The main objective of this study is to establish rainfall-runoff characteristics in wetland, using tank model for different landuse. The area research is Bekanbeushi Wetland Basin located in East-Hokkaido. For determining the parameters of the model, we took stream flow observations at eight locations with different landuse in entire basin. Using this model, verified by comparing with actual measured values, not only the rainfall runoff characteristics of pastures and forests, which were already-known, but also the rainfall runoff characteristics of wetland could be estimated with good accuracy. For watershed containing wetland, we revised the wetland tank model by accounting for the depth of the water in the model. The model was also extended for accounting if the river is surrounded by wetlands by means of incorporating overflow from the river to surrounding wetland areas.

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Ice breakup dates at Saroma-ko lagoon were estimated using water temperature trend by in-situ data and MODIS data. The estimation at Saroma-ko was the test study of estimating ice breakup dates of the lakes on the Eurasian continent by satellite data.
At first, water temperature trend was evaluated by a quadratic or a linear regression using in-situ water temperature data at Saroma-ko. The accuracy of dates when water temperature was 0.0°C estimated by regressions were about 1 or 2 days. Ice breakup dates at Saroma-ko were estimated using these regressions of water temperature. The results showed that the estimation errors were about 2 days after removal of the offset value. Secondly, ice breakup dates at Saroma-ko from 2000 to 2002 were estimated using water temperature trend by MODIS data. The results showed that the difference between estimation and observation was −14 days, and standard deviation was about 4 days. Lastly, the relationships between the frequency of data acquisition, the errors of water temperature, and the accuracy of estimated ice breakup dates were evaluated by the simulation. It revealed that the ice breakup dates were estimated about the 4 days accuracy at Saroma-ko.

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To examine the effects of the bedrock fissures and bedrock subsurface flow on runoff generation mechanisms, a large-size sprinkling experiment was conducted and the numerical analysis was developed. The experimental slope with 6.25m long, 1.5m wide and 30 degrees has three fissures with openings of 2.5cm × 17cm in the middle part of the slope. The 80cm × 110cm × 80cm storage tank was installed under the experimental flume, which was connected from the experimental flume through simulated “fissures”. The infiltrated water and tank water outflow was monitored. The finite element analysis was developed to simulate the bedrock recharge and outflow. The lag time between rainfall peaks to runoff peaks were found to be longer in the case of no tank infiltration than the experimental cases with infiltration to the tank, in which the runoff from the soil coincides with rainfall peak, but the runoff peak from the tank was delayed to the rainfall peak. Compared with the numerical analysis and experimental results, infiltration into the bedrock and the runoff from the bedrock would play important roles for the runoff generation mechanisms.

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By analyzing the time series of measurements of soil moisture at a point along with precipitation and potential evaporation using the bucket with a bottom hole (BBH) model, we evaluated water balance terms at the point. The estimates of those terms made at nine points on a 1.5m grid in a small grass-covered area showed their own spatial variations. The results obtained are summarized as follows.
(a) Ranking of the spatial variability of the water balance terms involved in the BBH model was W (soil moisture) < E (evaporation) < Rs (surface runoff) < Gd (gravity drainage).
(b) Clear patterns showing the spatial variation in surface runoff and gravity drainage in a 3×3m patch were obtained, which suggests that subsurface water below the ASSL (30cm thick) has flow systems on spatial scales of a few meters.
(c) The spatial variation patterns of the water balance terms obtained by the parameterization of the BBH model did not necessarily agree with that of soil moisture but showed ones peculiar to the terms. This means that the parameterization takes the effects of other factors than soil moisture such as the micro topographic relief, vegetation cover, soil texture and structure into account appropriately, because such factors should by nature exhibit spatially not random but organized variations.
(d) Daily evaporation estimates made by the BBH model were in good agreement with the measurements taken for reference by the Bowen ratio method, though it was conducted by the expedient of disregarding an insufficiency of fetch and neglecting the heat flux into the soil.

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Impacts of the change of LAI on transpiration and net photosynthesis of a single leaf and evapotranspiration (ET), net photosynthesis (CER) and water use efficiency (WUE_ET=CER ⁄ ET) of a whole canopy were evaluated at four growing stages of rice in a paddy field by the multilayer model. LAI was changed by multiplying the present vertical profile of leaf area density by 0.0 to 2.2, which coincides with LAI of 0 to 10 approximately. As the increase of LAI, ET and CER increased asymptotically, reached their maximum and decreased for more excessive LAI. This is because, as the increase of LAI, transpiration and net photosynthesis in the upper canopy layers increased asymptotically and decreased in the middle and lower layers and evaporation from water or soil beneath the canopy decreased asymptotically. These changes of ET and CER caused WUE_ET to increase asymptotically and reach its maximum. The maximum of ET, CER and WUE_ET or the optimum LAI for CER and WUE_ET tended to occur more easily at earlier or later hours in the daytime or under lower light condition. This is because solar radiation and PAR in the lower canopy layers decreased to less level by more mutual shading as LAI increased in these conditions. The optimum LAI for CER and WUE_ET on the four days were in the range of 5.0 to 10.0 and 5.8 to 10.0 respectively, which were different for crop stage, time and meteorological conditions. The optimum LAI for CER was little higher than those of other researches owing mainly to weather condition of higher solar radiation on the four days.

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A new chamber technique, based on the diffusion equation, is devised to measure gas fluxes emitted from the soil. The top of the chamber is made of a porous material of known diffusivity. We determine the fluxes passing through the porous media by measuring the concentration difference between the inside and outside of the chamber. The proposed method, the diffusion system or the porous-top chamber method, is a steady state method and able to measure the CO₂ fluxes from soil cores in the laboratory within the precision of the CO₂ sensor. Our system may provide a simple and economical means for continuous surface flux measurements in the field.

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