Abstract
As the problem of climate change increases in importance, evaluations of its impact are urgently required.Through a series of studies, we estimated the impact of climate change on Japanese water resources using a waterresources model comprising five sub-modules: land surface hydrology, irrigation, rice growth, dam operation, andstream flow. The model has the benefits of simulating not only the natural water cycle on land but also rice yields and theeffects of human activities such as dam operations, water withdrawal, and irrigation. This paper presents the water resourcesmodel and verifies its accuracy for Japanese river basins. Using observed meteorological data during 1994-2003, we analyzedriver discharge, rice yields, and water stresses. The main results are as follows: （1) Simulated rice heading date,harvesting date, and yield agreed with the prefectural statistical data. （2) Estimated river discharges showed good agreementwith observed stream flow records in 20 first-grade rivers, with no parameter calibrations. The simulated data for riverdischarges were improved using a dam operation module and by correction for snowfall data. （3) Water stresses in Japaneseriver basins were computed by calculating the cumulative withdrawal to demand ratio （CWD). Calculated values showedgood agreement with a statistical drought map, suggesting that the CWD reflects actual water shortages in Japanese basins.
