We aimed to develop a simple method to predict regional variation in nitrogen loss potentials from forested area in the forested Yahagi River watershed (1,340 km²) in central Japan.
Firstly, we estimated within the watershed variation in nitrogen loss potentials through the following three processes: (1) We investigated the net nitrification rate of surface mineral soils using aerobic laboratory incubation at 30 °C for 4 weeks (mg N⋅kg soil^-1⋅28 d^-1); (2) we developed a multiple regression model to predict the net nitrification potential on a per-area basis for surface (0-5 cm) mineral soils (Mg N⋅km^-2) from only geographical factors; (3) we predicted the regional variation in the net nitrification potential using available GIS data as explanatory variables.
Secondly, we estimated annual outflow using a combination of a GIS model and a simplified evapotranspiration model. We examined accuracy of the model for estimation of annual outflow by comparing values predicted by the model with values measured at two outflow survey points.
Finally, we estimated nitrate concentration potentials in stream water defined as the net nitrification potential divided by annual discharge (mg N⋅L^-1) as an index of regional river water quality. We verified that a series of GIS prediction technique could produce the regional trend in measured nitrate concentrations.

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The soil microtopography has a great impact on soil-water interactions during rainfall. The objectives of this study were to develop methods to rectify the digital elevation model (DEM) generated by the automated digital photogrammetry system and to apply these methods in monitoring the changes in soil microtopography during rainfall. Two rectification methods were used in order to detect and eliminate the DEM errors. The first method was the reference surface method (RSM), which was developed as a part of this study to detect the DEM errors prior to interpolation. The second was the parametric statistical method (PSM), which was used to detect and rectify the DEM errors after interpolation. The DEMs accuracy was assessed using the difference between the measured and photogrammetrically estimated checkpoints coordinate and elevation (x, y and z, respectively) values. The root mean square error (RMSE) in x-direction, y-direction and z-direction of the checkpoints were 2.08, 2.59 and 1.96 mm, respectively. The changes on the soil surface were assessed using three roughness indices. The soil surface random roughness (RR), the limited elevation difference (LD) and the limited slope (LS) indices decreased with the time. The automated digital photogrammetric system with the rectification methods accurately generated three dimensional (3D) visions of the soil microtopography during rainfall. It gives a new insight for monitoring the changes of soil microtopography and the effects on soil-water interaction processes.

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The behavior of rain water that reached the forest floor during a large scale rainfall event was clarified on a mid-lower position of slope in a natural forest, western Kochi, an area known for heavy rainfall, in order to discuss the influence of such water movement on nutrient dynamics or occurrence of the landcollapse. Throughfall, the overland flow, the soil water storage of 0 to 50 cm in depth, and the output of a tension-free lysimeter (TFL runoff) at 50 cm in depth were observed during two events with a total rainfall 642 mm (2005/9/4-7) and 355 mm (2006/8/16-19). Near the research site, the precipitation and the catchment runoff were also observed. We found that the runoff percentage of the overland flow to the throughfall was low, and the upper limit (about 60 mm) for an increase of the soil water storage during an event(ΔS) was determined. After ΔS exceeded about 40 mm, the TFL runoff demonstrated that about 70 % of throughfall drained to soil layer deeper than 50 cm at almost same intensity and time (delay within 30 minutes) as throughfall. The peaks of catchment runoff occurred at almost the same time as those of throughfall and the TFL runoff. Therefore, the subsurface stormflow, not the overland flow or the soil water storage, was important for runoff processes in large scale events, suggesting that the subsurface stormflow contributes to the formation of the direct runoff. The above indicates possibilities that the fast subsurface stormflow prevents the landcollapse and runoff to stream under little reaction to soil or bedrock during an event.

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Although Japan has made huge amount of international contribution under UN oriented foreign policy, it has not been appropriately appreciated. However, the UN World Water Assessment Programme (WWAP) that was established in August 2000 under Japan's leadership launched the World Water Development Report (WWDR) in March 2003, and continues developing with high appreciation from both developed and developing countries as the first UN System-wide programme on water resources. Its success has been greatly contributing to significant presence of Japan and the analysis of its development has identified key factors that a UN programme on water resources under Japan's leadership can effectively functions. They are: 1) political leadership, 2) multilateral framework, 3) UN System-wide scheme, 4) governmental ownership and initiative, and 5) effective media strategy.

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Important studies on water cycle processes using stable isotope of water were reviewed. The objective papers on the global-scale water cycle were studies including isotopic ratios of ocean surface water and those of water vapor over the ocean as well as studies on atmospheric circulations using AGCM (atmospheric general circulation model) with stable isotope of water. Regional-scale studies on runoff processes, evapotranspiration or vegetation-related processes, and meso-scale precipitation processes were also revisited. Additionally studies on the paleoclimate and cryospheric processes, which closely related to temporal variations of water cycle processes, were focused. Finally, perspectives on the water cycle study using stable isotope of water were summarized.

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