INFLUENCE OF TERRAIN MODEL IN 5KM DYNAMICAL DOWNSCALING OF JRA-55 ON FLOOD RUNOFF ANALYSIS

The purpose of this research is to investigate the influence of selection of terrain model on the flood runoff analysis due to the spatial distribution and magnitude of rainfall when performing double-nested dynamical down scaling from regional climate model with horizontal resolution of 20 km. Based on JRA-55, two levels of nesting with horizontal grid spacing of 20 km and 5 km were performed. In the 5 km experiments, the Grid mean model and the Envelope Mountain model were employed as the terrain model. The flood runoff analysis in the Nagara River was conducted using results of these climate models as input conditions. In the Envelope Mountain model, it was confirmed that many precipitation concentrates at the edge of the mountainous area, and the precipitation amount in the inland area decreases. In the Nagara River basin, the precipitation amount and the flood peak flow rate were clearly overestimated. The importance of choice of terrain model in 5 km regional climate model on flood-runoff analysis was presented.