Benjamin Bouchard, Daniel F. Nadeau, Florent Domine, Nander Wever, Adrien Michel, Michael Lehning, and Pierre-Erik Isabelle

Status: open (until 28 Mar 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Benjamin Bouchard, Daniel F. Nadeau, Florent Domine, Nander Wever, Adrien Michel, Michael Lehning, and Pierre-Erik Isabelle

Data sets

December 11, 2023 (v1) Dataset Open Dataset from "Impact of rain-on-snow events on snowpack structure and runoff under a boreal canopy" Benjamin Bouchard, Daniel F. Nadeau, Florent Fomine, Nander Wever, Adrien Michel, Michael Lehning, and Pierre-Erik Isabelle https://doi.org/10.5281/zenodo.10357450

Model code and software

Documented code of SNOWPACK version 3.6.0 WSL-SLF GitLab repository https://gitlabext.wsl.ch/snow-models/snowpack

Benjamin Bouchard, Daniel F. Nadeau, Florent Domine, Nander Wever, Adrien Michel, Michael Lehning, and Pierre-Erik Isabelle

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Short summary
Observations over several winters at two boreal sites in eastern Canada show that rain-on-snow (ROS) events lead to the formation of melt-freeze layers and that preferential flow is an important water transport mechanism in the subcanopy snowpack. Simulations with SNOWPACK generally show good agreement with observations, except for the reproduction of melt-freeze layers. This was improved by a time-based intercepted snow densification function, which also modulates ROS-induced runoff.