Relationship between evapotranspiration and NDVI is discussed using the single layer model with physical process in the Natori River basin. A new algorithm is developed to make cloud free images of NDVI in time series. Distributions of albedo, wind speed, and interception are involved in the single layer model, which provides evapotranspiration distribution to compare with NDVI. As the results, the correlation coefficient of evapotranspiration estimated by the single layer model and the liner relationship method is more than 0.9, some regions having low and high NDVI do not have good agreements, and the applicable time period of the linear relationship is more than 1 month. Totally, the liner relationship can make us satisfy the estimation of evapotranspiration distribution.

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A method of potential river healthiness evaluation has been developed in the Natori River supported by GIS and a distributed hydrological model. We have proposed two indices, water quality index and river discharge index, which involve land use effects and distributed runoff model outputs, respectively. These indices can express well regional river environment. Using two indices, we could obtain more detailed information on river health and compare with other rivers having different precipitation. These indices are highly correlated with population density and forest covered ratio, which are convenient for general use. As the results evaluating other rivers from these indices, we could realize the difference among rivers in views of quality and quantity, and the effect of the river healthiness evaluation proposed.

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In order to implement policy measures on practical water management related to flood and drought to combat the influences of rainfall characteristic variation arising from global warming, quantitative indicators of future regional-based flood and drought risks are required. In this study, changes of regional-based flood and drought risks arising from global warming are analyzed based on the precipitation observation records obtained in Japan over the past 100 years, the effectiveness of the risk assessment is evaluated using the results of the regional climate change prediction over the next 50 years from the RCM20 regional climate change models developed by the Japan Meteorological Agency (JMA) and the Meteorological Research Institute (MRI), and then changes of regional-based flood and drought risks are forecasted. This study was carried out under the Global Warming Research Initiative of the Council for Science and Technology Policy, the Cabinet Office of Japan.

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This case study aims at development of a local remote sensing technology for measurement of surface flow field of rivers and rakes by means of PTV, Particle Tracking Velocimetry. Six thousand flat rice cakes with the diameter of 15 cm were scattered on the Uji river as tracers. A video camera mounted on a helicopter, hovering at the height of 300 m, took continuous images of the flow. Many problems associated with the practical applications of PTV to natural flow fields were picked up. Among them, there was a problem in identification of tracer images in that the computer software could not separate images of light reflections due to wind-driven surface tension waves from the tracer images. Countermeasures to the problems were proposed and tested. The surface flow field was analyzed by the PTV with the countermeasures, and compared with the flow field at 20-cm below the surface measured with an ADCP, Acoustic Doppler Current Profiler.

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During floods, dunes formed under the condition of a low discharge disappear when the discharge becomes larger than a certain amount, and dunes are re-created with decreasing discharge. On the dune-flat bed transition, it is observed that a critical discharge from dune to flat bed regimes is larger than a discharge from flat bed to dune regimes (hysteresis). The authors have shown that the dune-flat bed transition is characterized by subcritical bifurcation that causes hysteresis with the use of a nonlinear stability analysis. However, the critical Froude number at the dune-flat bed transition predicted in the analysis is much larger than that observed in the field. In this study, we performed a weakly nonlinear analysis incorporated with suspended sediment transport. It is found that the critical Froude number decreases due to the effects of suspended load while the transition is still characterized by subcritical bifurcation.

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Sea pollution caused by the red soil erosion has been becoming as an important social issue for Okinawa Islands, which are popular for subtropical ocean tourism. And also the establishment of an efficient countermeasure against the pollution has been required. In this research, the fundamental fluid motion of a rain droplet and the soil erosions caused by a rain droplet impact are studied experimentally. Three characteristic impact patterns of a rain droplet onto the ground surface are shown. Erosion processes in two different characteristic soil categories namely; Kunigami-margi and Shimajiri-margi that are chiefly distributed in Okinawa Islands are discussed.

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We ascertained residents' needs and wishes about a project for improving a river environment, using a questionnaire submitted to nearby residents. We used the results of the questionnaire, analyzed by conjoint analysis, as the basis for a draft improvement proposal. The cost of the improvements was then calculated and the proposal was analyzed using cost-benefits analysis. As a result, we found that, since all of the extensive plan for improving the quality of the river environment could not be performed, it was most important to found the following aspects of the proposal: 1) making the revetment comfortable to approach and giving it a natural appearance and 2) providing street lighting for safety.

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As simulated with the MHI oceanic model (Shapiro, 1998), surface gradient currents in the entire Japan Sea strengthen (weaken) in late summer (winter), with the highest (lowest) velocity in August (February), in line with altimetry data (Morimoto and Yanagi, 2001). The simulated patterns of the surface circulation are in line with those derived from satellite imagery (Nikitin and Kharchenko, 2002). In particular, a northern meander of the East Korean Warm Current is simulated near the North Korea coast in October, caused by local anticyclonic wind stress curl. The simulated deep circulation is geostrophic and reaches the highest (lowest) velocity in April (November), after 2 to 3 months of the extreme surface velocity.

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This study investigates characteristics of water temperature variations in the middle reaches of the Shinano River. Attention is given to the impact of a hydropower plant on downstream water temperature daily regime. Peculiar diurnal variation of water temperature appears immediately downstream of the power plant. At a different site, 17 km downstream of the power plant, thermal anomaly manifests in a different form that is designated herein as in-stream tropic night.

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