Abstract
An ET submodel was developed as a component of long term runoff analysis in the last report. In this report, decision of parameter values of the DS (degree of saturation)-ETR (evapotranspiration ratio) characteristic curves and saturated conductivity in the ET submodel according to every soil texture and land use conditions was tried. First, parameter values concerned with water movement in the soil was decided with a scaling of soils. Second, degree of saturation and evapotranspiration ratio were calculated with SPAC (Soil-Plant-Atmosphere Continuum) model using the parameter values decided with the scaling of soils. Next, the parameter values of DS-ETR characteristic curves were calculated from the calculation results using SPAC model. Finally, calculation of evapotranspiration in a watershed having dry season was done with ET submodel using parameter values obtained above.
As a result, mutual relation of the three parameters of ET submodel is represented by regression equation connecting with soil texture conditions. When the ET submodel is used in calculation of evapotranspiration of a watershed, first, saturated conductivity used in ET submodel is decided, next, parameters of DS-ETR characteristic curves are decided using regression equation obtained above. In the application of ET submodel, it is confirmed that water balance is grasped with ET submodel using proper value of saturated conductivity of a watershed. And it is confirmed that change of evapotranspiration according to soil moisture is able to be represented using ET submodel in long term runoff analysis.
