Typhoon Mireille (1991) caused devastation over Japan. Assessing the impacts of such an extreme typhoon under global warming is an important task to prevent and mitigate future natural disasters. This study investigated the influences of global warming on the strong winds of Typhoon Mireille by conducting pseudo-global warming (PGW) experiments with a regional model. Since significant damages to forest areas occurred in Kyushu and Tohoku, we compared the typhoon impacts in these two regions. It was demonstrated that on average the mean wind speeds induced by Typhoon Mireille become stronger in Kyushu and weaker in Tohoku under the PGW conditions than under the September 1991 conditions. The difference between the two regions in the future is due to the simulated typhoons under PGW being stronger at lower latitudes and weakening more rapidly at higher latitudes. Thus, the impacts of Typhoon Mireille under a warmed climate are considered to be more severe at a lower latitude and weaker at a higher latitude.
This study numerically investigates the influences of global warming on Typhoon Vera (1959) by conducting pseudo-global warming experiments. It was found that the intensity of Typhoon Vera will be stronger in warmed climate conditions than in the actual September 1959 condition not only at the time of the typhoon’s maturity but also at the time of the landfall. Sensitivity experiments indicate that this projected increase in the typhoon intensity is robust, by taking into consideration the effects of the increase in sea surface temperature and temperature lapse rate under global warming. The examination of rainfall characteristics over the Kiso River and the Yodo River basin demonstrated that the maximum accumulated rainfall and the maximum hourly rainfall at a certain location within the region are more intensified in the PGW conditions than in the 1959 condition at their worst levels. Robustness and uncertainty of the projected changes in the typhoon impacts are discussed.
This study uses an atmospheric general circulation model (AGCM), with a resolution of 60 km, to investigate the effect of high-horizontal-resolution SST data on simulations of elements of the East Asian summer monsoon (EASM), including the northwestern Pacific subtropical high (NWPSH) and tropical cyclone (TC) genesis. Plotting the result of the fine-resolution (60 km) minus coarse-resolution (300 km) SST AGCM runs shows a low-level anticyclonic anomaly (with suppressed convective activity) over the northwestern Pacific (NWP) following the onset of the NWP monsoon (July–September). In addition, TC frequency and mean TC intensity are controlled by the atmospheric circulation change that is related to the NWPSH. Changes in environmental parameters can partly explain these TC frequency and intensity changes. Based on the similarity between the realistic and idealized SST experiments, the cold SST anomaly around 10–15°N seems to play a key role in the low-level anticyclonic anomaly. Analysis of the ocean circulation and heat budget reveals that advection of cold water from the central Pacific by the westward-flowing North Equatorial Current (NEC) is important for the development of this cold SST anomaly.
Understanding future changes of ocean waves and storm surges is important for assessing and mitigating the impact of climate on coastal, marine and ocean environments and on engineering problems. This paper reviews the latest research results of climate change impacts on coastal hazards in Japan. First, future changes of wave climate and storm surges based on MRI-AGCM ensemble experiments are summarized. Second, the applications of coastal hazard projections to coastal structures and beach profiles are summarized as a series of climate impact assessment projects. There are clear increases in extreme values of wave heights and storm surges in the tropical cyclone dominant regions around the middle latitudes of the Western North Pacific including Japan. The influence of future climate change on caisson breakwaters is discussed considering sea level rise, extreme wave conditions and storm surges targeting the Pacific side of Japan.
The Pampanga River Basin in Philippines suffers from floods due to typhoons or monsoonal rainfall every year. Assessment of changes in flood risk due to global warming is, therefore, an important issue for this flood-vulnerable basin. We studied possible changes in rainfall features under present (1979–2003) and future (2075–2099) climates using dynamic downscaling of MRI-AGCM experiments. The GCM projections were downscaled into a finer resolution of 5 km for hydrological simulation (catchment size of 10,500 km2). The downscaled rainfall overestimated the number of weak rainfall events, which subsequently resulted in overestimation of monthly rainfall. Bias correction was carried out for downscaled rainfall with reference to raingauge rainfall to perform cumulative distribution mapping. The simulation results found that monthly rainfall would change slightly between present and future climate conditions, with extreme rainfall very likely to increase in the future. The annual maximum 48 h rainfall with a 50-year return period may increase from 320 mm under the present climate to 470 mm (MRI-AGCM 3.2S) or 530 mm (MRI-AGCM 3.2H) under the RCP8.5 future climate scenario. This increase in extreme rainfall in the future would have a significant impact on this vulnerable river basin.