Evaluation method for evapotranspiration with soil moisture changes and applications to the south-western slope of Mt. Merapi

抄録

The evaluation method for evapotranspiration and its application to the actual area of pyroclastic deposit on the south-western slope of Mt. Merapi volcano are presented in this paper. In the study sites (Gunung Maron site at an altitude of 960m and Pusung Malang that of 1200m), it can be assumed that the amount of evapotranspiration can be evaluated by two processes. One depends on the transpiration by plants which is related to the water absorbed from the soil through their roots, the other is due to direct evaporation from the ground surface. We can evaluate the water balance for a soil layer by adding; the amount of water which infiltrates from the ground surface during rainfall, gravitational water moving down and passing through the layer, evaporation water through the ground surface and transpiration water by plant leaves. On the basis of this idea, an unsaturated water flow simulation is carried out to evaluate the amount of evapotranspiration by using soil suctions observed at two sites. The results show that the annual amount of evapotranspiration from August 1992 to July 1993 is about 1600mm at Gunung Maron, and the seasonal amount from August to November 1992 is about 500mm at Pusung Malang.