Net radiation in a snow-covered discontinuous forest gap for a range of gap sizes and topographic configurations

Estimating net radiation on the forest floor is crucial for predicting snowmelt recharge and for quantifying water yield from snow-dominated forested watersheds. However, complex characteristics of radiation transfer in discontinuous forest gaps make this estimation challenging. This study quantifies net radiation within a forest gap for a range of gap sizes, slopes and aspects, and meteorological conditions. The spatial distribution of net radiation in the gap is found to be heterogeneous with southern and northern areas of the gap receiving minimum and maximum energy amounts, respectively. At a midlatitude site and for completely clear sky conditions in the snow season, results suggest that net radiation in the forest gap is minimum for gaps of size equal to half of the surrounding tree height. In contrast, when sky cloudiness in the snow season is considered, net radiation shows a monotonically increasing trend with gap size. Slope and aspect of forest gap floor also impact the net radiation and its variation with gap size. Net radiation is largest and smallest on steep south-facing and north-facing slopes, respectively. Variation of net radiation with slope and aspect is largest for larger gaps. Results also suggest that net radiation in north-facing forest gaps is larger than in open areas for a longer duration in the snow season than in forest gaps on flat and south-facing slopes. Since net radiation directly affects melt recharge and evaporation, these findings have implications on forest and water management, wildfire hazard, and forest health.