Currently, desertification has become a realistic problem around Chinese Loess Plateau thereby the suitable preventive measures must be urgently adopted. Planting is expected as an effective measure for preventing land desertification, and the available water resource is essential for this planting project. Since the mean annual precipitation is only 400 mm with non-uniform occurrence, estimation of annual available water becomes quite difficult. In the current study, we carried out the field survey on a basin named Liudaogou which has representative topographical and hydrological features of the upper Loess Plateau region. By considering the relation between occurrence of the surface flow and the corresponding rainfall, we evaluated some characteristics of the surface flow and the basic infiltration property of the topsoil. By using the relevant result, we performed the runoff calculation by the conventional kinematic wave model and summarized some runoff characteristics of the upstream region in Loess Plateau.
Hydropower has been accepted as a clean source of energy that relies on proven technology. There are many estimates on global theoretical hydropower potential published in technical literatures, but the results have been found inconsistent. This study presents a 0.5-degree grid based assessment of global theoretical hydropower potential using recent data for global runoff produced by Global Soil Wetness Project, an international land surface modeling project. The gross theoretical hydropower potential for many countries was found larger than the previous estimates. This difference has mainly attributed to the need for a clear view on the theoretical hydropower potential, which would serve as a base to find the technical and economical potential to promote hydro electricity mainly in terms of small hydro in developing countries.
From November 2006 to June 2007 a field experiment ‘Tanashi Experiment’ was conducted in a farm of the University of Tokyo, Japan. The scientific objectives are presented in this paper and the corresponding experiment set-up is described. The influences of soil moisture and vegetation layer on the brightness of various frequencies are analyzed. The sensitivity of higher frequencies on the soil moisture changing is identified. The TB of all frequencies and polarization is found to be saturated and reach same values when vegetation water content larger than 4kg/m2. A Land Data Assimilation System developed by the University of Tokyo (LDAS-UT) is validated by using data obtained from this experiment. And one important merit of LDAS-UT, parameter optimization, is verified through the comparison of optimized parameters with the in situ observed ones. The difference between the optimized parameters and the observed ‘real’ ones reveals the potential source of uncertainty in the system due to the limitation of current Radiative Transfer Model (RTM) and Land Surface Scheme (LSS).
One of the destruction mechanisms of historical earthen walls in Ajina Tepa site, Tajikistan is the salt crystallization. Halite, calcite and gypsum are found as the major salts crystallized on the historical walls. Because the rate of crystallization is thought to be a function of evaporation, the evaporation from four earthen walls was measured by using a newly developed portable evaporation meter. Before the measurement, the accuracy of the evaporation meter was carefully studied under the no-wind and the wind conditions in laboratory and field tests in Japan. The effect of average wind velocity on the evaporation measurement was also evaluated before the measurement. It was found that the evaporation rate is big at the foot of the historical wall and is decreasing with height. This feature implies that moisture is mainly supplied from ground and the protection cover of which height is at least 1m is needed to prevent the destruction of historical wall due to the salt crystallization.
High concentration of fluoride ion up to 12mg/l is observed in deep groundwater at the Tono area, Japan. A simple but general method to evaluate the occurrence of high fluoride ion concentration in groundwater has reported in this study. Our method based on the water-rock interaction test using different sizes of granite powders sampled from a boring core drilled at the site. Results indicated that, the weathering of granitic rock might be one of the key components for changing the fluoride ion concentrations. And also the increase of the reaction time led to enhance leaching of the fluoride ion from granite. To deduce the contribution of the co-existence of the chemical parameters, which affected on the change in the fluoride ion concentration, a stochastic model was developed. This model shows significant evaluation of the water-rock interaction test with the chemical data of a low Na- (Ca) -Cl water-type. Results from our stochastic model indicated that the approximation reaction time of the water-rock in the granitic groundwater was about 300 days at this region.
This paper provided reasonable results of groundwater storage estimation and its distribution on each aquifer in Uzbekistan. The largest aquifer was Kyzylkum. There were very rare publication and discussion paper on the groundwater storage in arid region. Then the results were useful finding to support the decision maker and researchers who were interested in this subject. In this study, the estimation of groundwater storage using GIS techniques and utilization of borehole data was proposed. The result showed that groundwater storage in Uzbekistan was about 15.5 BCM (billion cubic meters), while in Kyzylkum aquifer was about 6.8 BCM. Compared with the result from Central Asia Water Info, field survey and roundtable discussion Uzbekistan on August 2007, the results was verified, reliable and acceptable.
This paper investigates the development and application of a daily optimization (DO) model to the short-term operation of the water supply system of Matsuyama, Japan. The main objective of the procedure is to seek the best allocations of water that minimizes the squared deviations between releases and target demands. The daily precipitation for one week ahead is assumed to be deterministic since meteorological short-range forecasts are generally available. The groundwater balance is modeled by Multiple Linear Regression (MLR) and short-term predictions of reservoir inflows are obtained based on the daily precipitations by means of Artificial Neural Networks (ANNs) . System operations using fictitious simulation and the DO model under perfect short-term forecast of inflows are used for comparison. The results of the DO procedure using ANN-based inflow predictions are shown to be equivalent to those obtained by DO under perfect short-term forecast of inflows and superior to the ones found by simulation.
This paper proposes a lumping method of a distributed rainfall-sediment-runoff model. The lumping method is divided into two parts: lumping of the kinematic wave distributed rainfall-runoff model, and lumping of the distributed sediment transportation model that takes into account for erosion and deposition by raindrop and overland flow. A kinematic wave distributed rainfall-runoff model is lumped based on the assumption of steady state conditions. Soil detachment and deposition from an entire catchment are simulated by the balance between the current sediment storage and the maximum sediment storage, which is estimated from a distributed rainfall-sediment-runoff model as a function of total surface water storage of the lumped rainfall-runoff model. The proposed lumping method is examined by comparing water and sediment discharges simulated by the distributed and the lumped rainfallsediment-runoff models in the Lesti River Basin, Indonesia.
Distributed hydrological models are capable of predicting the internal behavior at any point within a study basin. However, most cases, models are calibrated only at the catchment outlet and prediction accuracy at ungauged points inside is not assured. In this study, we investigate the capability of a physically based distributed hydrological model for predicting internal behavior by calibrating only using discharge observations at the basin outlet. It is found that the prediction ability for internal discharges is different depending on the initial condition; and especially the prediction accuracy of the floods with dry initial condition is low. This is due to a spatially uniform parameter setting for satisfying the calibration at the catchment outlet. Incorporating spatial heterogeneity of the parameter value for easily generating surface flow along the channel network improves the discharge prediction inside for different initial conditions.
A raster-based stormwater simulation model is formulated and applied in this study. The proposed model employs the raster-based distributed approach for describing the surface rainfall runoff process. Surface runoff is generated from each grid cell and then is routed to the inlets/manholes of drainage channel network by using 2-D diffusion wave. The hydraulic process in the drainage channel network is performed by using the EXTRAN module, a component of the Storm Water Management Model (SWMM) . The input flow rate at inlets is calculated by using weir equation. The surcharge outflow rate from the drainage channels is calculated by using Preissman slot concept. The proposed model is successfully applied to reproduce the heavy flood event on August 4, 1998 in Kamedagou basin, Niigata Prefecture, Japan. Further more, the well-calibrated stormwater simulation model is utilized to inundation mitigation planning in the study area.
Flood hazard is one of the most harmful disasters in the world, and it is significant to obtain information on flood characteristics for hazard mitigation as well as vulnerability assessment. This paper develops a model for simulating flood inundation integrating with rainfall-runoff processes. The model is designed to operate with the Shuttle Radar Topography Mission (SRTM) DEM data and other globally open data sets, based on the simplified process representation capable of simulating flood inundation. It consists of a one-dimensional diffusion wave representation for channel flow and a two-dimensional diffusion wave approximation of overland flow solved using an explicit finite difference scheme. In the model, exchange of flows between river channel and overland surface is calculated through Manning's formula in response to the relative water surface elevation. Simulated results in the Maruyama River basin show an acceptable agreement with the observed flooded area. Hence the flood vulnerable area is able to be identified and delineated. This research is a fundamental step to assess flood hazard vulnerability at any global catchments.
This study focuses on a prediction of the largest ever flood, which caused by Typhoon Rusa in 2002 at the GamCheon Basin, Korea, with a distributed hydrologic model. Using hydrologic events data earlier than the typhoon flood, the model was calibrated with the SCE optimization algorithm under various conditions, such as different event size and duration, integrating evaporation information and adopting additional model parameters for distributed land use. As more hydrologic data (evaporation and land use) integrating, the model shows improved simulation behavior for long-term events. However, parameter sets calibrated with short term events provides stable and efficient prediction on the Rusa flood event.
This paper aims to raise the growing importance of predictive uncertainty evaluation in distributed modeling. The ideas are illustrated by applying a particular rainfall-runoff model in four catchments with different characteristics. Sensitivity analysis and parameter identifiability, as complimentary uncertainty measures allowed us to individually evaluate the suitability of model components. The Sobol implementation is affected by the sample size and the correlation degree among parameters, observed after the total sum of individual variance contributions exceeded a theoretical total variance of 1.0, in magnitudes that varied from 5% in dry season to 60% in wet season, turning more difficult straightforward interpretations. Topographic index was used to judge the distributed performance of the model, adequately describing patterns of total discharge in homogeneous catchments with slopes ranging from 10% to 30%, and failing in less homogeneous catchments with low slope landscape.
A natural rainfall-runoff process is conceptualized by means of mathematical form reflecting a physical law and hydrologist's perception and it is typically calibrated and verified based on streamflow data, the commonly used catchment response. The streamflow data is obviously required, but is not sufficient to identify a conceptual parameter of a hydrologic model since numerous parameter combinations can often result in quite similar numerical values in terms of objective function and even indistinguishable simulated hydrographs. One of the efficient techniques to resolve this impasse is a combination of the model with streamflow data augmented by other kinds of hydrological information relevant to the prediction. In this study, internal dynamic response of catchment, spatiotemporally separated components of hydrograph, to the various mimic parameter sets is presented. It is concluded that all of simulations based on plausible parameter combinations sampled by using deterministic and stochastic automatic optimization algorithms, are performed equally well in terms of both model performance measure and visual comparison between observed and simulated hydrograph while internal behaviors of catchment show totally different aspects. The spatiotemporal information presented here can be utilized as one of the complementary constraints capable of filtering out non-physical parameter set (s) .
This study developed a regional Intensity?Duration?Frequency (IDF) relationship for ungauged locations based on the scaling theory. The scaling properties of extreme rainfall are examined to establish scaling relationship behaviors of statistical moments over different durations. The results show that a rainfall property in time does follow a simple scaling process. A scale invariance concept is explored for disaggregation (or downscaling) of rainfall intensity from low to high resolution and is applied to the derivation of scaling IDF curves. These curves are developed for ungauged sites based on scaling of the Extreme Value type 1 (EV1) or Gumbel probability distributions. The spatial distribution maps of three parameters: the scaling exponent and two statistical parameters are constructed. By using these maps, the IDF relationships are deduced from only daily rainfall with the scaling approach, which shows good agreements in comparison with the IDF curves obtained from traditional techniques.
Regional flood frequency analysis which is applicable for estimating design flood at both gauged and ungaged sites needs grouping of river basins into hydrological homogeneous regions. Specific flood, timing of flood events and spatial location are significant in reflecting physiogrpahy and climate of any river basins. These three physiographic/climatic characteristics of 46 independent Nepalese river basins have been used successfully to delineate the homogeneous regions. This study uses a clustering algorithm as a starting point for partitioning the independent catchments. The regions thus formed are subsequently revised to improve the regional homogeneity after performing the L-moment based homogeneity test. Spatial proximity consideration has been used to delineate region for mountainous dependent river basins whereas subjective considerations have been made to delineate region for river basins of alluvial plain region.
In previous investigations on the Neyman-Scott clustered Poisson rectangular pulse rainfall model (NSM), model parameters were often estimated using rainfall moments, covariances, correlations, and dry moments while model performance was often assessed through the accuracy of extreme values. No former contribution included extreme value information in improving the parameter search. This was the motivation of the authors in finding a link between the scaling apparent in the historical rainfall maxima and the NSM parameters. The normalized variance or Fano factor of the Peaks Over Threshold (POT) rainfall process was adopted to define this link. In general, the results obtained from this approach showed acceptable performance with minor limitations.
In the case study presented here, the calibrated parameters of a Conceptual Rainfall-Runoff (CRR) model could not be uniquely identified. Moreover, the Posterior Probability distribution (PPD) of Model Parameters varied among basin depending upon the basin attributes and data aspects. So the assessment of parameter uncertainty of CRR models should become the integral part of regionalisation. For that reason, we proposed a regionalisation scheme which instead of regionalizing the single best value of model parameters, regionalizes the PPD of model parameters. Subsequently the number of model parameters are sampled from the estimated distribution and fed into the model. Regionalisation of PPD addresses the effect of model parameter uncertainty in the result of regionalisation. The uncertainties in model prediction quantified from proposed methods closely followed the prediction uncertainties quantified from PPD of model parameters conditioned on observation in the presented case study.
Nagoya city is one of the largest city located at central zone of Japan. Main rivers such as Shounai River, Shin River, Hori River, and Yada River etc. are passes through densely populated city area and terminated into Pacific Ocean. A synthetic urban inundation model is applied for the simulation of inundation in the Nagoya city in various cases such as sea level rise by 0.5m, 0.95m, 1.5m, 2.0m with the design rainfall of 10 years return period. From this study, it is found that if the sea level rises more than 1m then severe inundation occurs in the densely populated city area between the Hori River and Nakagawa canal. Furthermore, the effect of sea level rise on the sewerage system is examined.
The flood inundation model for highly urbanized area is different with general flood inundation due to the increasing of the complexity of nature and internal boundaries. As consequences, the flow is complex and requires a stable numerical model to solve it. In this paper, the flood inundation model for highly urbanized area is presented. The explicit MacCormack scheme was used to solve the flow equations. The artificial viscosity scheme was added to reduce the numerical oscillations. The model was first verified by the benchmark tests. Here, the simulated results were compared with the analytical solutions. The good performance of the model was achieved. The model was applied to simulate and to evaluate the past flood inundation in 2004, Aioi area of Kofu, Yamanashi. Compared with the observed data, the model was satisfied to be applied in highly urbanized area. It could be a useful tool for the water authority and the local government to design the countermeasures, to identify the inundation processes and to determine the potential inundation hazard map.
As a meshfree particle method, the Moving Particle Semi-implicit (MPS) method is ideally suited for simulating the complicated behaviour of water surface with fragmentation. In this paper, the original formulations of MPS method are revisited from the view point of momentum conservation. Modifications and corrections are made to ensure the momentum conservation in a particle-based calculation of viscous incompressible free-surface flows. The excellent performance of Corrected MPS (CMPS) method in the exact (and nearly exact) conservation of linear (and angular) momentum is shown by a simple numerical test. The CMPS method is then applied to the simulation of wave breaking and post-breaking. Refined simulation of a solitary plunging breaker and resultant splash-up is demonstrated through comparisons with experiment. A tensor-type strain-based viscosity is also proposed for further enhanced CMPS reproduction of splash-up.
This paper proposes a new method for continuous measurement of pollutant load in rivers without much cost. The basic idea is making the most of “empirical correlations which exist in the target” in order to relate what we can measure to what we want to know. In a field experiment presented here, signals from two types of optical sensors were used to estimate the loads of chemical oxygen demand (COD), total nitrogen (T-N) and total phosphorus (T-P), and artificial neural network (ANN) models were trained to fix “the empirical correlations” among them. The field data were collected in seven rivers located in the watershed of Lake Kasumigaura. The experimental results showed that the three items of water quality were stably estimated with good accuracy for rather long time without too much training data.
Effectiveness of two types of densely grown coastal vegetation, namely Pandanus odoratissimus and Casuarina equisetifolia were investigated with different ground slopes, against a tsunami event in 2-D numerical simulation. Dimensions of vegetation patches and gap between them were changed rationally in order to represent possible vegetation shapes available on hinterland. Both vegetations showed similar trend of hydraulic properties variations. It was observed that reduction of maximum current velocity is higher than the reduction of maximum water depth behind vegetation patch. Horizontal run-up length is reduced with the patch size increases for very mild ground slope, but when slope becomes steep, gravity effect is dominant than vegetation effect on run-up length. Relatively big patches with narrow gap are identified as destructive forms. In fact maximum current velocity is increased at gap-outlet, gap-inlet and middle of the gap when tsunami flows landward, towards offshore and in both directions respectively compared to the bare land.
Debris flow is a phenomenon that high-density water with mud and big gravel flows down along a stream at high speed. Because of its high density and speed, it has huge destruction power. Thus damages by debris flows are very severe and sometimes tragic. A check dam is commonly used for preventing the sediment disaster due to debris flow by storing the harmful sediment discharge and has various types. Numerical simulations and experiments have been carried out to investigate the mechanism of debris-flow deposition process upstream of a check dam, and flushing out of deposited sediment due to erosion process by a normal scale flood flow. The simulations and experiments have been performed using closed type and grid type check dams. The simulated results agree well with the experimental results. From the results, it is shown that the grid type check dam can keep their sediment trapping capacity more effectively than the closed type check dam.
Morphological and hydrological conditions are main factors to influence the probability and magnitude of sediment disasters. This study tried to develop a method for hazard mapping of sediment disasters from these two aspects. Aerial photographs and historical debris flow susceptibility analysis were used to distinguish the potential debris flow torrents, digital terrain model was used to make the topographic data, and hydrologic frequency analysis was used to evaluate the probable discharges extreme value from two survey stations in a study watershed in Taiwan. Finally, the results made in the first part were input in the Flo-2D software model to simulate the deposited area for each torrent. To create a hazard map, the results from simulation were divided into several levels in terms of danger based on landslide intensity.
Formation and failure of landslide dam are one of the significant natural hazards in the mountainous area all over the world. In the event of catastrophic failure of landslide dam, we have to predict resulting outflow hydrograph. It will serve as an upstream boundary condition for subsequent flood routing to predict flood hazard in the downstream. Most of the existing models are applicable to overtopping failure of landslide dam. In this study an attempt has been made to incorporate integration of three separate models to predict the outflow hydrograph resulted from failure of landslide dam by overtopping and sudden sliding through flume experiments and numerical simulations. The main advantage of an integrated model is that it can detect failure mode due to either overtopping or sliding based on initial and boundary conditions. The proposed model is tested for three different experimental cases of landslide dam failure due to overtopping and sliding and reasonably reproduced the resulting hydrograph.
Sediment system in watershed is not only sediment yield but also including sediment transportation along the rivers. In this study, the Geographic Information System (GIS) combined with sediment yield model can be enhancing the evaluation of soil erosion estimation. Surface erosion on Managawa river basin is computed with the Modified Universal Soil Loss Equation (MUSLE) and it is verified to reflect the hydrological processes be able to estimate soil losses. In the sediment transport routing module, total load equation is applied to carry sediment from soil surface erosion to deposit in Managawa dam. According to annual accumulation sediment volume data in Managawa reservoir during 1981-2003, the establish model and simulation results are satisfy. The efficiency of the Modified Universal Equation with sediment routing in rivers is more than the simple Modified Universal Equation.
Formation of the initial bedforms, known as sand-wavelets, developing from a flat erodible bed in hydrodynamically smooth flow has been studied numerically. The computational model consists of hydrodynamic and sediment transport equations. The unsteady hydrodynamic equations are solved by Large-Eddy-Simulation (LES) and Immersed-Boundary-Method (IBM) on a non-bodyfitted grid. Dynamics of individual grains are neglected and only bedload is considered, as calculated from Van Rijn's equation (1984, Journal of Hydraulic Engineering, Vol. 110) . Two-dimensional (2D) bed evolution is coupled with the above 3-dimensional (3D) hydrodynamic equations. The computed wavelength agrees with linear stability analysis and with experimental data in the literature. The length of the sand-wavelets is observed to correspond to the disturbance region of bed shear stress caused by discontinuities on the bed surface, as postulated by Yalin (1977, Mechanics of Sediment Transport, Pergamon press) .
The objective of this study was to obtain a better understanding of high turbidity generation in the upstream region of the Hitotsuse River watershed, by focusing on analyzing the turbidity response to discharge in the river stream. This study revealed that there were 3 types of sources of turbid water in the study area, namely: Type 1 (Collapsed of mountainside), Type 2 (Outflow of collapsed soil), and Type 3 (Waterside erosion) . This study proposed the Turbidity Discharge Ratio as means for detecting the problem of turbid water generation. The results showed that the Turbidity Discharge Ratio was fluctuate during 1994-2003. Turbidity Discharge Ratio was very high, slightly after the occurrence of heavy rainfall triggered by a typhoon. This study clarified that the Turbidity Discharge Ratio tended to decrease due to the lesser amounts of fine particles transported to the river and the cumulative discharge about 200x103m3/s is required to reduce the Turbidity Discharge Ratio below 1.
This paper presents the results obtained from the studies on turbulent flow and bed deformation around groins with experimental and numerical methods. Two impermeable or permeable groins were positioned on the left side of the model channel. The velocity distributions around the groins were measured under non-submerged conditions. In the case with impermeable groins, the local scour hole around the upstream groin resulted deeper than that of the case with permeable ones. A 3D numerical model based on unstructured meshes was developed. The numerical results for velocity distributions have been compared with those of the experimental measurements and show good agreement with the experimental data.
Flood event has obvious and long-lasting impacts on channel morphologies, posing high risks of damage and/or failure of river restoration projects. This study evaluates the impacts of flood event on the channel morphologies around typical river restoration structures and provides possible management alternatives for a real restoration project. Both laboratorial experiments and numerical simulations have been carried out. The experiments are based on a large-scale physical model, being able to resolve local flow patterns and morphological variations with a high accuracy. The numerical model is formulated on unstructured meshes, allowing the exact representation of complex geometries and boundaries. It is shown that the numerical results are reasonably consistent with those of the experimental measurements. The numerical model might make a powerful tool and the results of this study would be of excellent references for future engineering designs and post-project assessments in the river restoration.
Detection of spatial representativeness of rainfall is important for the prevention of disaster. This study analyzed the spatial representativeness of rainfall based on observed data at the railway observational stations and the meteorological stations of Japan Meteorological Agency in Kanto Plain and the mountains region of Koshin-etsu. The results can be summarized as follows: The 95th percentile of the 1-hour (24-hour) precipitation ratio between two stations is about 1.5 (1.2) at the distance of two stations is one kilometer. The high spatial representativeness area of ordinary 1-hour (24-hour) precipitation is about five (ten) kilometers, and one of local 1-hour (24-hour) precipitation is about two (five) kilometers. The spatial representativeness is higher in the plain than in the mountainous region. The orographic effects become larger when the distance of two stations exceeds two kilometers.
This paperdescribes contribution of strongwind events onDissolved oxygen (DO) concentrations inTokyo Bay by statistical analysis. Tokyo Bay is a typical enclosed bay in Japanwhose water quality has been deteriorated. For example, the occurrence of anoxic water in the bay head adjacent to the seabed is frequent. Since estuarine circulation dominates DO concentration and a strong wind event is revealed toenhance recoveringprocesses of DO concentration, thisstudy aims to understandstatistical characteristics of strong windeventson DO concentration in Tokyo Bay. Strong windperiod, interval and intensity were tested as indicator of strong wind events' statistics. As a result, pdf analysishas potential in the evaluationof the recovery processes ofDO concentration around the headofTokyo Bay. Strongwind events werealso revealed to appearfrom May to August dominantly.
There is a possibility that the population of extreme precipitation has been changed by a climate change. Therefore it is necessary to estimate the probable hydrological amount which can correspond to the population change using an unsteady frequency analysis. In this paper, each precipitation data set of 22 meteorological observatories in Hokkaido is divided into 2 partial-duration time series of sample size, n1 and n2 (n1≥7, n2≥30, N=n1+n2), to detect a mean and a variance jump. Then, T-year probable hydrological amount using n2 data which is significant for the jump is estimated to compare with the predetermined probable hydrological amount for complete-duration series of sample size, N. Consequently, we clarify that T-year probable hydrological amount of the annual maximum daily rainfall and the annual maximum number of days with continuous non-rainfall need to be renewed by 0.1-49% increase for 12 observatories and 2-14% increase for 5 observatories respectively.
The source area of acidic oxide in Japan is likely to differ with the season. It is considered that acidic oxide in the East Japan is mainly brought by advection from the East-Asia continent in winter. In summer, it may be brought by advection from Yokkaichi seaside industrial area in the central part of Japan. In this study, transportation process of the acidic oxide in the East Japan was investigated by an advection and dispersion model (HYSPLLIT4) . The advection process of acidic oxide in each season also was investigated through trajectory analysis and through numerical transport simulations. The acidity of precipitation tends to be higher as a whole in summer than in winter in the East Japan, while the concentration of acid ion increases in winter in part of the northern Kanto region. The results of the trajectory analysis and transport simulations shows that the source area of sulfur dioxide transported to the East Japan in winter is likely to be the northern part of China.
A non-stationary time series is composed of the trend and some jumps by the change of a mean value and a variance. There is no study example which hasdealt with the power of test fora jump of variance in a hydrological time series. In this paper, the Monte Carlo simulations are applied to compare the power of the statistical tests: Student's t test, F test, Mann-Whitney test and bootstrap test to assess the significance of jumps to affect the mean value and the variance of a time series with Normal, Logarithm Normal and General Extreme Value distributions. And also, the outliers in the annual maximum daily rainfall (MDR) and annual maximum non-rainfall days (NRD) data of each 22 meteorological observatories in Hokkaido are detected at Tomakomai and Hiroo for MDR data, and at Esashi for NRD data, respectively. Then the normalized conditionsto change these three outliers into normal values are introduced by using a numerical simulation.
Extreme environmental events such as rainstorms give severe consequences to human society. Magnitude evaluation of an extreme event for a given return period is an important step in planning of flood prevention facilities. The estimation of the spatial distribution of magnitude is difficult because extreme events are rare and the data record is often short. Regionalization resolves this problem by “trading space for time”; data from several sites are used in estimating event frequencies at any one site. Applying regional frequency analysis, regression analysis and kriging method to Miyagi prefecture, we have obtained the estimates and the accuracy for probable rainfall and discussed incorporation of orographic effects.
In the past, the snow algorithm for Microwave Scanning Radiometer - Earth Observing System (AMSR-E) was developed by Tsutsui, Koike et al (2005, 2007) . This algorithm was improved for Special Sensor Microwave Imager (SSM/I) in this paper. It is for investigating long-term snow depth before Aqua is launched (2002) . Furthermore, snow depth in the Northern Hemisphere of the period from 1988 to 1999 was estimated from SSM/I satellite data by this algorithm, and the estimation result was argued.
This paper describes the influence of the change of land-use in Kanto Plane on urban climate in summer. Numerical simulations of urban climate from Aug. 10 to 11, 2007 were carried out by using WRF meteorological model under the conditions of Present, Edo-Era, and Future. From the computations, following conclusions are obtained. (1) The daytime temperature in Present Case is 2 to 3 °C higher than that of Edo-Era due to sea breeze and sensitive heat, and the nighttime temperature is also 4 °C higher than that of Edo-Era due to sensitive heat. (2) The daytime temperature in Future Case is 7 °C higher than that of Present Case in reclamation area due to reclamation land. However, the nighttime temperature in Future Case is a little bit lower than that of Present Case.
A numerical simulation was carried out to investigate the characteristics of sea breeze intrusion on the Fukuoka Metropolitan area by using ARPS and the results were compared with the field data of sea breeze obtained in August 2, 2003. The sea breeze front runs parallel to the costal line at the beginning of the sea breeze intrusion, but as it goes into the inland, the two-dimensional front becomes wavy and breaks. The sea breeze consists of the tail of about 600 m thickness and the head 1000 m and above high. The head is accompanied with a pair of upward and downward currents that reach to about 2000 m height.
The region of local high temperature is formed in the suburb of the south part of Fukuoka metropolitan area. The data were obtained in the summer seasons of 2003 and 2004. They were analyzed to reveal the weather conditions in the case where the local high temperature appeared. It is seen when the flux of solar radiation was large and the wind speed was not so large. The difference between the averaged temperature over the whole observation region and that over the local high temperature region increases with the increase of the flux of solar radiation. The local high temperature seems to be strongly dependent on the local geophysical features.
Mechanisms of the development of local circulation and convective updraft around Tonle Sap Lake were examined by using a non-hydrostatic model (ARPS) coupled with a land surface scheme (SiB2) . Two atmospherically calm periods with little influence of the monsoon were selected as this research targets: one was in April with around the minimum lake area and the other in October with the almost maximum. The results of the numerical simulation show clear local circulations induced by the lake-land contrast and the mountain topography. Convective updraft was formed during daytime at the lakeshore due to the lake breeze both in April and October. During nighttime, a lined up convective system was formed only in October when the difference of air-mass density between over land and lake was larger. These convective activities are considered to correspond to the rainfall events in the southwest region in the evening in October and on the lake during nighttime in April.
The present study investigated the relationship between the mean and instantaneous characteristics of turbulence within the atmospheric surface layer over urban like roughness. To make it, we compared the horizontal distribution of the turbulent fluctuations and the turbulent statistics, which are derived from the same data obtained in the facility of comprehensive outdoor scale model for urban climate (COSMO) . It is known that the turbulent motion within the atmospheric surface layer is composed of active and inactive eddies. The active eddy is originated from the surface under neutral stratification and relevant to the turbulent transport process. The inactive eddy is attributed the mixing in the atmospheric boundary layer and irrelevant to the turbulent transport process. To evaluate the characteristics of active turbulence which reflects the characteristics of roughness, we decomposed the turbulent fluctuation into the active and inactive components. This analysis revealed that the streaky structure observed in COSMO is attributed to the active turbulence.
Particle image velocimetry (PIV) was applied to the turbulent flow within and above an outdoor urban scale model. The setup of the PIV system and the preliminary results were presented. Two dimensional turbulent flow fields in a vertical cross section of street canyon (3 x 3 m) were measured continuously for 60 min; the spatial and temporal resolutions were 5cm and 1/30 sec, respectively. The mean wind vector and turbulent statistics were successfully obtained. Also the PIV results were validated with measurements of ultrasonic anemometer which is conventional instrument for the investigation of atmospheric turbulence. Most of them showed good agreements within the error of 10% although the data aquisition ratio was still low.
Fukuoka University constructed a football field using a new-type artificial turf with improved soil on May 2007 in order to mitigate urban heat-island phenomenon and urban flooding. To clarify hydrometeorological environment in the football field, we installed the hydro-meteorological observation system inside the football field. Furthermore, potential evaporation from the football field was measured using the model experiment. As a result of the hydro-meteorological observation, meteorological environment over the artificial turf was analogous with environment over natural grass. In the nighttime, air temperature over the artificial turf was about 5 degree Celsius lower than in urban area. Moreover, runoff ratio of the field was 12%-14.5% and a lag time between peaks of a flood and a maximum rainfall was 4hours. As a result of the evaporation model experiment, evaporation rate from our proposed artificial turf system was slowly and continuously during 10 days. The new-type football field contributes to the mitigation of urban heat environment and urban flooding.
A unit effluent load has been widely used for evaluation of pollutant loads flowing into eutrophic lakes and inner bays, although the applicability of the unit effluent load for non-point sources has been severely limited. This study presents newly an unsteady unit effluent load for roof-deposit load, one of non-point sources in urban area, using its association with dry fallout. For this purpose, we have conducted a long-term, continuous monitoring of the amount of sediments and nutrients on the roof (SSroof, TNroof and TProof) during two years. The measured results indicate the good correlations not only between SSroof and dry fallout, but also between SSroof and TNroof (TProof) . The unsteady effluent load is described with these relations and measured SPM. This method was applied to evaluate the temporal variations of roof-deposit loads, showing the fundamental validity of the present method.
We carry out the microclimate field observation collaborated closely with local residents in the downtown of Tokyo in order to study the effect of watering on urban climatic environment. Local residents sprinkled recycled water which was rainfall and/or bath water in summer. Then we measured air temperature, humidity, solar radiation, aerosol number, wind velocity and wind direction all the day. We could observe atmospheric phenomena before/after watering. The following conclusions were obtained: 1) Air temperature at almost all observation stations were started to decrease immediately after watering started. Area-averaged air temperature declined by 0.5 deg. C. After Watering, it took an average time of 60 minitues to relapse to the air temperature immediately before the sprinkling. 2) Surface temperature of roadway decreased from 50 deg. C to 40 deg. C compared between before and after Watering. Assuming the surface of roadway could be black body, long-wave radiation declined from 620 W/m^2 to 510 W/m^2 compared between before and after watering. Heat environment mitigation action by watering could be divided into “fall of air temperature” and “restraint of radiation”.
To investigate the impact of the actual sea surface temperature (SST) of Tokyo Bay on urban air temperature, an observation network was constructed. SST had been measured at 14 observation sites, such as the lighted buoy in Tokyo Bay since November 2006 to September 2007, and urban air temperature was simulated using the numerical modeling system, WRF, in which SST obtained from this observation was used. In this study, the following results are obtained. (1) From observational study, spatial distribution of air temperature is similar to that of SST, and air temperature over Tokyo Bay is considerably affected by air advection from the coastal land area. (2) Actual SST of Tokyo Bay has significant seasonal and diurnal variation compared with outer SST. (3) Air temperature at Tokyo increases about 0.1°C in summer if the outer SST is replaced with observed SST in Tokyo Bay in the numerical simulation.
Using oxygen isotopic ratio and humidity, a new simple method of measurement for an evaporation rate in a lake is proposed. The oxygen isotopic ratio of the Inawashiro Lake is thought to have increased from -10.3‰ to -9.3‰ estimating from river flow rates and lake and river oxygen isotopic ratios. As a result of some evaporation experiments, the relation between evaporation ratio, initial oxygen isotopic ratio and humid was analyzed and then the evaporation ratio in the Inawashiro Lake was estimated 5.6 % from the relation and oxygen isotopic ratios. The evaporation in the Inawashiro Lake is calculated about 560 mm per year from 5.6 % evaporation ratio, lake inflow and lake area and is in agreement with that estimated by Jacob equation.
Field measurements of momentum and CO2 fluxes over the ocean surface were made at a sea observation tower by means of the eddy correlation and inertial dissipation methods. Under ideal surface layer conditions, the good agreement may be seen between the fluxes obtained from both methods. The combined use allows us to identify efficiently reliable flux data. The values of these fluxes are found to vary depending on wave-field conditions, i. e., the presence of swell. On the ocean surface, the change in the air density becomes so relatively large that corrections concerning sensible and latent heat fluxes, i. e., the Webb corrections, should be made for evaluating the flux of CO2. The present data show that the corrections are very important to estimate accurately the total CO2 flux across the air-sea interface.