Study on future storm surge around Suo-nada Sea

Japan lies on an area frequently hit by typhoons while city functions are clustered along the flat coastal areas, hence Japan has experienced lots of storm surge disasters up to the present. Coastal areas along the Suo-nada Sea also have the vulnerability against storm surge and in the past Typhoon 18 in 1999, Typhoon 16 and 18 in 2004 made remarkable damages in the areas. Furthermore, due to global warming, there are growing concerns about possible tremendous storm surge disasters caused by more furious typhoons than ever. Thus it is necessary to estimate the future storm surge for the coastal disaster prevention. The Suo-nada Sea, however, has some topographical factors which make storm surge estimations difficult. In this study, numerical simulations for storm surge around the Suo-nada Sea were performed by using a coastal circulation model FVCOM (Finite Volume Coastal Ocean Model) developed by Chen et al. (2003). FVCOM employs an unstructured grid system so as to accurately compute tidal currents even in complicated inner bays. First, appropriate computational domain was investigated. Then influences of various input data; calculation results by an empirical typhoon model, simulation results by a regional meteorological model and Grid Point Value, on the accuracy of simulations were examined. Next, future changes of typhoon characteristics around the sea area was investigated on the basis of Database for Policy Decision making for Future climate change (d4PDF). Finally, the future storm surge in Suo-nada Sea was estimated. From the simulations, it was found that more intense typhoons would strike the Suo-nada Sea and the direction of typhoon tracks would change toward the north in the future due to the global warming. It was also shown that the storm surge around the sea area can be more developed and cause more severe damages around the region in the future.Japan is an island nation and located on an area frequently struck by typhoons. And since most of Japan is occupied by mountains or hills, main city functions are clustered along a flat coastal area therefore Japan has experienced lots of coastal disasters up to the present. Suo-nada Sea which is located in Kyushu area, south part of Japan also has a vulnerability against storm surge though there are less investigations on storm surge in the sea area comparing to the three major bays in Japan or Ariake-Sea. However, due to sea level rising and more furious typhoons than ever caused by global warming, it is concerned that the storm surge disaster can be more severe in the future. Thus the investigation on future storm surge in the sea area is also strongly expected for future coastal disaster prevention. This study was carried out to investigate future storm surge in Suo-nada Sea and some numerical simulations were performed using ocean circulation model, FVCOM characterized by unstructured grids. Firstly, the most suitable computational domain size for estimating storm surge in Suo-nada Sea was found from the perspective of both simulation accuracy and computational efficiency. And also the simulation accuracy depending on the data types of external forces and typhoon tracks in the sea area was verified. Secondly the change of typhoon characteristics around the sea area in the future was evaluated with database for Policy Decision making for Future climate change. And it was known that major typhoon track around the region might be changed in the future and also the number of typhoon approaching to the region would be decreased whereas the ones with high intensity would be increased. And finally, with the strongest future typhoon approaching to the region extracted from d4PDF, future storm surge was estimated using an empirical typhoon model with more reality by considering typhoon’s fading by its traveling land area. And the risk of future storm surge in Suo-nada Sea was investigated. As a result, it was found that there would be a risk of storm surge developing more than present in the future especially at inner part of Suo-nada Sea