Assessment of climate change impacts on river discharge in Japan using the super-high-resolution MRI-AGCM

To evaluate the impacts of climate change on river discharge, we applied a hydrological simulation to several major river basins in Japan, using a super-high-resolution atmospheric general circulation model (AGCM) with a horizontal resolution of about 20 km that was developed by the Meteorological Research Institute (MRI) of the Japan Meteorological Agency. For our analysis, we used two AGCM datasets corresponding to the current climate (1980-1999) and future climate (2080-2099) based on the sea surface temperature ensemble projected by the Coupled Model Intercomparison Project phase 3, assuming the A1B scenario of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. River discharge was estimated using a distributed hydrological model that was calibrated in advance with observed river discharge. We investigated the impact of climate change on river discharge by comparing hydrological simulations of current and future climate conditions. The results showed that the latest version of the AGCM (MRI-AGCM3.2S) performs better hydrological simulations than the previous version (MRI-AGCM3.1S). Even if the amount of precipitation does not change greatly in the future, river discharges will change significantly as air temperature rises, owing to increased rainfall, decreased snowmelt, and increased evapotranspiration. The impact of climate change on river discharge will become more significant in northern Japan, especially in the Tohoku and Hokuriku regions. Our results imply that the increase in air temperature will have important consequences on the hydrological cycle, particularly in regions where the water supply is currently domi\nated by snowmelt. Copyright (c) 2013 John Wiley & Sons, Ltd.