地況の地表面日射量および地温に与える影響について

Abstract

It was clear that the ground condition had a large effect on the underground temperatureat 1 m depth. Then, the effect was divided into external factor and internal factor and eachfactor was discussed on the basis of the data obtained in the Matsunoyama landslide area in NiigataPrefecture in summer and in the Miyagami landslide area in Hyogo Prefecture in spring 1974. As aresult of the discussion, the followings were obtained.There were large differences between shelter ratios of solar radiation of several grounds ofdifferent surface conditions as external factor. It was largest on forest (82%), 60% on grassfield, 38% on rice field and smallest on blad land (0%). Therefore, the ground surface of blad landcould receive the largest heat quantity.On the other hand, as internal factor, the differences of heat character and soil compositionin shallow layer were discussed in each ground. The heat quantity that was necessary for risingthe temperature of soil column in the invariable layer by 1°C was 25.5 cal cm-2 deg-1 in the baldland, 27.0 cal cm-2 deg-1 in the grass field, 18.9 cal cm-2 deg-1 in the rice field and 12.9 cal cm-2deg-1 in the forest. Therefore, the heat quantity was smallest in the forest.Adding up the two factors, the soil column in the forest showed the highest temperature incase of the same heat quantity, but the soil column in the blad land showed the highest temperatureand in the forest showed the lowest temperature, considering the shelter ratios in each ground.Accordingly in summer season, the effect of ground condition on ground temperature was determinedmainly by the shelter ratios of solar radiation. As the heat quantity reaching to the ground surfacewas largest in the blad land and smallest in the forest, the heat quantity per day stored in the soilcolumn at each ground was largest in the blad land and smallest in the forest.As mentioned above, it was deduced that the difference of heat quantity stored at every daycaused that of temperature amounting to ±2°C at 1 m depth between each ground.