Snowfall interception in Arizona ponderosa pine forests.

The behavior of intercepted snow on a stand of uneven-aged ponderosa pine in east-central Arizona was evaluated, with the use of a super 8-mm time-lapse movie camera, to determine the relative significance of snowfall interception in the water yield of this type forest. A snow load index was developed to estimate interception storage for two trees in the field of view for discrete time periods. The snow load index, photographs, and climatic data were combined to evaluate accumulation and to identify and rank according to relative magnitudes the basic processes of canopy snow removal. The rate of snow accumulation, which was nonlinear, appeared to be a function of climatic conditions, the rate of incoming precipitation, and the density of crown foilage. Snowslide appeared to be the dominant process of canopy snow removal during the study period, with melt, wind erosion, evaporation of meltwater, and sublimation of canopy snow occurring in order of decreasing significance. Most of the intercepted snow reached the snowpack on the ground, representing no significant loss to the water budget on site. Some water apparently was lost because of evaporation and sublimation but these losses appeared to be comparatively minor.