Three models of interception process : Rutter model with Deardorff's power function, Deardorff model and Modified Kondo model, each in combination with Penman-Monteith equation applied to the same climatic forcing over the year of simulation were compared. The modification of the Kondo's model done in our study includes the water balance component, between storms evaporation and transpiration including the power function, storage changes and the canopy drainage. The comparison was meant for assessing the simple Modified Kondo model developed in Japan and demonstration of the importance of the power function. The Penman-Monteith equation was the kernel for determination of evaporation and transpiration rates. Its use in this study was proposed because it has been widely used in Japan and in experimental sites and therefore can be used as a basis for comparison. Since much interest was on net rainfall, the control volume for the water accounting was between top of the canopy and above the ground surface and hence does not include soil moisture and transpiration. Results showed that forest canopy evaporation ranged from 22 to 29% of gross rainfall. Much model prediction differences were observed in winter, with lower rainfall intensity where wet canopy storages or rainfall did not meet the potential (atmospheric) evaporation demand. The annual net rainfall and transpiration ranged from 71 to 78% of gross rainfall and from 727 to 733 mm respectively. The adopted power function had significant impact on transpiration rate and small impact on evaporation rate for the Modified Kondo model. The Modified Kondo model predicted fairly close to the two models and therefore can be used for providing hourly input into hydrological models. The differences in the predicted hydrological fluxes resulted from the different model formulations especially throughfall coefficients and drainage functions.

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This paper compares AMS (Annual Maximum Series) method with PDS (Partial Duration Series) method in hydrologic frequency analysis through a Monte Carlo experiment. The numerical experiment takes into account the seasonality inherent in hydrologic processes. Based on 174 two-day areal rainfall series in 43 years and 117 flood peak discharge series in 47 years, statistical analysis has revealed the difference between the actual occurrence process and the Poisson process that holds for rare events. For two series of two-day rainfalls and peak discharges, the Monte Carlo experiment deals with distribution of occurrence interval and distribution of extreme rainfalls and discharges. The exponential distribution for inter event time is used for the Poisson process, while the empirical distributions obtained by the statistical analysis are used for seasonal rainfall and discharge series. The experiment has revealed the importance of the effect of seasonality. When applying the GEV (Generalized Extreme Value) distribution to AMS, one would overestimate 100-year quantile because of ignoring the seasonality. However, if the quantile estimate obtained by the GP (Generalized Pareto) distribution for PDS is almost the same as the one by GEV-AMS approach, the use of GEV can be justified. It was also concluded that the average number of PDS elements in a year should be four or more to avoid the overestimation by the GEV-AMS approach.

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We discussed the changes in baseflow for about twenty years after a forest fire in Etajima Island, Hiroshima Prefecture. We focused on the low flow at a fire-damaged catchment when the daily runoff at a control catchment is less than 1.0mm/d, and analyzed the low flow according to the season and the low flow class. We found that the low flow has decreased for about 20 years after the fire regardless of the season and the low flow class. However, the patterns of the low flow reduction depended on the seasonal precipitation. In usual precipitation condition, the reduction of the low flow was maximum at spring-summer, followed by summer-fall, and winter. Also, the low flow reduced with a decreasing in flow class. In scarce precipitation condition, the reduction at summer-fall increased greatly. At the minimum flow class, the reduction increased remarkably. These results imply that (1) the increase of evapotranspiration with the forest vegetation recovery reduces the low flow, (2) the increase of evapotranspiration brings the soil moisture deficit in winter, (3) the evapotranspiration has little influence on the smaller low flow, and (4) the generation process and flow-path of the low flow is different according to the low flow class.

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To avoid CO2 degassing and the following pH increase in soil water, pH measurement using the tensionic method was carried out and its performance was discussed. The pH of distilled water stored in a buried-type tensiometer equilibrated with the pH of surrounding soil water more rapid than the concentration of dissolved ions. This was theoretically supported by much greater diffusion coefficient of proton due to its particular diffusion mechanism in solution. The time to reach the equilibrium condition of dissolved ions became longer as the soil was getting drier. The pH of the stored water was lower than that of soil suspension, and higher than that of pure water under the same CO2 concentration. Concentrations of CO2 and dissolved ions suggested that CO2 dissolution and cation exchange reaction affected soil water pH. In conclusion, it is possible to measure the pH of soil water under high CO2 concentrations in soils by applying the tensionic method.

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The observation of surface runoff was carried out on an experimentally ash-covered slope in Unzen volcano. By applying the some simple models to the obtained data, the accuracy of the estimation and the characteristics of the parameters of the models were compared. Here tank-model (Yamakoshi and Suwa, 2000) and Hortonian experimental-equation model (reference from Shiraki, 1997) were used to calculate effective rainfall, and kinematic-wave model and another tank-model were used to determine the shape of hydrograph. There was little difference of the accuracy between the two effective-rainfall models. While the determination of hydrograph, the accuracy of tank-model was slightly better than that of kinematic-wave model, partly because the former had the more number of parameters. Applying the obtained parameters to the rainfall event which contained the maximum rainfall intensity in 10 minutes in the observation period, it was commonly defined the period when the influence of volcanic ashes became small rapidly. As the result of comparing the feature of the parameters of each effective-rainfall models, the parameters of Hortonian equation model were more effective than those of tank-model (Yamakoshi and Suwa, 2000), for consideration of the variation of the infiltration characteristics. In determining hydrograph, each models had its advantage. The parameter of kinematic-wave model held the information of roughness coefficient, while use of tank model had the calculation time much shorter.

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The sum of the heat fluxes observed with the eddy covariance over a larch forest canopy in eastern Siberia is around 80% of the available energy. An analysis on the variation of the canopy conductance suggests that at least the latent heat flux is underestimated. The co-spectra of the fluctuations of temperature and humidity with the vertical wind velocity suggests that the contribution of the relatively large scale eddy (i.e., fluxes in the low frequency range) is evaluated insuffciently. Energy transportation including relatively large scale eddy is considered, and we define the advection flux as the product of the energy difference between incoming and outgoing air and the volume of advection air. We compute the flux assuming that the incoming air is above forest canopy and that the outgoing air is located at trunk space. The result shows that the advection volume is larger in the unstable condition than in stable atmospheric condition. Mean volume of the advection is 0.06m3m-2s-1. Mean diurnal change in the evaluated advection fluxes are positive in daytime and negative at night for the sensible heat, and always positive for the latent heat. Contribution of the advection flux to the sensible heat flux is 11%, and that to the latent heat flux is 54%. Finally, the total evapotranspiration during growing season is evaluated as 233mm. Thus the soil water extraction from the active layer is implied.

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