Evaluation of surface variations in solar radiation income over complex terrains

Using the elevation data, which was offered by the National Land Numerical Information with a 250-m grid size, an estimation model was proposed for the evaluation of radiation conditions as a potential income of solar energy. The model is available for the agro-meteorological investigations over mountainous regions. The main subjects of the present study are verifications of the proposed model, and clarifications of the influence of solar radiation income on the agricultural environment and on the location of agricultural land use. The results were summarized as follows: 1) Especially at the surface of complex terrain, the surrounding configurations have a remarkable affect on their own shadows. Consequently, it is necessary for the present model to take into account the distribution of configurations located in the area with a radius of 10-km. 2) The shadows made by surrounding configuration leads reductions not only in the sunshine duration but in the amount of the solar radiation. The extents of the shadow on reference areas, are closely connected with the spatiality of configurations and the elevation of the sun. 3) The solar radiation flux on a unit (250-m grid) area of natural surfaces changes with the seasons, the angle of the inclination and the direction of the original surface. The slopes toward the south get the direct solar radiation flux efficiently throughout the year. 4) For a rational evaluation of the radiation condition over complex terrains, the grid size of base maps must be reduced to 250-m in space under the conditions of a low sun elevation and at around the winter solstice. The estimation by the grid size of 250-m feasibly represents the thermal conditions over complex terrains. Using the present model, it is able to show a reasonable arrangement of the locations for farms