2023 Volume 14 Issue 2 Pages 100-106
In this study, we analyzed the reduction in snowfall and snowmelt under climate change scenarios in a cold snowy region. Also, we clarified the causal relationship between deforestation and disaster risk in watershed management in Mishima Town, Fukushima Prefecture. We used SWAT+ to conduct simulations; the SWAT+ model of Mishima town was built in a previous study, and its reproducibility was verified by NSE and RMSE by correcting parameters and using auto-calibration. The latest set of models from the CMIP6, also used in the 6th Impact Assessment Report of the IPCC and statistically downscaled scenarios in Japan developed by the Center for Climate Change Adaptation, National Institute for Environmental Studies, was adapted to simulate climate change scenarios. The Emission Scenarios are based on RCP8.5, which has been used in future climate change discussions (i.e., the assumption that greenhouse gases will continue to increase without any global warming countermeasures). We simulated the end of the 21st century situation. As the result of the simulation, the RCP8.5 scenario showed a significant decrease in snowfall and snowmelt, with only one day of snowfall of RCP8.5 from January to March. The potential for early spring snowmelt water availability of RCP8.5 at the end of the 21st century could have been much higher. Additionally, we conducted a simulation of deforestation. We assumed that 5 % of the forested area became agricultural land due to deforestation. Simulation results indicated that the surface flow under deforestation conditions was 145.1 mm, a 7 % increase over the surface flow of the original forest prior to deforestation (135.1 mm). Heavy and long-lasting rainfall showed no difference in water storage function between the two cases, but 5 % deforestation was shown to increase river discharge at the beginning of a rainfall event.
