The present work evaluates potential future typhoon and storm surges around the islands of Samar and Leyte in the Philippines taking into account monthly mean sea surface temperatures, atmospheric air temperature, and relative humidity (hereafter, SST, AAT, and RH) from MIROC5 according to four scenarios proposed by IPCC AR5. Supertyphoon Haiyan (2013), which caused catastrophic damage to coastal areas in the Philippines due to its high winds and storm surge, was used as the case study storm given that it was one of the tropical cyclones recorded in modern history. In this study, the Advanced Research Weather Research and Forecasting Model (ARW-WRF) is used to estimate the characteristics of both the present-day Haiyan and a typhoon with a similar return period under the climate condition of the year 2100. The unstructured, Finite Volume Community Ocean Model (FVCOM) was used to estimate both the present and potential future storm surges. The research has two main focuses. First, both the historical event and its storm surge are simulated and contrasted with field measurements of the storm surge height in order to prove the accuracy of the model. Second, the future typhoon and storm surge are estimated using the monthly mean value differences in SST, AAT, and RH from MIROC5 between 2011-2020 and 2091-2100 for the different scenarios. The & Ryota Nakamura characteristics of the simulated typhoon route and storm surge heights agree well with those of the best track data and field measurements. The numerical results of the future typhoon show that, if climate change is considered to only increase SST, its intensity and storm surge will be larger than under the present climate. The minimum sea-level pressure (hereafter, MSLP) of the future typhoon under scenario RCP 8.5 would be about 21 hPa lower and the storm surge 2.7 m higher than in the present climate. However, if SST, AAT, and RH are also taken into account, then the increase in typhoon intensity will not be as marked as if only SST is considered, with the MSLP under RCP 8.5 decreasing only by 13 hPa and the storm surge increasing by 0.7 m. The results of the present research thus suggest that while increases in SST can contribute to the intensification of future typhoons, increases in AAT and RH will somehow moderate this effect. Nevertheless, all scenarios considered point out to stronger typhoons and higher storm surges, clearly highlighting the perils posed by future climate change.
Typhoon Lionrock, also known as the national number 1610 in Japan, caused severe flooding in east Japan in August 28-31, 2016, leaving a death toll of 22. With a maximum sustained wind speed of ~ 220 km/h from the Joint Typhoon Warning Center's best track, Lionrock was classified as a category 4 hurricane in Saffir-Simpson Hurricane Wind Scale and as a typhoon in Japan Meteorological Agency's scale. Lionrock was among unique typhoons as it started its landfall from north of Japan. Here, we studied the characteristics of this typhoon through tide gauge data analysis, field surveys and numerical modeling. Tide gauge analysis showed that the surges generated by Lionrock were in the ranges of 15-55 cm with surge duration of 0.8-3.1 days. Our field surveys revealed that the damage to coastal communities/structures was moderate although it caused severe flooding inland. We measured a maximum coastal wave runup of 4.3 m in Iwaisaki. Such a runup was smaller than that generated by other category 4 typhoons hitting Japan in the past. Our numerical model was able to reproduce the storm surge generated by the 2016 Typhoon Lionrock. This validated numerical model can be used in the future for typhoon-hazard studies along the coast of northeastern Japan. Despite relatively small surge/wave runups in coastal areas, Lionrock's death toll was more than that of some other category 4 typhoons. We attribute this to various primary (e.g., flooding, surges, waves, strong winds) and secondary (e.g., landslides, coastal erosions, debris flows, wind-blown debris) mechanisms and their combinations and interactions that contribute to damage/death during a typhoon event.
Typhoon Faxai (T1915), which occurred in September 2019, was one of the strongest typhoons on record to make landfall in the Tokyo metropolitan area and it caused extensive damage along the coast in Tokyo Bay. Two intriguing phenomena are reported by a post-event survey, which motivated this study. The first is that although the storm impacted the whole bay, significant damage was concentrated in a small area near the Port of Yokohama. The second is about the direction of the hazardous waves, which came from both the northeast and the southeast. The underlying wave dynamics that lead to these events were unknown. Here, we elucidate characteristics of the waves incident to the Port of Yokohama that caused a concentration of severe damage, and we clarify the mechanism responsible for the two disparate wave directions observed. We found that the development of wind waves under slanting fetch conditions and the refraction of the swell by the Tokyo Submarine Canyon were key factors for generating unusual coastal wave spectra. Our results also demonstrate that the maximum wave power is a good indicator for the location of coastal damage.
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