The Mogami River basin enclosed by high mountains of Asahi, Iide and Ohu, has snow melt runoffs which begin at the middle of March and last about two months. The total outflow of the runoffs occupies about 40% of the annual outflow, becoming a major resource of the water supply. The runoff also transports huge amount of various materials suspended or solved in the water. Illuminating the suspended substance in the runoff, this study analyses the temporal and spatial characteristics of the concentration and the total flux of the transport. The observation was performed on May 2, 1996 by using hand made samplers specially designed for the high speed flow, covering the confluence of five major branches. NOAA AVHRR data, and time sequential data of the discharge and turbidity have been collected to examine the snow covered area, and temporal characteristic, respectively. Spatial distributions of concentration and sediment transport indicate that the catchment of Nagasaki, which includes Iide and Asahi mountains having wide snow covered area, yields dominant amount of the wash load. Time sequences of the concentration and discharge at Shimono result in the suspended substance transport integrated in April and May 1996 of about 1.5E8kg. It is shown that the concentration is proportional to 1.44 power of the discharge, but the coefficient of proportionality decreases for the later runoff. This phenomena may be interpreted that the decrease of wash load material in the basin by washout influences the concentration. This mechanism is modeled to reproduce the concentration by using only the time history of the discharge.

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Land surface parameterizations (LSPs) are embedded in atmospheric numerical models and express the exchange of water and energy at the land surface. Under Global Soil Wetness Project (GSWP), the water balances in 1987 and 1988 were estimated by a few LSPs with common forcing data, such as precipitation and radiation. The estimates were validated by discharge data using the global river channel network, which was named Total Runoff Integrating Pathways (TRIP). As a result, the LSPs were found to calculate annual water balance fairly well where the forcing precipitation was estimated from enough density of raingauge observations (≥30/10(SUP)6(/SUP)km(SUP)2(/SUP)).

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This paper analyzes the dynamic nature of the near stream flow mechanism in a forested mountain catchment, showing the flow mechanism changing with the antecedent conditions, magnitude and intensity of the rain. The transient nature of the near stream flow mechanism is demonstrated with stream bank tensiometer data. The stream SC (Specific Electric Conductance) behavior is explained by the different flow paths taken during different moisture content stages in the soil. The mobilization of near stream vadose zone water due to rain water input and possible later effect of blending of upslope water with near stream water are demonstrated. The direct correlation between pre-event base flow and after event baseflow SC values is shown and the relevant flow mechanism identified. Baseflow is shown to have a lower SC signal contrary to the normally expected high values. This result is verified in a laboratory soil column test. Physical and chemical data are presented to suggest the baseflow generation mechanism to be an unsaturated matrix flow along the clayey layer and the occasional upslope inputs to hydrographs to be saturated matrix flow along the semi impermeable boundary, once the water reaches that layer. The results of field investigations and soil column experiments show the feasibility of flow path determination by the chemical fingerprint on the stream and soil water samples.

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Several methods for estimating daily potential evaporation (Ep) and daily actual evaporation (Ea) were tested with observations on a bare field. The methods used for estimating Ep were the method to solve the surface heat balance (X-method), the Makkink method, the method to multiply the equilibrium evaporation under strong winds by the empirical constant (Y-method), the Penman method and the Priestley-Taylor method. Among them, the Makkink method, which required only the solar radiation and air temperature, offered the best results for estimating Ep. The methods used for estimating Ea were three methods which multiply the estimates of Ep [using the X-method, the Makkink method, or the Y-method] by the evaporation ratio and the method to solve the surface heat balance with the soil resistance. Both the evaporation ratio and the soil resistance were expressed as functions of the volumetric soil moisture content within the top 2cm layer, which was measured at 9 a.m.. Among them, the last method offered the best results for estimating Ea, and the method to multiply the estimates of Ep using the Makkink method by the evaporation ratio was graded next.

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Potential evaporation and wetness index were estimated at 66 meteorological stations in Japan. The annual amount of potential evaporation is 700-900mm in northern Japan and 1, 000-1, 200mm in southern Japan. The wetness index (WI), which is a ratio of the annual precipitation (P) to the annual potential evaporation (EP), is estimated at 1 to 2. As an application of normalization by the potential evaporation, the definite relation was found between the normalized forest evapotranspiration (E/EP) and the wetness index (WI=P/EP). For a humid climate, i.e. in a region of WI>1, it was shown that E/EP ranges from 0.8 to 0.9.

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Potential evaporation and wetness index over China were estimated by the use of routine meteorological data. The annual amount of potential evaporation is 1, 400 to 1, 600mm over the western part of the Tibetan Plateau and the desert regions. A small value of potential evaporation, which ranges from 800 to 1, 000mm, is shown over the eastern part of the Tibetan Plateau and the middle reaches of the Yangtze River. The wetness index (WI), which is a ratio of the annual precipitation to the annual potential evaporation, ranges from 0.01 to 0.1 over the desert regions and from 1 to 2 over the southern China.

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The distribution of acid buffering patterns in the infiltration process was investigated in the soil layers of a temperate forested catchment focusing on their spatial variations. The investigation consisted of catchment-scale hydrochemical observations and in-situ lysimeter experiments done on the surface layer of soil. The spatial variation of the ion components of soil water, and groundwater, observed for each hydrological elementary process in the measured catchment, showed the existence of two spatially different types of acid buffering mechanisms distributed in the infiltration processes. In the top soil layer, which is affected by the nutrient cycle between plants and soil, the buffering was characterized by the reaction of the biologically supplied protons with organic acid and NO3-, in addition to the input by throughfall, being exchanged by Ca2+ and Mg2+ at cation exchange sites. In the lower layer, it was clarified that a dominant role is played by the buffering mechanism where by protons, produced mainly by dissolution and dissociation of soil CO2 gas, are consumed in the process of chemical weathering. It is emphasized that the lower soil layer plays as an important role in evaluating the buffering potential of the scale of catchment.

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Water quality was studied on the rice grown paddy field areas in Ishikari River basin of Hokkaido, Japan, with special concern to irrigation and drainage management. Irrigation water of the study sites show relatively good condition due to less effect of human pollution. Concentration and load of nitrogen(N) and phosphorus(P) are generally higher in drainage water than in irrigation water. Water quality of drainage water tend to fluctuate in wide range, with N and P in various form. Apparent discharge of N and P just after fertilizing were captured. During later period of rice growth, the accumulated N and P in form of organism in soil and water of paddy field, changes its form into inorganic matter, and discharges to the river. As discharge of N and P from rice paddy is restricted in particular period, thus, not only about the control of loss of fertilizer component, but about timing of fertilizing and way of water management will be also necessary for less load discharge.

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