Abstract
This study estimated the impacts of climate change on Japanese water resources using a hydrological model proposed in an earlier study. Using forcing outputs from a super high-resolution global climate model (MRIAGCM3.1S), we analyzed river discharge, rice yields, and water stresses under present (1979-2003), and anticipated nearfuture (2015-2039) and late 21st century (2075-2099) climates. The main findings were the following: (1) Climate change will engender large changes in seasonal discharge in basins facing the Sea of Japan, which experience heavy snowfall. Snowfall depletion will increase winter discharge and decrease spring discharge. (2) Changes in water stress were evaluated by calculating the cumulative withdrawal to demand ratio (CWD). Water stress will increase despite the increase in water resources in many basins, especially in the Tohoku District. Results show that many Japanese basins will face severe challenges in water resource management under future climate scenarios. (3) Warm temperature trends will cause rice yields to increase in northern, eastern, and central Japan. Under climatic conditions predicted for the end of the century, late plantings will be a necessary adaptation to avoid high-temperature and low-temperature damage in northern and western Japan. However, late plantings will also negatively affect yields by increasing water stress in basins in the Tohoku District that experience heavy snowfalls.
