Flood Simulations in Mid-Latitude Agricultural Land Using Regional Current and Future Extreme Weathers

Recent extreme weather events like the August 2016 flood disaster have significantly affected farmland in mid-latitude regions like the Tokachi River (TR) watershed, the most productive farmland in Japan. The August 2016 flood disaster was caused by multiple typhoons that occurred in the span of two weeks and dealt catastrophic damage to agricultural land. This disaster was the focus of our flood model simulations. For the hydrological model input, the rainfall data with 0.04° grid space and an hourly interval were provided by a regional climate model (RCM) during the period of multiple typhoon occurrences. The high-resolution data can take account of the geographic effects, hardly reproduced by ordinary RCMs. The rainfall data drove a conceptual, distributed rainfall–runoff model, embedded in the integrated flood analysis system. The rainfall–runoff model provided discharges along rivers over the TR watershed. The RCM also provided future rainfall data with pseudo-global warming climate, assuming that the August 2016 disaster could reoccur again in the late 21st century. The future rainfall data were used to conduct a future flood simulation. With bias corrections, current and future flood simulations showed the potential inundated areas along riverbanks based on flood risk levels. The crop field-based agricultural losses in both simulations were estimated. The future cost may be two to three times higher as indicated by slightly higher simulated future discharge peaks in tributaries

Regional Climate Projection Experiments on the Baiu Frontal Activity around the Japan Islands Using a Non-Hydrostatic Cloud-System-Resolving Model

Abstract Regional climate experiments focusing on the Baiu frontal precipitation were performed on the Earth Simulator using a non-hydrostatic cloud-system-resolving atmospheric model (NHM) with a horizontal resolution of 5 km (5km-NHM) and 1 km (1km-NHM). The outputs of an atmospheric general circulation model (AGCM) with a horizontal resolution of about 20 km were used as the boundary of 5km-NHM. The time-slice method in both the present and future climates was applied for the experiments of the AGCM and NHM. In the present climate experiments, it was evaluated that the precipitation distribution and precipitation frequency spectrum (PFS; frequency with intensities) of the 5km-NHM were well reproduced in comparison with those observed. Here, the AGCM in the present climate well reproduced the large-scale characteristics of the Baiu frontal precipitation. The Intergovernmental Panel on Climate Change (IPCC) A1B CO2 emission scenario was used to project changes in the precipitation property around the Baiu front due to global warm-ing in the future climate around the end of the 21st Century. The 5km-NHM projects not only an increase in precipitation around Western Japan associated with the elongation of the Baiu front due to global warming but also an intensification of precipitation associated with the enhancement of the convectively unstable strat-ification. The 1km-NHM experiment demonstrates the effects of the high resolution and shows further quality improvements of the PFS and higher reproducibility of extreme precipitation events associated with th