Estimation of cool summer damage in the Tohoku region based on the MRI AGCM

Abstract

We analyzed the impact of climate change due to global warming on the risk of cool summer damage to paddy rice in the Tohoku region of Japan. We downscaled the atmospheric general circulation model of the Meteorological Research Institute (MRI AGCM) to 10 km, and we used monthly average temperatures and their standard deviations to correct the bias of the simulated temperatures. We did not use daily averaged temperatures to determine the risk of cool summer damage. Instead, we used the cooling degree calculated from the average daily temperature over a period of time (CDAT). We also used the standardized yield calculated from temperatures during the month preceding heading. An examination of the reproducibility of cooling damage occurring under the current climate was based on bias-corrected data which revealed that although the simulated risk of cool summer damage slightly underestimated both the CDAT and the standardized yield, the areal distributions of risk were similar to those in years of cool summer damage. We assumed that the heading stage occurred 15.6 days earlier than current climate because of the impact of temperature increase under the future climate and therefore calculated the CDAT and standardized yield by advancing the critical period by half a month. During the secondand third-coolest summers under the future climate scenario, the risk of cool summer damage decreased in the southern Tohoku region facing the Pacific Ocean and in Aomori Prefecture on the Japan Sea side, but the risk of cool summer damage was almost the same as during the observed cool summer of 1980. In summary, our results revealed that under a future climate, simulated by the MRI AGCM, the risk of cool summer damage will persist in the Tohoku region; risk management for cool summer damage will therefore be essential, even though global temperatures rise.