Snowpack accumulation in forested watersheds depends on the amount of; snow intercepted in the canopy and its partitioning into sublimation,; unloading, and melt. A lack of canopy snow measurements limits our; ability to evaluate models that simulate canopy processes and predict; snowpack and water supply. Here, we tested whether monitoring changes in; wind-induced tree sway can enable snow interception detection and; estimation of canopy snow water equivalent (SWE). We monitored hourly; tree sway across six years based on 12 Hz accelerometer observations on; two subalpine conifer trees in Colorado. We developed an approach to; distinguish changes in sway frequency due to thermal effects on tree; rigidity versus intercepted snow mass. Over 60% of days with canopy; snow had a sway signal in the range of possible thermal effects.; However, when tree sway decreased outside the range of thermal effects,; canopy snow was present 93-95% of the time, as confirmed with; classifications of PhenoCam imagery. Using sway tests, we converted; significant changes in sway to canopy SWE, which was correlated with; total snowstorm amounts from a nearby SNOTEL site (Spearman r=0.72 to; 0.80, p<0.001). Greater canopy SWE was associated with storm; temperatures between -7 C and 0 C and wind speeds less than 4 m/s. Lower; canopy SWE prevailed in storms with lower temperatures and higher wind; speeds. We conclude that monitoring tree sway is a viable approach for; quantifying canopy SWE, but challenges remain in converting changes in; sway to mass and further distinguishing thermal and mass effects on tree; sway.
