Modelling daily topographic solar radiation without site-specific hourly radiation data

This paper proposes a model to estimate absolute values of daily solar radiation intercepted by topographic surface, without site-specific hourly radiation data. Instead, daily amounts of global and diffuse radiation at the horizontal surface under unobstructed sky are used. These amounts can be simply and accurately estimated (as monthly averages) in terms of latitude, elevation, and relevant but easily accessible climatic parameters. Hourly values of direct irradiance are substituted here by the hourly portions of the unknown daily total as a function of actual and daily maximum solar elevation. The presented approach simplifies ecological application of topographic solar radiation models, especially for research of the spatial distribution of vegetation and ecosystem types. (C) 1998 Elsevier Science B.V. All rights reserved.