Effects of Climate Change on Soil Water Condition in Agricultural Lands in Japan.

According to AR5 by IPCC we will be required to consider fate of soil organic carbon to manage CO₂ concentration of atmosphere. Predicting future soil water condition of arable lands is important for mitigation as well as adaptation of climate change. General Circulation Models (GCM) have been developed all over the world, and GCM projections have been used for investigating impacts of climate change. For soil moisture prediction, both temporal and spatial scale of the input climate data had better be similar to those of soil water movement, a few kilometers in space and hourly or less in time. However, most of the available GCM projections have the spatial and temporal resolution of 100km and a month, respectively. In this study, we attempted a temporal downscale on GCM projections, and to simulate soil moisture condition of agricultural lands. Soybean fields of Toyama city, middle part of Japan facing Japan Sea were chosen as the experimental site, and scenario studies were conducted with HYDRUS model. The projections of MIROC-hires 3.2 A1B scenario were selected from “ELPIS-JP data set”, which is the scenario database of daily local-scaled GCM projections in Japan. The GCM projections were temporally downscaled to hourly or minutes scale by using the weather generator “CLIGEN” for simulation by HYDRUS. According to the climate scenario which was used in this study, both intensity and frequency of daily rainfall tend to increase especially in June. Simulated results suggested, for example, that excess soil moisture condition following heavy rainfall events are more likely to occur in the future than present, and this would affect initial growth stage of soybean even though highly water-permeable Sandy Loam is distributed in the study site.

Acknowledgement: This study was supported by Research Program on Climate Change Adaptation of Ministry of Education, Culture, Sports, Science and Technology.