Modeling quasi-three-dimension distribution of solar irradiance on complex terrain

Solar radiation, driving land-atmosphere interactions and terrestrial carbon assimilation, varies both temporally and spatially due to surface gradient, slope aspect and vegetation shading. Here we present a double-shading transposition model (DST) for simulating temporal and spatial distribution of downwelling shortwave solar radiation. The DST model considers influences of both topographic and canopy structure on radiation transmission. It simulates sub-hourly radiation distribution on and beneath vegetation canopy for any weather conditions. The model is tested against observations at two opposite-facing slopes. The simulated above-canopy radiation compares well with the observed data. The simulated under-canopy daily insolation highly correlates with observed net radiation with an R-squared of 0.90 and 0.91, at the two slopes, respectively. The model provides a convenient and effective tool for simulating spatial and temporal variation of solar radiation on mountainous areas with vegetation cover and has great potential in ecohydrological modelling and catchment management.