Measurements from two forested catchments in the mixed conifer, Red Fir zone of the southern Sierra Nevada (2,200-2,600 m elevation) demonstrate the controls that topography and canopy cover exert over snow cover. Snow-depth, soil-moisture, stream-stage and sap-flow measurements from the Wolverton basin in Sequoia National Park and Teakettle Experimental Area in the Sierra National Forest exhibit distinct and rapid responses to spring snowmelt. Spatial heterogeneity in snow water equivalent is influenced by tree clusters and individual canopies. Snowmelt and soil moisture timing are controlled by proximity to stem of tree and canopy clustering. Aspect and slope position affect soil moisture, with drier conditions predominating on the steeper slopes. Synchronous fluctuations in soil moisture, stream flow and sap flow were observed. Continuous instrumental and synoptic survey data show snow water equivalent is approximately 15% less 1 m from the tree stem than in open areas at peak accumulation, with snowmelt occurring in shaded open areas 1 to 4 weeks later than under canopy. Soil moisture tracks the snowmelt pattern closely, with diel fluctuations in soil moisture under saturated conditions followed by an exponential dry-down to field capacity after snowmelt. This is followed by a prolonged summer drought punctuated by rain events of <5% of total precipitation. Synoptic surveys of steeper slopes and multiple aspects show consistent patterns of drier conditions on steeper terrain.
Kirchner, P., Bales, R., North, M., Small, E. (2008): Snowmelt infiltration and evapotranspiration in Red Fir forest ecosystems of the Sierra Nevada. Fall meeting, American Geophysical Union, December 2008. 89(53). Abstract C21C-0572..