Yoko Shibutani

Local amplification of storm surge by Super Typhoon Haiyan in Leyte Gulf

Typhoon Haiyan, which struck the Philippines in November 2013, was an extremely intense tropical cyclone that had a catastrophic impact. The minimum central pressure of Typhoon Haiyan was 895 hPa, making it the strongest typhoon to make landfall on a major island in the western North Pacific Ocean. The characteristics of Typhoon Haiyan and its related storm surge are estimated by numerical experiments using numerical weather prediction models and a storm surge model. Based on the analysis of best hindcast results, the storm surge level was 5–6 m and local amplification of water surface elevation due to seiche was found to be significant inside Leyte Gulf. The numerical experiments show the coherent structure of the storm surge profile due to the specific bathymetry of Leyte Gulf and the Philippines Trench as a major contributor to the disaster in Tacloban. The numerical results also indicated the sensitivity of storm surge forecast.

Climate change effects on the worst-case storm surge: a case study of Typhoon Haiyan

Effects of climate change on the worst case scenario of a storm surge induced by a super typhoon in the present climate are investigated through the case study of Typhoon Haiyan. We present the results of our investigation on super-typhoon Haiyan by using a super high resolution (1 km grid) regional model that explicitly handles cloud microphysical processes. As the parent model, we adopted the operational weekly ensemble experiments (60 km grid) of the Japan Meteorological Agency, and compared experiments using sea surface temperatures and atmospheric environmental parameters from before the beginning of anthropogenic climate change (150 years ago) with those using observed values throughout the typhoon. We were able not only to represent the typhoons intensity but also to evaluate the influences of climate change on worst case storm surges in the Gulf of Leyte due to a typhoon with high robustness. In 15 of 16 ensemble experiments, the intensity of the simulated worst case storm in the actual conditions was stronger than that in a hypothetical natural condition without historical anthropogenic forcing during the past 150 years. The intensity of the typhoon is translated to a disaster metric by simulating the storm surge height by using a shallow-water long-wave model. The result indicates that the worst case scenario of a storm surge in the Gulf of Leyte may be worse by 20%, though changes in frequency of such events are not accounted for here.

Estimation of property loss and business interruption loss caused by storm surge inundation due to climate change: a case of Typhoon Vera revisit

Abstract This paper estimates property loss and business interruption loss under scenarios of storm surge inundation to explore the economic impact of climate change on Ise Bay, Japan. Scenarios-based analyses are conducted with respect to Typhoon Vera, which caused the most severe storm surge in the recorded history of Japan in 1959. Four different hazard scenarios are chosen from a series of typhoon storm surge inundation simulations: Typhoon Vera’s landfall with respect to the condition of the past seawall; Typhoon Vera’s landfall with respect to the condition of the current seawall; intensifying Typhoon Vera, but retaining its original tracks; and intensifying Typhoon Vera, but choosing the worst tracks from various possible typhoon tracks. Our economic loss estimation takes advantage of fine geographical scale census and economic census data that enable us to understand the spatial distribution of property loss and business interruption loss as well as identify the most potentially affected areas and business sectors on a sub-city scale. By comparing the property loss and business interruption loss caused by different hazard scenarios, the effect of different seawalls is evaluated and the economic impact of future climate change is estimated. The results indicate that although the current seawall can considerably reduce the scale of losses, climate change can cause Ise Bay to experience more serious storm surge inundation. Moreover, the resulting economic losses would increase significantly owing to a combination of climate change and the worst track scenario. It is, therefore, necessary to consider more countermeasures to adapt to climate change in this area.

Effect of the Coastal Protection using the Beach Nourishment at Tottori Sand Dune Coast, JAPAN

ABSTRACT Shibutani, Y.; Kuroiwa, M.; and Matsubara, Y., 2016. Effect of the Coastal Protection using the Beach Nourishment at Tottori Sand Dune Coast, JAPAN., Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 695–699. Coconut Creek (Florida), ISSN 0749-0208. Beach erosion is a serious problem worldwide. The Tottori Sand Dune coast had started eroded in the 1950s, and the beach nourishment project has been carried out to restore the shoreline since 2005. The total volume of the sand was approximately 650,000 m3 from 2005 to 2014. In particular, a large amount of sediments, which was 100,000 m3, was injected in 2010 and 2011. In this study, the effect of the project was estimated. The sand volume increased temporarily after the large-scale beach nourishment, and then, the sand volume gradually decreased. However, the shorelines showed restoration trends after the beach nourishment project. In addition, although a part of the injected sediments was moved to the Tottori port, recovery of the shoreline was maintained.

N-Line Model for Predicting Beach Evolution due to Nourished Sands

A numerical beach evolution model, which can predict depth contour line change due to beach nourishment, was proposed. The effect of beach nourishment was taken into account by solving two- dimensional advection diffusion equation for nourished sand material. Some model tests of beach evolution due to nourishment were performed. Furthermore, the new N-line model was applied to preservation of eroded beach using a sand recycle method measures, and then the performance of the model was investigated.

Projection of decrease in Japanese beaches due to climate change using a geographic database

ABSTRACT This study models shoreline retreat due to sea level rise by using geographic data and applies the model to future projections of decreases in beach area for 806 beaches in Japan. The model uses a foreshore slope (angle) based on data from a digital elevation model, and influence of the present simplified method for estimation of the shoreline retreat is examined through comparisons with previous studies at typical locations. The proposed method gives a distance of shoreline retreat due to sea level rise similar to that predicted using the Bruun rule for minimal retreat less than 30 m, but the difference becomes substantial for more extensive decreases. The decrease in beach area is projected for different sea level rises based on four Representative Concentration Pathway (RCP) scenarios from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. The decrease in beach area becomes more severe for the RCP8.5 scenario, and the proposed method predicts that a third of current sandy beaches in Japan will disappear. The extent of the decrease depends not only on the sea-level-rise scenario but also on the SLR projection model.

3D Morphodynamic Modeling of a Sand Recycling System

ABSTRACT Yasumoto, Y.; Kuroiwa, M.; Shibutani, Y.; Osakada, Y., and Matsubara, Y., 2016. 3D morphodynamic model for sand recycling system. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 502–506. Coconut Creek (Florida), ISSN 0749-0208. Sand nourishment such as sand bypassing or sand recycling is an effective measure against beach erosion as an alternative technique. The method for setting the optimum injecting amount, site and running cost has not been developed. A numerical model considering the sand nourishment is needed to evaluate the performance of the sand recycling and bypassing projects. This paper is concerned with the development of 3D beach evolution model for taking account the sand dredging and injection processes. In this paper, a model test for sand recycling in an area with artificial reefs was carried out. The model was applied to a sand recycling project conducted at a field site with five artificial reefs (an erosion area). The applicability against the morphodynamics around the five artificial reefs was investigated. Although the volume of erosion/deposition behind the artificial reefs was overestimated, the developed numerical model qualitatively agreed with the measured bathymetry.

Applicability of 3D Beach Evolution Model with Wave-current Interaction to River-mouth Bar Formation

ABSTRACT Kuroiwa, M.; Shibutani, Y.; Yasumoto,; Mase, H, and Matsubara, Y., 2016. Applicability of 3D beach evolution model with wave-current interaction to river-mouth bar formation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 73–77. Coconut Creek (Florida), ISSN 0749-0208. A coastal area model with wave-current interaction was presented, and then the performance and applicability of the numerical to morphodynamics around river mouths due to waves, wave-induced currents and river flows were investigated. First, model tests were carried out under a variety of wave and river discharge conditions to investigate their capability of predicting the formation of sand spit and terrace topographies. Second, model verification using a field site was conducted and the applicability was investigated. From the computed results, it was confirmed that the prediction of presented model had good qualitative agreement with an actual sand spit formation.