Influence on Rice Production in Japan from Cool and Hot Summers after Global Warming

摘要

A cool summer seriously damages rice production in Japan under the present climate. On the other hand, an extremely hot summer may reduce production because of heat stress during the flowering period in a post-global warming climate. Reliable impact projections are required to grasp the hazards of production variability. However, accuracy limitations of the General Circulation Model (GCM) products obstruct impact projections in a particularly extreme year. A new dynamic downscaling method is suggested by the current study, which contributes to estimating a higher-resolution climate from GCM products while reducing the GCM bias. The bias means the difference between the simulated value and observations, and is the most serious factor in decreasing the reliability of impact projections. This study aims to show the difference in (1) the region-scale climate change and (2) the influence on rice production between a cool summer year and a hot summer year after global warming. A Regional Climate Model (RCM) downscales the change in climate over Japan based on GCM products under the Special Report for Emission Scenario-A2 scenario. Simulated changes in daily maximum/minimum temperatures, daily total solar radiation and monthly total precipitation vary depending on the target month and the area. Crop model simulations show that climate changes reduce the damage caused by a cool summer throughout Japan. On the other hand, climate changes enhance the damage caused by heat stress in central to southwesternJapan, but the damage is not found in northern Japan even in a hot summer year. As the result of global warming, the damage to yield from a cool summer is mitigated; however, damage from heat stress is enlarged in a post-global warming climate.