Forest Canopy Density Effects on Snowpack Across the Climate Gradients of the Western United States Mountain Ranges

Controlled field experiments to disentangle the effect of canopy density from the effect of climate on snowpack dynamics are limited by the underlying linkage between canopy density and climate. Thus, based on observations alone, it is not well understood how variations in canopy density can affect snow processes under different climate regimes. To address this knowledge gap, this study uses a physics-based modeling approach to evaluate the sensitivity of snowpack dynamics to variations in canopy density across the climate gradients of the Western U.S. as represented by 228 Snow Telemetry (SNOTEL) sites. Within the model, we uniformly parameterize the canopy across sites to represent an idealized forest with high, medium, and low canopy density, respectively. The results illustrate that the effect of canopy density on the peak snow water equivalent (SWE) and duration of under-canopy snowpack is sensitive to winter climate (i.e., climatological winter precipitation and temperature). As canopy density decreases, the greatest increase in peak SWE and snowpack duration is found in wet/warm and dry/cold climates, where snowpack under low-density forest lasts longer than that in the open. In comparison, peak SWE and snowpack duration in wet/cold climates are less sensitive to changing canopy density. Thus, forest management actions (e.g., thinning and clearing) are likely to have disparate impacts on snow depending on local winter climate. Climate sensitivity of under-canopy snowpack suggests that snowpack duration under dense canopy in presently warm winter climates is expected to experience the greatest reduction under a warming climate.

Automated summary

This study uses a physics-based modeling approach to evaluate the sensitivity of snowpack dynamics to variations in canopy density across different climate regimes in the Western U.S. It shows that the effect of canopy density on snowpack dynamics is influenced by winter climate, with the greatest impact observed in wet/warm and dry/cold climates. The results suggest that forest management actions may have different effects on snowpack depending on local winter climate.