Hirohiko Ishikawa

Kyoto University, Kioto, Kyōto, Japan

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Publications (42)60.88 Total impact

  • Source
    Yuichiro Oku, Jun Yoshino, Tetsuya Takemi, Hirohiko Ishikawa
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    ABSTRACT: Typhoon Talas (2011) caused extensive damage through landslides on the Kii Peninsula, Japan, in September 2011. The purpose of the present study is to quantitatively describe the potential for the occurrence of heavy rainfall-induced disasters if the typhoon track perturbs slightly or the typhoon intensifies. Regarding to the consideration of the track displacement of the typhoon, a procedure is proposed to generate different typhoon tracks perturbed from the original track of the typhoon. In this procedure, the position of a typhoon is artificially shifted at a certain time before landing in a physically consistent manner by applying potential vorticity inversion (PVI) methodology. After relocating the typhoon, the subsequent progress is simulated by a mesoscale meteorological model. Using the output, which consists of a set of realizations having different typhoon tracks, the worst-case scenario is discussed in terms of the soil water index (SWI) of the Kii Peninsula. The SWI is an indicator of the amount of water in soil that represents the hazard of landslide disasters. The maximum spatially averaged SWI is 1.10 times as large as that from the original typhoon track. Regarding the consideration of severer typhoon, the same method is used, but the intensity of the potential vorticity of a typhoon is artificially modified at the position instead of relocating potential vorticity to a different place. The maximum spatially averaged SWI is 1.28 times as large as that of the original typhoon intensity.
    Natural Hazards and Earth System Sciences. 10/2014; 14(10):2699-2709.
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    ABSTRACT: Radiation dose rates were evaluated in three areas neighboring a restricted area within a 20- to 50-km radius of the Fukushima Daiichi Nuclear Power Plant in August-September 2012 and projected to 2022 and 2062. Study participants wore personal dosimeters measuring external dose equivalents, almost entirely from deposited radionuclides (groundshine). External dose rate equivalents owing to the accident averaged 1.03, 2.75, and 1.66 mSv/y in the village of Kawauchi, the Tamano area of Soma, and the Haramachi area of Minamisoma, respectively. Internal dose rates estimated from dietary intake of radiocesium averaged 0.0058, 0.019, and 0.0088 mSv/y in Kawauchi, Tamano, and Haramachi, respectively. Dose rates from inhalation of resuspended radiocesium were lower than 0.001 mSv/y. In 2012, the average annual doses from radiocesium were close to the average background radiation exposure (2 mSv/y) in Japan. Accounting only for the physical decay of radiocesium, mean annual dose rates in 2022 were estimated as 0.31, 0.87, and 0.53 mSv/y in Kawauchi, Tamano, and Haramachi, respectively. The simple and conservative estimates are comparable with variations in the background dose, and unlikely to exceed the ordinary permissible dose rate (1 mSv/y) for the majority of the Fukushima population. Health risk assessment indicates that post-2012 doses will increase lifetime solid cancer, leukemia, and breast cancer incidences by 1.06%, 0.03% and 0.28% respectively, in Tamano. This assessment was derived from short-term observation with uncertainties and did not evaluate the first-year dose and radioiodine exposure. Nevertheless, this estimate provides perspective on the long-term radiation exposure levels in the three regions.
    Proceedings of the National Academy of Sciences 02/2014; · 9.81 Impact Factor
  • Weiqiang Ma, Yaoming Ma, Hirohiko Ishikawa
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    ABSTRACT: Evapotranspiration (ET) is a boundary condition for regional scale hydrological and climatological modeling. Spatial knowledge of land surface ET is of principal interest for environmental evaluation especially in semi-arid regions. The study used the Surface Energy Balance System (SEBS) model based on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing and field observations data that have been used and tested for deriving ET over the NamCo area in the Tibetan Plateau, located in the southwest of China. Two ASTER scenes were used for estimating the ET over the study area. To validate the proposed methodology, the ground-measured ET was compared to the ASTER derived ET values for the study area. The results show that the derived ET in different months over the study area is in good accordance with the in-situ data. The derived ET value over the study area is much closer to the field measurement; the RMSE is 0.7 mm/d. It is therefore concluded that the SEBS methodology is successful for the retrieval of ET using the ASTER and in-situ data over the study area.
    Atmospheric Research 01/2014; 138:91–97. · 2.20 Impact Factor
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    ABSTRACT: Analysis of (137)Cs trapped in biomass in highly contaminated zones is crucial in predicting the long-term fate of (137)Cs following the explosion at the Fukushima Daiichi Nuclear Power Plant. We surveyed forest 20 to 50 km from the plant in July and September 2011 to evaluate (137)Cs trapped in biomass within 20 km of the plant. We determined the ambient dose rate and collected forest soils and twigs at 150 sampling points. Removability from the canopy was evaluated by washing leaves and branches with water and organic solvents. The biomass of forest canopy was then calculated. (137)Cs fallout was simulated with an atmospheric transport model. The modeled dose rate agreed with observations (n = 24) (r = 0.62, p < 0.01). Washing experiments demonstrated that unremovable portions accounted for 53.9% ± 6.4% of (137)Cs trapped by deciduous canopy (n = 4) and 59.3% ± 13.8% of (137)Cs trapped by evergreen canopy (n = 10). In total, it was estimated that 74.5 × 10(12) Bq was trapped by canopy in the forest within the no-go zone, with 44.2 × 10(12) Bq allocated to unremovable portions, and that 0.86% of the total release was trapped in biomass as of September 2011.
    Environmental Science & Technology 07/2013; · 5.48 Impact Factor
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    ABSTRACT: The damage to society caused by tropical cyclones depends largely on the storm track relative to geography. A procedure is proposed to generate different typhoon tracks deviating from the original track of a given reference case. In this procedure, the position of a typhoon is artificially shifted at a certain time before landing in a physically consistent way by applying potential vorticity inversion methodology. After shifting the typhoon position, the subsequent progress is again simulated by a mesoscale weather model. The procedure is applied to a strong typhoon that emerged in a global warming experiment using an atmospheric general circulation model. Various realizations of typhoon landfall cases are generated. Using the output of a suite of realization of different tracks, the worst case scenario is discussed in terms of the river discharge in the Tone River basin, Japan. Copyright © 2013 John Wiley & Sons, Ltd.
    Hydrological Processes 01/2013; 27(23). · 2.50 Impact Factor
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    ABSTRACT: The idea of ground-based evapotranspiration (ET) is of the most interesting for land–atmosphere interactions, such as water-saving irrigation, the performance of irrigation systems, crop water deficit, drought mitigation strategies and accurate initialization of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent year's drought in Australia and concerns about climate change has prominent the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food security and production.This paper discusses the application of a Surface Energy Balance System (SEBS) model based on Landsat-5 TM data and field observations has been used and tested for deriving ET over Coleambally Irrigation Area (CIA), located in the southwest of NSW, Australia. 16 Landsat-5 TM scenes were selected covering the time period of 2009, 2010 and 2011 for estimating the actual ET in CIA. To do the validation the used methodology, the ground-measured ET was compared to the Landsat-5 TM retrieved actual ET results for CIA. The derived ET value over CIA is much closer to the field measurement. From the remote sensing results and observations, the root mean square error (RMSE) is 0.74 and the mean APD is 7.5%. The derived satellite remote sensing values belong to reasonable range.
    Atmospheric Environment 11/2012; 59:408–414. · 3.11 Impact Factor
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    ABSTRACT: This study aims to estimate the ecological exposure of adult residents of Fukushima Prefecture to ¹³⁴cesium (Cs) and ¹³⁷Cs through ingestion and inhalation between July 2 and July 8, 2011. Fifty-five sets of meals with tap water, each representing one person's daily intake, were purchased in local towns in Fukushima Prefecture. Locally produced cow's milk (21 samples) and vegetables (43 samples) were also purchased. In parallel, air sampling was conducted at 12 different sites using a high-volume sampler. Nineteen sets of control meals were collected in Kyoto in July 2011. ¹³⁴Cs and ¹³⁷Cs levels in the samples were measured using a germanium detector. Radioactivity was detected in 36 of the 55 sample meals from Fukushima, compared with one of 19 controls from Kyoto. The median estimated dose level (μSv/year) was 3.0, ranging from not detectable to 83.1. None of the cow's milk (21) or vegetable (49) samples showed levels of contamination above the current recommended limits (Bq/kg) of 200 for milk and 500 for vegetables. The total effective dose levels by inhalation were estimated to be <3 μSv/year at nine locations, but samples at three other locations close to the edge of the 20-km radius from the crippled nuclear power plant showed higher levels of contamination (μSv/year): 14.7 at Iitate, 76.9 at Namie, and 27.7 at Katsurao. Levels of exposure to ¹³⁴Cs and ¹³⁷Cs in Fukushima by ingestion and inhalation are discernible, but generally within recommended limits.
    Environmental Health and Preventive Medicine 11/2011; 17(4):292-8.
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    ABSTRACT: Environmental ecological modeling (EEM), which unifies models simulating transport of chemicals and exposure of humans to chemicals, was used to simulate long-term trends of female adult human blood lead levels (BLLs) and historical exposure to the atmospheric lead in four East Asian countries: Japan, Korea, China, and Vietnam. Anthropogenic lead emissions to the atmosphere in Vietnam were estimated from energy statistics to be 1931 t yr(-1). Calculated BLLs generally agreed with those observed in samples collected in these countries as the error factors were less than 2. The model results revealed that BLLs decreased significantly in Tokyo (by 58%) and Seoul (by 45%) in recent decades and confirmed the effects of efforts to reduce environmental lead in Japan and Korea. The model results also revealed that BLLs in Beijing did not decrease in this decade as much as in Tokyo and Seoul, despite the phasing out of leaded gasoline, and that the contribution from the atmospheric component was increasing (43% in 2009). Finally, we applied EEM to simulate BLLs of children in Hanoi. The probability of children having BLLs greater than 50 μg L(-1) was 7.5%, which was greater than those observed in developed countries.
    Environmental Science & Technology 02/2011; 45(7):2856-62. · 5.48 Impact Factor
  • Yuichiro Oku, Mizuo Kajino, Hirohiko Ishikawa
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    ABSTRACT: The algorithm used to retrieve the cloud effective particle radius from the 3.7 μm band was adapted to the corresponding channel of the Japanese Advanced Meteorological Imager (JAMI) flown on board the Multi-functional Transport Satellite (MTSAT) geostationary platform. Snapshot comparisons with spatially well-resolved retrievals from the MODerate resolution Imaging Spectrometer (MODIS) instruments flown on the Terra polar platforms show qualitative agreement with MTSAT retrievals. The results of analysing daytime variation from eastern Asia to the northwest Pacific Ocean show that, not only is the effective particle radius smaller in continental clouds than in maritime clouds, but the daytime amplitude of the effective particle radius is also greater in continental clouds than in maritime clouds, where the effective particle radius value is approximately constant.
    International Journal of Remote Sensing 10/2010; 31:5439-5447. · 1.36 Impact Factor
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    ABSTRACT: A publicly available atmospheric transport model, the Weather Research and Forecasting Chemistry Model ( http://ruc.noaa.gov/wrf/WG11/ ), was used to simulate atmospheric perfluorooctanoic acid (PFOA) and perfluorooctanoate (PFO) emitted from a point source in the Osaka urban area (also known as Keihanshin), Japan. The time period of the simulation was from 1983 to 2008. The modeled air concentrations were highly correlated (r = 0.91) with the observed air concentrations. Intake levels by inhalation of simulated air concentrations and through the gastrointestinal tract as estimated by the food duplicate method were input to a pharmacokinetic model of the human body to simulate serum concentrations of PFOA and PFO (PFO(A)). For validation of the atmospheric model, simulated values were compared with those observed in serum samples. The simulated values generally agreed with those observed in serum samples from residents of the Keihanshin area (r = 0.93). It was confirmed that the atmospheric model was generally capable of projecting features of atmospheric PFO(A) as well as serum concentrations of PFO(A) in this case. The results indicated a dominant contribution of the atmospheric component to serum PFO(A) in humans near the point source in the Keihanshin area. In 2008, that contribution was about 70%.
    Environmental Science & Technology 10/2010; 44(20):7852-7. · 5.48 Impact Factor
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    Yuichiro Oku, Hirohiko Ishikawa
    Advances in Geosciences, Volume 16: Atmospheric Science (AS). 05/2010;
  • Hydrological Research Letters. 01/2010; 4:1-5.
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    ABSTRACT: Parameterization of turbulent flux from bare-soil and undercanopy surfaces is imperative for modeling land–atmosphere interactions in arid and semiarid regions, where flux from the ground is dominant or comparable to canopy-sourced flux. This paper presents the major characteristics of turbulent flux transfers over seven bare-soil surfaces. These sites are located in arid, semiarid, and semihumid regions in Asia and represent a variety of conditions for aerodynamic roughness length (z 0m ; from 1 to 10 mm) and sensible heat flux (from 50 to 400 W m 2). For each site, parameter kB 1 [ln(z 0m /z 0h), where z 0h is the thermal roughness length] exhibits clear diurnal variations with higher values during the day and lower values at night. Mean values of z 0h for the individual sites do not change significantly with z 0m , resulting in kB 1 increasing with z 0m , and thus the momentum transfer coefficient increases faster than the heat transfer coefficient with z 0m . The term kB 1 often becomes negative at night for relatively smooth surfaces (z 0m 1 mm), indicating that the widely accepted excess resistance for heat transfer can be negative, which cannot be explained by current theories for aerodynamically rough surfaces. Last, several kB 1 schemes are evaluated using the same datasets. The results indicate that a scheme that can reproduce the diurnal variation of kB 1 generally performs better than schemes that cannot.
    Journal of Applied Meteorology and Climatology 03/2008; 47:276-290. · 2.02 Impact Factor
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    ABSTRACT: In this study, a parameterization method based on Landsat-7 Enhanced Thematic Mapper (ETM) data and field observations is presented and tested for deriving the regional land surface variables, vegetation variables and land surface heat fluxes over a heterogeneous landscape. As a case study, the method and two Landsat-7 ETM images are applied to the Jiddah area of Saudi Arabia. The regional distribution maps of surface reflectance, normalized difference vegetation index, modified soil adjusted vegetation index (MSAVI), vegetation coverage, leaf area index, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux have been determined over the Jiddah area. The derived results have been validated by using the ‘ground truth’. The results show that the more reasonable regional distributions of land surface variables (surface reflectance, surface temperature), vegetation variables (MSAVI and vegetation coverage), net radiation, soil heat flux and sensible heat flux can be obtained by using the method proposed in this study. Further improvement of the method is also discussed. Copyright © 2006 John Wiley & Sons, Ltd.
    Hydrological Processes 06/2007; 21(14):1892 - 1900. · 2.50 Impact Factor
  • Yuichiro Oku, Hirohiko Ishikawa, Zhongbo Su
    Journal of Applied Meteorology and Climatology 01/2007; 46(2):183-. · 2.02 Impact Factor
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    01/2007;
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    ABSTRACT: Low-frequency microwave brightness temperature is strongly affected by near-surface soil moisture; therefore, it can be assimilated into a land surface model to improve modeling of soil moisture and the surface energy budget. This study presents a new variational land system used to assimilate AMSR-E brightness temperature of vertical polarization of 6.9 GHz and 18.7 GHz. The system consists of a land surface model (LSM) used to calculate surface fluxes and soil moisture, a radiative transfer model (RTM) to estimate the microwave brightness temperature, and an optimization scheme to search for optimal values of soil moisture by minimizing the difference between modeled and observed brightness temperature. The LSM is an improved simple biosphere model for sparse vegetation modeling and the RTM is a Q-h model that can account for the effects of surface roughness and vegetation. Several parameters in the LSM and RTM can significantly affect the outputs of the land data assimilation system but their values are either highly variable or unavailable. To solve this problem, we developed a dual-pass assimilation technique. Pass 1 inversely estimates the optimal values of the model parameters with long-term (∼months) forcing data and brightness temperature data, while Pass 2 estimates the near-surface soil moisture in a daily assimilation cycle. This system is driven by well-established reanalysis data and global data sets of leaf area index, precipitation, and surface radiation, and was tested at a CEOP (Coordinate Enhanced Observing Period) reference site on the Tibetan Plateau. The system not only detected the effect of precipitation events that were missing in the forcing data, but also led to a significant improvement in modeling of the surface energy budget.
    Journal of the Meteorological Society of Japan 01/2007; 85A:229-242. · 0.80 Impact Factor
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    ABSTRACT: Similarity between temperature and water vapour was investigated in the Fourier domain by using their coherency spectra, defined as the correlation coefficient between their Fourier modes, and the relative efficiency of their vertical transport. The class-averaged values of these indices were computed from the turbulence measurements over sparse grasslands on the Tibetan plateau during the intensive observations of GEWEX (Global Energy and Water Experiment) Asian Monsoon Experiment (GAME). It was found that the energy-containing eddies at scales up to 100z (z being height) are characterised by well-maintained similarity between these scalars. The scalars are highly correlated with each other, and their transport efficiencies are almost equal within this scale range. In contrast, similarity was not always maintained at scales larger than 1000z. Detailed analyses showed that this breakdown of similarity occurs occasionally or sporadically, suggesting that it is caused by events whose average return period is not much smaller than the current averaging time, i.e. 30min. We speculate that entrainment of drier and warmer air at the top of the atmospheric boundary layer caused the scalar dissimilarity at this scale range.
    Boundary-Layer Meteorology 12/2006; 122(1):85-103. · 2.29 Impact Factor
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    ABSTRACT: Sensible and latent heat fluxes from the plateau surface are of great importance in the Asian monsoon system. Since the plateau occupies a wide area and the environmental conditions are severe to perform surface observation, the satellite remote sensing is inevitably a practical tool to estimate these fluxes from whole plateau surface. The in situ flux estimation is, however, necessary as a ground truth for the satellite remote sensing. It also gives scientific information in constructing land surface-atmosphere model, which shares an important part of data assimilation system using satellite data. There are several different approaches in estimating in situ heat fluxes. The simplest method uses operational observation and experimental parameters, and it gives steady continuous estimation. The more sophisticated Bowen ratio or profile observation gives the more precise information. The estimation with turbulence measurement together with the measurement of radiation and soil heat fluxes give detailed description of land surface-atmosphere interaction suitable to model development. Since 1998, a combination of these methods has been applied to the Tibetan plateau. The efforts of these in situ flux observation and the current understandings are summarized in this presentation.
    Advances in Earth Science. 12/2006; 21(12):1237-1243.
  • Advances in Earth Sciences. 12/2006; 21:2006.

Publication Stats

328 Citations
60.88 Total Impact Points

Institutions

  • 2002–2014
    • Kyoto University
      • • Disaster Prevention Research Institute
      • • Department of Health and Environmental Sciences
      Kioto, Kyōto, Japan
  • 2004–2013
    • National Research Institute for Earth Science and Disaster Prevention
      Ibaragi, Ōsaka, Japan