Estimation of the Impact of Climate Change on Japanese Rice Yield and Water Resources

The aim of this study is to estimate the impact of climate change on Japanese rice yield and water resources using a newly-developed Japanese Water Resources Model. The model is composed of five sub-modules: land surface hydrology, irrigation, rice growth, dam operation, and stream flow. Using observed meteorological data for the period of 1994 to 2003, simulated river discharge and rice yields were verified. We estimate impact of climate change on river discharge, rice yields and water stress using bias-corrected outputs from a super high-resolution global climate model under present, near-future, and late 21st century climate conditions. The main findings were as follows: (1) Simulated rice yield and river discharge using observed meteorological forcings have shown good agreement with statistical data. The snowfall correction and the dam operation module clearly improve the simulated river discharge. (2) The seasonal discharge will change dramatically, especially at the end of the 21st century, in basins facing the Sea of Japan that currently experience heavy snowfall. A depletion of annual snowfall would be result from the warming temperature trend in many basins. (3) Climate change is predicted to strengthen the water stress in many basins in the northeastern Japan, which uses large amounts of snowmelt water to prepare rice paddies for planting. Water stress would also increase in small basins. (4) Climate change may mitigate low-temperature stress and expand the arable area, including into high-mountain areas and northern prefectures. Many prefectures facing the Sea of Japan are predicted to experience decrease in rice yield. The simulation clearly demonstrates the regions that should consider changing the period of cultivation to mitigate the decrease in rice yields and increased water stress.