A new runoff model was proposed based on the results of a study in which storm runoff responses were determined mainly from vertical unsaturated flow. Application of this model to three small mountainous catchments yielded good results for storm-runoff responses. These results suggest that soil-layer depth and soil physical properties play dominant roles in storm runoff responses. Runoff mechanisms were reevaluated based on model-application results and earlier observation studies. The variable source area concept was examined first: the runoff rate was quite low when the areas with wet condition in the entire soil layer were still horizontally isolated, but a high rate was achieved after the wet areas became mutually connected. A good simulation result obtained from the model application until landslide occurrence in a zero-order catchment suggests that presumably vertical water flow strongly affects storm runoff responses because the high groundwater drainage capacity is sufficient to maintain soil layer stability for several hundreds of years. Observed storm runoff rates from a weathered granite catchment with a large storage capacity in the bedrock were well simulated by about half of the rate calculated using the runoff model. This result suggests that the storm runoff response through the downslope flow might derive from the lower zone of catchment where the vertical unsaturated flow was intercepted by the shallow groundwater.

　The feasibility of ensemble reforecast data in dam operations was investigated for the heavy precipitation event of July 2018. Analysis of rainfall forecasts by an ensemble prediction system suggested that it might have been possible to identify a signal of significant precipitation six days before the time of peak discharge at the Kanogawa Dam and a high probability of significant precipitation (kind of precipitation that occurs once every 50 years) three days before the time of peak discharge. It is difficult to foresee a probability of great amounts of precipitation soley by observing the forecast by the control member of the ensemble forecasts or the forecasts by the high-resolution global model. Anticipating various possible scenarios from the results of multiple forecasts by the ensembles is important. In this case, by comparing the ensemble forecast results with the model climate values from the reforecast data, the probability of occurrence of significant meteorological phenomena can be estimated more quantitatively. The reforecast data are useful as a reference for effective dam management and its decision-making such as pre-release operation.

　Established in March 2006 as a UNESCO Category II Centre, the International Centre on Water Hazard and Risk Management (ICHARM) has been implementing three-pillar activities of research, training and information networking by application of a three-in-one approach to close interlinking of all three areas to create synergic effects among them. This report describes three cases to explain ICHARM’s signature activities: (1) international technical cooperation on flood hazard mapping; (2) support using the scheme of the International Flood Initiative (IFI); and (3) international technical interaction through human resource development, including training and networking. This report also presents analyses of synergic effects arising from mutual interaction among research, training, and networking when implemented in a three-in-one manner. Finally, the findings suggest future directions of these activities through elucidation of such issues as new project development, promotion of new regional partnerships and networking, and the fostering of facilitators capable of providing technical advice and solving local problems.