The Flood Vulnerability Index (FVI) is an index for assessing vulnerability to flood disasters that can be applied at the river basin level. The main objective of FVI is to be useful as versatile applications for policy-making on flood disasters by governmental decision makers. FVI can also be used to raise public awareness about flood disasters. FVI consists of a rainfall factor, which may be one of key factors of flood disaster and is regarded as Climatic component, and also three components: Hydro-geographical, Socio-economic and Countermeasures. In this study, 114 major river basins around the world were assessed with the use of FVI. These major components were divided into 11 indicators (sub-components) which were selected based on factor diagram analysis in terms of flood disaster. Then FVI values were estimated using the multiple linear regression analysis for these major river basins based on three explanatory variables: "Frequency of heavy rainfall", "Average slope of basin", and "Urbanized area ratio in basin".

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Hydrometric observation was conducted at the coniferous catchment (1.29 ha) and the deciduous catchment (1.28 ha) in order to reveal the effects of tree species on stormflow generation processes. Runoff response of overland flow was large and responded to individual peaks of rainfall intensity at the cypress plot, however it was very small at the deciduous plot. It was inferred that overland flow from the cypress plot was root-flow (shallow preferential flow through the root layer of the Japanese cypress forests) and it from the deciduous plot was litter flow, because overland flow occurred at the both plots during lower rainfall intensities than final infiltration rate. Hydrological response and the contributions of 'Non-reacted water' increased remarkably as the storm size become larger (P ≥ 100 mm). The ratio of "Non-reacted water" to discharge peaks were 40∼50 percent at the both catchments during the large typhoon storm (P:117.4 mm) . The storm size would cause drastic changes in main component of "Non-reacted water". Hydrograph separation by Si suggested that "Non-reacted water" was mainly composed of root-flow and shallow subsurface flow at the coniferous catchment, and it was composed of shallow subsurface flow at the deciduous catchment.

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We describe the hourly changes of discharge for one day on the Nakadori River, which functions as a main drain for an irrigated paddy field of the Fukuoka-zeki Irrigation Project, Ibaraki Prefecture, Japan, and analyze the reasons for the changes. The catchment area of the river is 2,267 ha, of which 1,221 ha is a well-consolidated paddy field that has independent access to irrigation and drainage ditches at the plot level. We observed the water level in the river every 30 minutes using a pressure-sensor type water-level recorder from 2004 to 2006, and found a stable rate of hourly change each day, with the maximum around at 6:00 and the minimum around 18:00 during dry spells. We have also measured water levels at different levels of drainage, including a lateral drainage canal and a farm drain canal in the catchment area. Using evapotranspiration data obtained in a nearby paddy field, we performed a quantitative analysis of discharge flow and estimated evapotranspiration, obtaining the following results: i) The same pattern of changing water level or discharge in the Nakadori River is seen at all canal levels in the drainage system. ii) The increase in the evapotranspiration temporally coincides with that in the discharge, and the quantity of the former is accountable to the latter, as well. iii) The hourly change of discharge in the drain is caused by evapotranspiration through its influence on water level in the plots under a constant water supply to the paddy plots.

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