Hiromu Yoshida

Studies and evaluations on interception processes during rainfall based on a tank model

Abstract Some analyses are carried out with regard to canopy interception processes during rainfall events based on a tank model. A hypothesis, rainfall interception rate is proportional to the product of potential evaporation and rainfall intensity, is formed from past experimental data, and is applied to the data in this study. Computational equations are proposed to the interception rate and accumulative interception loss under constant rainfall intensity. Data from the Shirakawatani experimental forested catchment are used in order to examine the relationship between the interception rate and rainfall intensity, the ratio of the interception rate to rainfall intensity and potential evaporation, accumulative interception loss and the rainfall duration, and accumulative interception loss and accumulative rainfall. These regression relations show that interception processes are described by rainfall intensity and potential evaporation. An equation relating the aerodynamic resistance in the Penman–Monteith equation to rainfall intensity is proposed to explain the fact that the interception rate exceeds net radiation.

Modeling energy and water cycle in a forested headwater basin

Abstract A physical-mathematical model is proposed to describe hourly dynamics of water and heat transfers in a forested watershed which is conceptually divided into seven sub-compartments. Hourly, daily and annual water yield, evapotranspiration loss and canopy-soil temperatures are simulated. Inter-connecting energy budget and water balance processes are integrated by simultaneously solving related equations with a specific feedback-iteration method. Emphasis is placed on interaction of transpiration and soil water status, on nonlinear and nonuniform overland flow, and on the controlling function of each storage on water fluxes. The model is calibrated by using the SIMPLEX optimization, at the Shirakawatani catchment in Western Japan, with hydrometeorology data for 2 years. Simulated annual water yield deviated from the observations by only 1.65%, hourly, or daily runoff was statistically correlated to observed runoff at a level of 0.916 or 0.976, and flood process, leaf and soil temperature patterns were fitted well.

MEASUREMENT OF TREE TRANSPIRATION USING LARGE WEIGHING LYSIMETERS

The difference of transpiration process between coniferous and broad-leaved trees is one of the most interesting topics in forest hydrology and other study fields. Direct measurement of transpiration is indispensable for detailed discussion on the topics. The lysimeter is the most effective way to directly measure tree transpiration. In this study, large weighing lysimeters were constructed. Zelkova serrata (Japanese zelkova) and cryptomeria japonica (Japanese cedar) were planted in containers of the lisimeters, and transpiration was measured. The relationship between transpiration and heat pulse velocity which is an reliable index of transpiration rate and actual transpiration rate was investigated. Apparent differences of transpiration rate and process could not be found between two species as far as the results of the measurements.

EVALUATION OF FUTURE CHANGES OF PRECIPITATION, EVAPOTRANSPIRATION AND RUNOFF DISCHARGE DUE TO GLOBAL WARMING

The global warming phenomenon has become of major interest in recent years. The objective of this study is to evaluate the effects of the global warming on precipitation, evapotranspiration, and runoff discharge in two different regions with and without much snow and snowmelt in winter and spring. Two types of future temperature scenarios: Time series scenario and 1°C increase scenario, are employed for predicting the future changes of monthly mean temperature. The occurrance number, duration, and daily rainfall amount of one storm cluster in each month for two warming scenarios are evaluated by the nonstaionary time-series model of rainfall characteristics (Nagura and Hashino, 1996). Future monthly evapotranspiration is estimated as the sum of transpitration and rainfall interception loss. Monthly mean runoff discharge is estimated by the stochastic response model of daily runoff (Yue and Hashino, 1996)

The Runoff Analysis of Total Nitrogen and Phosphorus in a Storm Event in a Forested Basin Using a Tank Model

This study focused on the runoff characteristic of total nitrogen and phosphorusduring a storm event in a forested basin. The stream water was separated into four runoff components using a tank model, and the correlation between those components and the temporal changes of stream water concentration of total nitrogen and phosphorus was investigated. It is clarified that stream water concentration of total nitrogen and phosphorus are formed by the temporal change of runoff components. Then, the modeling of runoff of total nitrogen and phosphorus from a forested basin is employed using a tank model.

Assesment on Development of Golf Links in terms of Headwater Conservation Function

This study investigates the assesment on the development of golf links in terms of the headwater conservation function. Mathematical runoff model developed by authors are applied to a virtual basin based upon Shirakawadani experimental basin in Tokushima prefecture, and simulates the change of daily runoff discharge in various conditions concerned with the infiltration and water retention capacities. The reduction of the capacities by the development of golf links cause the accelerative decrease of daily runoff discharge.

Fundamental Study on Incipient Motion of Coarse Particles in Mixed-Sediment Beds

The threshold condition of the incipient motion of coarse materials in mixed-sediment beds is studied with respect to spherical particles.First, the influence of protrusion and relative depth on the fluid force is clarified experimentally.Secondly, a general equation for the threshold shear velocity is deduced throughthe theoretical consideration of the escape of the coarse particle from a hollowconsisting of the finer sediment. The equation explains very well the experimental results of the threshold condition of isolated spheres.

Investigation of Rainfall Interception Models by Forest Steelow Data

For rainfall interception process in forests, four types of tank models are examined using field observations of gross rainfall, throughfall, and stemflow of a Sugi stand in forests. The models are single tank models and double tank models with different constants and coefficients during a rainfall event from those after the cessation of the rainfall. Parameters in the models are identified by minimizing the square sum of residuals of stemflows. The double tank models obtain better results.