Izuru Takayabu

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.

Over 5,000 Years of Ensemble Future Climate Simulations by 60-km Global and 20-km Regional Atmospheric Models

AbstractAn unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the a...

Validation of precipitation over Japan during 1985–2004 simulated by three regional climate models and two multi-model ensemble means

We dynamically downscaled Japanese reanalysis data (JRA-25) for 60 regions of Japan using three regional climate models (RCMs): the Non-Hydrostatic Regional Climate Model (NHRCM), modified RAMS version 4.3 (NRAMS), and modified Weather Research and Forecasting model (TWRF). We validated their simulations of the precipitation climatology and interannual variations of summer and winter precipitation. We also validated precipitation for two multi-model ensemble means: the arithmetic ensemble mean (AEM) and an ensemble mean weighted according to model reliability. In the 60 regions NRAMS simulated both the winter and summer climatological precipitation better than JRA-25, and NHRCM simulated the wintertime precipitation better than JRA-25. TWRF, however, overestimated precipitation in the 60 regions in both the winter and summer, and NHRCM overestimated precipitation in the summer. The three RCMs simulated interannual variations, particularly summer precipitation, better than JRA-25. AEM simulated both climatological precipitation and interannual variations during the two seasons more realistically than JRA-25 and the three RCMs overall, but the best RCM was often superior to the AEM result. In contrast, the weighted ensemble mean skills were usually superior to those of the best RCM. Thus, both RCMs and multi-model ensemble means, especially multi-model ensemble means weighted according to model reliability, are powerful tools for simulating seasonal and interannual variability of precipitation in Japan under the current climate.

Detecting latitudinal and altitudinal expansion of invasive bamboo Phyllostachys edulis and Phyllostachys bambusoides (Poaceae) in Japan to project potential habitats under 1.5°C–4.0°C global warming

Abstract Rapid expansion of exotic bamboos has lowered species diversity in Japans ecosystems by hampering native plant growth. The invasive potential of bamboo, facilitated by global warming, may also affect other countries with developing bamboo industries. We examined past (1975–1980) and recent (2012) distributions of major exotic bamboos (Phyllostachys edulis and P. bambusoides) in areas adjacent to 145 weather stations in central and northern Japan. Bamboo stands have been established at 17 sites along the latitudinal and altitudinal distributional limit during the last three decades. Ecological niche modeling indicated that temperature had a strong influence on bamboo distribution. Using mean annual temperature and sun radiation data, we reproduced bamboo distribution (accuracy = 0.93 and AUC (area under the receiver operating characteristic curve) = 0.92). These results infer that exotic bamboo distribution has shifted northward and upslope, in association with recent climate warming. Then, we simulated future climate data and projected the climate change impact on the potential habitat distribution of invasive bamboos under different temperature increases (i.e., 1.5°C, 2.0°C, 3.0°C, and 4.0°C) relative to the preindustrial period. Potential habitats in central and northern Japan were estimated to increase from 35% under the current climate (1980–2000) to 46%–48%, 51%–54%, 61%–67%, and 77%–83% under 1.5°C, 2.0°C, 3.0°C, and 4.0°C warming levels, respectively. These infer that the risk areas can increase by 1.3 times even under a 1.5°C scenario and expand by 2.3 times under a 4.0°C scenario. For sustainable ecosystem management, both mitigation and adaptation are necessary: bamboo planting must be carefully monitored in predicted potential habitats, which covers most of Japan.

A Multimodel Intercomparison of an Intense Typhoon in Future, Warmer Climates by Four 5-km-Mesh Models

AbstractIntense tropical cyclones (TCs) sometimes cause huge disasters, so it is imperative to explore the impacts of climate change on such TCs. Therefore, the authors conducted numerical simulations of the most destructive historical TC in Japanese history, Typhoon Vera (1959), in the current climate and a global warming climate. The authors used four nonhydrostatic models with a horizontal resolution of 5 km: the cloud-resolving storm simulator, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model, the Japan Meteorological Agency (JMA) operational nonhydrostatic mesoscale model, and the Weather Research and Forecasting Model. Initial and boundary conditions for the control simulation were provided by the Japanese 55-year Reanalysis dataset. Changes between the periods of 1979–2003 and 2075–99 were estimated from climate runs of a 20-km-mesh atmospheric general circulation model, and these changes were added to the initial and boundary conditions of...

An observational study of cyclogenesis in the lee of the Japan central mountains

SummaryAn observational study is conducted of the lee cyclogenesis that occurred on 11 December 1990 in the southeast region of the Japan central mountains (JCM). The area of the region, roughly defined by the 1000m above sea level is 250×250 km. The principal results are summarized as follows:i)The parent low, which triggered the lee cyclogenesis, was initiated by an upper-level vortex and accompanied by a low-level jet and surface cold front on the upstream side of the JCM. The system moved eastward along the northern edge of the JCM and dissipated.ii)The surface cold front approached the JCM, became blocked in the middle of the JCM, and stagnant for about three hours. South of the JCM, however, the cold front advanced eastward with no blocking. This resulted in the formation of a strong horizontal wind shear zone along the southeastern edge of the JCM, between the warmer air on the downstream side of the JCM and the colder air to the south. A shallow cyclonic vortex, confined to within 3 km above ground level was subsequently generated in the horizontal wind shear zone.iii)The vortex moved eastward along a meso-scale coastal warm front, which previously existed for more than ten hours over the Kanto Plain, since the morning of 11 December. The vortex coupled with the upper-level vortex when it moved over the warm sea area east of the Japanese Islands, and then rapidly developed (12hPa/12h).

Objective estimate of future climate analogues projected by an ensemble AGCM experiment under the SRES A1B scenario

Climate analogues (CAs), regions whose present climates are similar to the future climate of a target place, are identified to assess the effects of climate change towards the end of the 21st century. The location of CAs and their present climates yield information that may be used to mitigate the harmful impacts of climate change. Present (1979–2003) and future (2075–2099) climates are projected in an ensemble experiment using the atmospheric general circulation model of the Meteorological Research Institute in Japan. The ensemble members consist of combinations of four distributions of sea surface temperature, three convection schemes, and two initial conditions. The emission scenario for greenhouse gases is A1B of the Special Report on Emissions Scenarios. A new method to identify the location of CAs is introduced, in which the uncertainty in the climate projection is taken into account. CAs for all land regions of the world are presented and those of four capital cities are analyzed in detail. The CAs are generally distributed equator-ward from the target places, consistent with the global warming. It is also found that ensemble experiments that encompass the uncertainty of climate projections can yield robust results for the CA and lead to reliable assessments of climate change.

Physical Responses of Convective Heavy Rainfall to Future Warming Condition: Case Study of the Hiroshima Event

An extreme precipitation event happened at Hiroshima in 2014. Over 200 mm of total rainfall was observed on the night of August 19th, which caused floods and many landslides. The rainfall event was estimated to be a rare event happening once in approximately 30 years. The physical response of this event to the change of the future atmospheric condition, which includes a temperature increase on average and convective stability change, is investigated in the present study using a 27-member ensemble experiment and pseudo global warming downscaling method. The experiment is integrated using the Japan Meteorological Research Institute non-hydrostatic regional climate model. A very high-resolution horizontal grid, 500 m, is used to reproduce dense cumulonimbus cloud formation causing heavy rainfall in the model. The future climate condition determined by a higher greenhouse gas concentration is prescribed to the model, in which the surface air temperature globally averaged is 4 K warmer than that in the preindustrial era. The total amounts of precipitation around the Hiroshima area in the future experiments are closer to or slightly lower than in the current experiments in spite of the increase in water vapor due to theatmospheric warming. The effect of the water vapor increase on extreme precipitation is found to be canceled out by the suppression of convection due to the thermal stability enhancement. The fact that future extreme precipitation like the Hiroshima event is not intensified is in contrast to the well-known result that extreme rainfall tends to be intensified in the future. The results in the present study imply that the response of extreme precipitation to global warming differs for each rainfall phenomenon.

A GIS-Based Tool for Regional Adaptation Decision-Making for Depopulated Communities in Japan

Expert knowledge using high-resolution projection is a growing need and is particularly useful for local climate change adaptation. However, the inability to access and apply these scientifically-based climate data becomes a significant hurdle, especially in the poorest and most marginalized communities. Poor countries and depopulated communities in developed countries are more vulnerable to climate change because they tend to be in geographically weather-sensitive areas. This paper aims to: (1) develop an approach based on Geographic Information Systems (GIS) to cost-effectively and easily integrate observed and projected data into decision-making processes; (2) document how to adjust bias of projections, to provide accurate climate predictions for local decision makers; and (3) assist local decision makers in clarifying regional complex priorities for marginalized communities, with a wide array of adaptation options through efficient use of a GIS database. Kurihara (population 74,149; area 804.93 km2) in Miyagi Prefecture, Japan was chosen for a pilot study. The city comprises 10 depopulated communities within an active volcanic mountain and seismogenic area that is topographically complex, with the highest peak at 1,627.4 m. Post-disaster power shortages have renewed attention toward territorial planning and infrastructure, particularly in extreme climate regions. Our discussion focuses on how to transform the most recent regional climate projections (5 km resolution) into understandable and useful form for local policy makers to meet regional demands and to produce new forms of collective action via GIS. This method can be transferred to developing countries for potential climate change adaptation and mitigation plans.

An Application of a Physical Vegetation Model to Estimate Climate Change Impacts on Rice Leaf Wetness

AbstractA physical vegetation model [the Two-Layer Model (2LM)] was applied to estimate the climate change impacts on rice leaf wetness (LW) as a potential indicator of rice blast occurrence. Japan was used as an example. Dynamically downscaled data at 20-km-mesh resolution from three global climate models (CCSM4, MIROC5, and MRI-CGCM3) were utilized for present (1981–2000) and future (2081–2100) climates under the representative concentration pathway 4.5 scenario. To evaluate the performance of the 2LM, the LW and other meteorological variables were observed for 108 days during the summer of 2013 at three sites on the Pacific Ocean side of Japan. The derived correct estimation rate was 77.4%, which is similar to that observed in previous studies. Using the downscaled dataset, the changes in several precipitation indices were calculated. The regionally averaged ensemble mean precipitation increased by 6%, although large intermodel differences were found. By defining a wet day as any day in which the daily...