Rainwater propagation through snowpack during rain-on-snow sprinkling experiments under different snow conditions

The seasonal snowmelt period is a critical component of the hydrologic cycle for many mountainous areas. Changes in the timing and rate of snowmelt as a result of physical hydrologic flow paths, such as longitudinal intra‐snowpack flow paths, can have strong implications on the partitioning of meltwater amongst streamflow, groundwater recharge, and soil moisture storage. However, intra‐snowpack flow paths are highly spatially and temporally variable and thus difficult to observe. This study utilizes new methods to non‐destructively observe spatio‐temporal changes in the liquid water content of snow in combination with plot experiments to address the research question: What is the scale of influence that intra‐snowpack flow paths have on the downslope movement of liquid water during snowmelt across an elevational gradient? This research took place in northern Colorado with study plots spanning from the rain‐snow transition zone up to the high alpine. Results indicate an increasing scale of influence from intra‐snowpack flow paths with elevation, showing higher hillslope connectivity producing larger intra‐snowpack contributing areas for meltwater accumulation, quantified as the upslope contributing area required to produce observed changes in liquid water content from melt rate estimates. The total effective intra‐snowpack contributing area of accumulating liquid water was found to be 17, 6, and 0 m2 for the above tree line, near tree line, and below tree line plots, respectively. Dye tracer experiments show capillary and permeability barriers result in increased number and thickness of intra‐snowpack flow paths at higher elevations. We additionally utilized aerial photogrammetry in combination with ground penetrating radar surveys to investigate the role of this hydrologic process at the small watershed scale. Results here indicate that intra‐snowpack flow paths have influence beyond the plot scale, impacting the storage and transmission of liquid water within the snowpack at the small watershed scale.

Section: Discussionmentioning

confidence: 99%

Hydrologic connectivity at the hillslope scale through intra‐snowpack flow paths during snowmelt

Webb

Wigmore

Jennings

et al. 2020

“…Additionally, within the snowpack, certain processes remain difficult to assess. Würzer et al (2017) and Juras, Würzer, Pavlásek, Vitvar, and Jonas (2017) showed that preferential vertical flow of liquid water within a snowpack considerably influences rain water retention. Eiriksson et al (2013) further revealed the importance of preferential lateral flow in sloped terrain for runoff formation in complex topography.…”

Section: Results In the Context Of Hydrological Modellingmentioning

confidence: 99%

Spatio‐temporal aspects of snowpack runoff formation during rain on snow

Würzer¹,

Jonas²

2018

Self Cite

Rain on snow (ROS) is a complex phenomenon leading to repeated flooding in many regions with a seasonal snow cover. The potential to generate floods during ROS depends not only on the magnitude of rainfall but also on the areal extent of the antecedent snow cover and the spatio‐temporal interaction between meteorologic and snowpack properties. The complex interaction of these factors makes it difficult to accurately predict the effect of snow cover on runoff formation for an upcoming ROS event. In this study, the detailed physics‐based snow cover model SNOWPACK was used to assess the influence of snow cover properties on converting rain input to available snowpack runoff during 191 ROS events for 58 catchments in the Swiss Alps. Conditions identified by the simulations that led to excessive snowpack runoff were a large snow‐covered fraction, spatially homogeneous snowpack properties, prolonged rainfall events, and a strong rise in air temperature over the course of the event. These factors entail a higher probability of snowpack runoff occurring synchronously within the catchment, which in turn favours higher overall runoff rates. The findings suggest that during autumn and late spring, flooding due to ROS is more likely to happen, whereas during winter a coincidence of the above conditions in the study area is quite rare. For example, an autumn event which occurred in October 2011 resulted from a combination of spatially homogeneous snowpack conditions following a recent snowfall and high, but not exceptional rainfall, and led to major flooding. The results of this study provide key factors to assess in advance of an incoming ROS event and emphasize the importance of detailed snow monitoring for flood forecasting in snow‐affected watersheds.

“…This was because there was no extreme rain‐on‐snow event which would supply a significant amount of liquid water into the snowpack. However, this heat exchange might be important when assessing the energy balance at daily and shorter temporal resolutions (Juras, Würzer, Pavlasek, Vitvar, & Jonas, 2017; Würzer et al, 2016). In general, rain input might be a significant heat flux for basins with air temperature fluctuating near the freezing point during winter months and thus rain events occur more often.…”

Section: Discussionmentioning

confidence: 99%

The impact of changing subcanopy radiation on snowmelt in a disturbed coniferous forest

Hotovy

Jeníček

2020

Understanding the role of forests on snowmelt processes enables better estimates of snow storages at a catchment scale and contributes to a higher accuracy of spring flood forecasting. A coniferous forest modifies the snowpack energy balance by reducing the total amount of solar shortwave radiation (SWR) and enhancing the role of longwave radiation (LWR) emitted by trees. This study focuses on changes in SWR and LWR at three sites with different canopy structure (Bohemian Forest, Czechia), including one site affected by the bark beetle (Ips typographus). Measurements of incoming and outgoing SWR and LWR were performed at all sites equipped with CNR4 Net Radiometers for three cold seasons. In addition to SWR and LWR, sensible and latent heat, and ground heat and energy supplied by liquid precipitation were calculated. The results showed that net SWR at the healthy forest site represented only 7% of the amount at the open site due to the shading effect of trees. In contrast, net LWR represented a positive component of the snowpack energy balance at the healthy forest site and thus contributed the most to snowmelt. However, the modelled snowmelt rates were significantly lower in the forest than in the open area since the higher LWR in the forest did not compensated for the lower SWR. The progressive decay of disturbed forest caused the decrease in mean net LWR from −3.1 W/ m 2 to −12.9 W/m 2 and the increase in mean net SWR from 31.6 W/m 2 to 96.2 W/ m 2 during the study period. These changes caused an increase in modelled snowmelt rates by 50% in the disturbed forest, compared to the healthy forest site, during the study period. Our findings have important implications for runoff from areas affected by land cover changes due to either human activity or climate change.