[A-CG34] Projection and detection of global environmental change

[ACG34-P05] Dynamical downscaling of future sea level change around Japan using high-resolution ocean model

*Tatsuo Suzuki¹, Yoko Yamagami¹, Hiroaki Tatebe¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:Sea level change, Dynamical downscaling, Global warming, Kuroshio Current

Sea level rise is one of the most apparent manifestations of global warming, and it directly threatens coastal areas due to increased erosion and more frequent storm-surge flooding. Results from Global Climate Models (GCMs), such as those involved in CMIP6, have played an important role in informing diverse assessments of future impacts of climate change. However, the raw outputs are insufficient to address the issues of concern to stakeholders. The two primary impediments to impact studies are that the spatial scale of the GCMs may not be as fine as end users require and that the raw output is likely to contain biases relative to observed data, requiring some bias correction. Since increasing the resolution of GCMs requires considerable computational resources and may not improve regional biases, downscaling techniques are required to use GCM outputs in impact assessment studies. Therefore, Nishikawa et al. (2021) integrated a high-resolution regional ocean model for impact assessment studies of the Japanese coastal area with boundary conditions for outputs of CMIP GCMs. They created a 2km mesh high-resolution oceanographic dataset to assess the effects of global warming. However, as their model is directly forced by GCM outputs with biases in the meridional position of the westerly jet, the dataset includes climatological biases in the Kuroshio current pathways. To mitigate this climatological bias, we used the observation-based atmospheric reanalysis data (JRA55-do) as a boundary condition to simulate a high-resolution ocean model (COCO5 with 10km horizontal resolution) and added future warming anomalies from GCMs as a boundary condition to assess the impact of warming. The anomalies for future warming are estimated as the difference between the climatological values of the historical experiment (1981-2010) and the climatological values during 2081-2100 (4℃ warming experiment) and 2041-2060 (2℃ warming experiment) for the SSP585 scenario of MIROC6. Note that the interannual variability in this experiment remains the same as in JRA55-do and does not include modification of interannual variability due to global warming. The large-scale sea level response around Japan in this simulation is consistent with the results of the CMIP6 model ensemble, but the response is sharper around the Kuroshio Current. Details will be shown in the presentation.