Shoreline Measurement for 30 Years and Projection by the End of This Century

Future sea level rise and change in the wave climate due to global climate change will cause dynamic coastal change. Coastal hazard risk such as wave over topping and inundation will increase in response to such changes in the external forces and beach morphology, which has become a social concern. In order to estimate the risk, projection of not only the average morphological change but also the temporary erosion during a storm is significant, therefore, we need a beach morphological change model with as high as possible time resolution. We hindcasted the daily measured shoreline position at the Hasaki coast of Japan from 1986 by an equilibrium-based shoreline change model. Using the model and the estimated model parameters, the shoreline position was projected by the end of this century under the future scenario of sea level rise and wave climate change. Limits of wave runup were also estimated in the present and the future for the risk analysis. As the result, the median position of the shoreline (H.W.L. contour) was projected to move approximately 10 m landward from the present position by 2095. Given the wave runup under the sea level rise and the wave climate change in the future, the future limit of the wave runup on an extreme event (exceedance probability: 1%) was estimated to reach 20 m landward from the present limit. These results are limited to the case study at the Hasaki coast, which is just local, but we will generalize the model to use for such projection in the various coasts globally. With the projection of the practical coastal response, we could consider the coastal adaptation plans to the climate change.