Climate Change Induced Morphological Response Assessment in Estuary: Case Study of Arakawa River Mouth, Niigata, Japan

Abstract

Morphological responses in estuaries are assumed to change in the future in association with changes in tidal levels, waves, and discharges under climate change. This study proposes a numerical modelling system for morphological changes in local estuaries to simulate hindcast and future scenarios considering futuristic tidal levels, waves, and discharges. The numerical modelling system configuration was based on three models: Weather Research and Forecasting model Hydrological modelling system (WRF-Hydro), Simulating WAves Nearshore (SWAN), and eXtreme beach behavior (XBeach). SSP5-8.5 and RCP8.5 were selected for constructing global warming environmental fields using the pseudo global warming (PGW) methodology. We conducted a numerical simulation of the morphological changes at the mouth of the Arakawa River during flood season. The hindcast simulation quantitatively reproduced the post-flood event sandbar topography by using boundary conditions of the simulated wave and observed discharge rate. Additionally, sea level rise, decrease in significant wave heights and mean wave periods, and increase in discharges were simulated for future simulations of the Arakawa River under climate change. The results considering future scenarios elucidated that characteristics of morphological responses changed compared with that of the present climate. Particularly, climate change enhanced the erosion effects since overflow due to rise in water level was more likely to occur at the river mouth sandbars. Hence, we suggest that the morphological response of estuaries to complex physical fields is sensitive to external force changes under climate change conditions.