The Seta River is the only one natural outlet river of Lake Biwa. This paper examines the relationship between water level of Lake Biwa and discharge of the Seta River in historical years. Since there are no gauged discharge data in historical years, water level data are transformed into differences of outflow from inflow (Q_out-Q_in) using the relationship between water level and storage volume (H-V relation) of Lake Biwa. The results indicate that flow capacity of the Seta River was expanded after the dregging in Tempo years (1831-1833), and that there were no notable changes in flow capacity during Meiji Period (1874-1899).

View full abstract

Recent days, many people are interested in natural environment of rivers. The Ministry of Construction have been attempting to preserve or to restore natural envioronment of rivers, since 1990 in Japan. In Tohoku district, river planning has been implemented to restore biotope in the Iwaki river which flows in Tugaru area at Aomori Pref. It gives educational chances to children and people who wantto meet living things in the river field. Considering the circumstances, this paper discriminates the following: preserving area, restoring area, watching living things area and digging to create shallow water area to expect to restore biotope.

View full abstract

Nagaoka city area in an alluvial fan is dangerous in flood control, because the Shinano River flows fast, meanders and attacks the area. Safety of levees is a serious problem. After the alignment of low water channel was examined in a hydraulic model experiment as well as a training levee, a low water revetment has been executed the work since 1975. About 25 years have passed, the site observationresults were compared with the hydraulic model experiment results about changes of a riverbed and reduction of flow attacking effect. The effect of training levee, which is main concern of this planning, is evaluated by numerical simulation.

View full abstract

Water resources in the lower Mekong river basin as an international river, was evaluated using a conceptual analysis method based on water balance. GIS prepareddata sets of elevation, land use and slope data to understand the ratio of.land use in the area. A conceptual area was introduced for easy understanding. It wascovered with only three categories, which are forest, urban and cultivated regions. Water balance equation involving rainfall, evapotranspiration, infiltration, storage and runoff was calculated for water demand for people. As the results, the number of drought months will increase as cultivated area will increase. Especially, serious seasons are dry season and the rice-planting season. It was alsounderstood that population in the area would be limited by water supply for people. Japanese climate condition was also used to compare with the Mekong region. Although this model is simple, the obtained results show us the possibility of the future problems.

View full abstract

It is necessary to improve basin residents' interest and stimulate public participation in activity for preservation of water environment. The purpose of this study is to construct a methodology for stimulating public participation in various activities for preservation of water environment. This paper analyzes questionnaire to residents in the Sendai River basin and members of some Non-Profit Organizations. The results of analysis show new knowledge as follows: 1) main factors affecting interest, 2) structure of participation in activity, 3) 5 styles ofparticipation in activity, and 4) relationship between experience and a new interest in the river. Finally, a methodology called “Circle Approach of Public Participation” is constructed on new knowledge.

View full abstract

In rcccnt years, many local governments have composed flood hazard maps and officially distributed them to the residents.
This study surveys flood hazard maps composed in 57 local governments as of March, 2000. The purpose of the investigation is to promote local government to establish their own hazard maps and tomake the maps more effective to users, focusing on the contents of the maps, themethod of official announcement, subsequent evaluation, and so on.

View full abstract

A first priority on crisis management during a natural disaster is to minimize or to mitigate casualties. Therefore refuge information should be transmitted to inhabitants effectively so as to help them understand the situation exactly and to select an evacuation behavior. In order to attain these aims, refuge information has to be transmitted in such a way that the inhabitants can easily understand the words, contents, context of the sentences and a sense of the impending crisis from the sender. In this study, we did questionnaire investigation in Kiryu City, Gunma Prefecture as an example to examine refuge information transmission to promote resident's refuge. Then we considered the viewpoints of timing, mediaand content of refuge information transmission with the assumption that a flood disaster happens.

View full abstract

Small mountainous river basins have a strong possibility that heavy rainfall will cause river flood disaster and sediment disaster. In such areas, the local severe rain occurs in the narrow range and the water level of the river comes up rapidly because of the steep slope. So it is important that inhabitants have the discernment for judgment of the risk of a heavy-rain calamity and refuge at just the appropriate time based on the circumference situation. In this study, we grasp the actual condition of the inhabitants' cognition involving heavy-rainfall hazards in small mountainous basins based on the investigation carried out in Kiryu City, Gunma Prefecture, from the viewpoint of the understanding of the information about the heavy-rainfall hazard on a flood hazard map.

View full abstract

Nitrate nitrogen transport with denitrifying conditions in unsaturated Ando soilwas investigated. At first, the experiment of nitrate nitrogen transport was carried out in the artificial rain using the vertical column filled up with Ando soil. Simulated rainfall dissolving nitrate nitrogen and organic carbon was sprayed on the top of column and nitrate nitrogenc oncentrations of soil solution at some depth points were measured. From the experimentalr esults, denitrificationp rocessw as detected. Next, the experimentarl esultsw ere simulatedu sing one-dimensionanl umerical model, which described denitrification process based on Monodtype kinetics. Simulated results of denitrification process had good agreements with experimental results. Moreover, it was distinct that the activity of denitrifing bacteria from soil surface up to the 10 cm depth point was the highest in the Ando soil column.

View full abstract

Owing to overflows from combined sewer pipe systems, water quality of receiving waters, including urban rivers, has become worse year by year. Appropriate countermeasures that can mitigate the overflows, therefore, must be developed promptly. The authors have investigated a distributed simulation model of water qualityand stormwater runoff in urban sewer pipe systems. First, a surface routing model of stormwater and pollutants, which is a sub-model of the distributed model, is proposed. Second, the routing model is applied to a roof and a road surface of Matsuyama city and the applicability of the model is investigated on the basis of the comparisons of observed and simulated hydrographs.

View full abstract

For effective water environmental management, knowledge on the pollutant runoff mechanism from non-point sources is very important especially under the rain condition. The runoff rate of not only the stormwater but pollutant loads distributed over the watersheds hould be dealt with physically-basedr ainfall-runoffr elationship.
This paper has conducted field observation about the nitrogenous pollutant runoff in the Honmyo river, an A-class river in Nagasaki. The observation results have been discussed from several viewpoints, based on a mathematical model. Finally, developed model has been proven to be available for estimating the diffuse pollution from the watershed.

View full abstract

In Hokkaido, we have often experienced ground surface freezing during the winter. The Tomisato dam experiment basin was set up to clarify the effects of frozen soil on the snowmelt runoff. It is possible in snowmelt season to occur the overland flow at the hillslopes because of reducing infiltration capacity of ground surface by soil freezing. By analyzing observed data, it was pointed out that the swell of long wavelength of hydrograph occurred in the early snowmelt season.
To make clear the effects of frozen soil on the snowmelt runoff, we reconstruct 4×3 zoned tank model, which can consider the spatially distributed frost depth and snow depth at this site, by including the frost dept prediction model. By multiple regression analysis, the frost depth is good relationship between freezing index, snow depth and melting index, and the max value of frost depthis dependent upon the accumulate rainfall at autumn season. As a result, it shows that this improvement is effective to estimate the snowmelt runoff in the coldand snowy region with the frozen soil.

View full abstract

The current paper investigates how storm and long term runoff characteristics changed with the growth and increase of vegetation in the Ashio basin. Ashio basinwas damaged by wood fire and smoke pollution resulting from copper refining. However, tree planting and sand control works have been carried out and vegetation is recovering.
In order to study the change of runoff characteristics due tothe recovery and growth of vegetation, we installed rainfall and water gauges at5 points in the Ashio basin. For the sake of accuracy, beside our observations, we also considered in our study, results of water stage observations made by the Ministry of Construction and by the Forestry Agency. As a results peak discharge, total outflow of flood, as well as outflow of long term have been decreasing due to vegetation increase and recovering.

View full abstract

This paper deals with a method for estimating the main model parameters of SWMM, i.e. the imperviousness ratio: F, the equivalent roughness coefficient of impervious area: N_i and the depression storage of impervious area: d_pi at a small urban basin.
First, by using the single basin model, we optimized the values of the model parameters. The optimum values of F are distributed in the wide range, and they are lager than the value of the imperviousness ratio obtained from the land-utilization map. The optimum values of N_i have also the wide range of distribution according to the hyetograph patterns. On the other hand, the optimum values of d_pi are nearly constantfor various rainfall events. Second, by using the separated basin model, we examined the optimum values of N_i. The results of runoff simulations showed that the value of N_i optimized for the heavy rainfall was well applicable to runoff forecasting for the other rainfalls.

View full abstract

The steep-slope topographic condition makes Japan to face the problems of high sediment production and yield in many areas. The problems are much severe in comparison with the other part of the world, but slightly less than the East and Southeast Asia and South American areas. However, with many reservoirs which relatively small in size, the sediment depositions in the catchments create very serious problems.
In order to understand the sediment production and yields in the catchments scale, the USLE, the most widely used of Sediment Estimation Model, was applied in the catchments of Arakawa, Daimon, and Hirose reservoirs in the Fuji River Basin. The result indicated that if parameters are properly selected to reflect the regional conditions, the USLE is adequately applicable for estimating long-term mean annual sediment production in the area.
The results couldbe useful to understand the spatial variation in sediment production that is required for erosion and sediment yield reduction management on the basin. While for the short-term or annual sediment deposition calculation, some problems were encountered where the methodology could not explain the observed accumulated sediment in the reservoirs.

View full abstract

This paper deals with the flood routing in river networks where the solution cannot be obtained from hydrologic routing methods. An improvement for dynamic unsteady one-dimensional (1-D) flow simulation based on Preissmann implicit finite difference scheme with simultaneous solution is developed. The river networks aredescribed by a set of basic river reaches between two nodes. A procedure for automatically creating the order for controlling double-sweep is established. It then is applied for flood routing in the river network of a part of the Red river basin, Vietnam. From the results, the improvement is expected as an effective treatment for dynamic flood routing in river networks of dendritic type.

View full abstract

The objective of this study is to develop a distributed hydrologic model using SMPT (Soil Moisture Parameter Tank model) which was presented by Ando et. al.(1982). The watershed basin is divided a grid cell of 50m in which direct runoff, evaporation, and ground water runoff was calculated. The model is applied to simulate water cycle in the Azuma Upper Experimental basin (1.81km²) witha time step of a day. The model parameter is calibrated through the compare the simulated river discharge, groundwater levels and with the observed value.

View full abstract

A grid-based hydrological cycle analysis model was developed and applied to Ebi river. This model consists of three components; surface and near-surface section, river section, and groundwater section. In surface and near-surface section, infiltration, percolation, interflow, and return flow were computed solving one-dimensional Richard's equation in each grid cells. Kinematic wave model was applied to river flow computation. Interaction between river and groundwater was represented by Darcy's flow through riverbed material. Quasi-three dimensional Darcy's flow model was adopted beneath the surface and near-surface section. Model calibration is carried out with several river and groundwater observation station data. The results agreed with the observation of river flow rate as well as groundwater level.

View full abstract

A distributed hydrological model-WEP (Water and Energy transfer Process) model is improved at first by adding overland flow and storm-water detention pond's components, as well as changing the kinematic wave method into the dynamic wave method for the flow routing of main rivers to consider tidal effects. The modified model is then utilized to evaluate the effects of storm-water detention ponds and infiltration trenches in the Ebi river watershed with a grid size of 50m and atime step of 10 minutes. The simulation of the Shibayama-Danchi No.1 storm-waterdetention pond at the upstream of Miyamae tributary is performed by adopting a design rainfall of one day duration and 50mm/hour peak. Four cases, namely, with pond, with trench, with pond and trench and without pond and trench are studied at 4 sites, namely, pond outlet, Miyamae river downstream, Ebi river middle-stream and Ebi river mouth. Through comparing the hydrographs at the 4 sites in the 4 cases, it is found that the storm-water detention pond plays a much bigger role than infiltration trenches in flood peak reduction in the upstream reach, whereas infiltration trenches distributed over the watershed play a dominant role inthe downstream reach. Therefore, the joint implementation of storm-water detention ponds and infiltration trenches may be necessary for effective flood damage mitigation in a whole watershed.

View full abstract

Today, we can get high quality information about spatial distribution of rainfall observed by radar on real time. In order to make effective use of such a spatial rainfall information, and to improve the flood forecasting accuracy for dam operation, we developed a real time dam inflow prediction system based on distributed rainfall-runoff model. In our system, channel flow is calculated by using the integrated kinematic wave model for channel networks, and the state of channel flow is updated with Kalman filter. Simulations are carried out with dam inflow data and precipitation data observed by rain gauges, and it was confirmed thatthe prediction system performs well.

View full abstract

A simplified model for subsurface flow computation is developed by splitting thecontinuity equation on the flow into vertical and horizontal directions based onthe evaluation that the major part of the lateral flow occurs in the saturated zone. This model is combined with the surface flow model on the channel network and applied to the Abukuma River watershed of 5, 400km² area to reproduce the flood in 1998. Discharge hydrograph computed by this model shows good agreement withthe observed one and remarkable improvement from the surface flow model.

View full abstract

A macro scale grid based distributed hydrological model is applied to the Huaihe River basin in China (140, 000km²). In the modeling, a watershed basinis subdivided into grid boxes according to a grid system of a meso-scale atmospheric model to incorporate atmospheric model outputs. Model parameters are determined by using the data sets obtained in the Shigan River basin during the intensive observation period in 1998. Some runoff simulations showed that channel routing has dominant effect on a simulation of river discharge for a large river basin.

View full abstract

In continental and global scale modelling of land surface processes, stream flow, lateral movement of channel water within a channel network is an important component. It is an indispensable component in a fully coupled atmosphere-ocean-land general circulation models (GCMs). The aim of this study is to develop a synthetic runoff routing model for continental-scale river basins. Considering the resolution of typical GCMs, the model resolution is set to 1.0°. This model is designed to accept runoff generated in grid cells within a river basin, and route them to assigned points through a channel network. In this routing model, three routing schemes, Miller's scheme, kinematic wave model and multi-step multi-reachMuskingum-Cunge scheme are implemented. By applying this routing model to theChangjiang and Mississippi river basin, intercomparison of these three routing schemes is carried out.

View full abstract

In hydro-environmental simulation, DEM based stream network plays a very important role. The artificial stream network is widely used since it is essential to build a distributed hydrologic model reflecting topographic and other land surface heterogeneity. However, to increase its reliability and accuracy, some problems need to be further elaborated. One of them is the choice of drainage directionassignment rule. Among the various exiting methods, the steepest slope approach and the lowest elevation method were compared in theory and practices. It was found that the different direction assignment rules yield quite different hydrographs and that the rules need a major attention in grid DEM based hydrological study. In addition, practical ways of handling deserts, inland rivers and to enlarge DEM grid size are presented in the case of the Yellow River of China.

View full abstract

Distributed runoff models have been becoming powerful for describing the naturalrunoff processes. Such kind of model should reflect topographical features of a catchment. Then, it is necessary to examine about the possibility of aggregationas the catchment model. The purpose of this study is to investigate the effect of catchment scale of the element on runoff response characteristics. Runoff simulations in the conditions of the overland flow and the interflow by using two kinds of different mesh sizes of digital elevation model in the Hayakawa River, central Japan, were carried out. Then the concentration times of these runoffs were discussed. The result is as follows; 1) the concentration time depends on the mesh scale, 2) the influence of aggregation caused a difference in case of computation, and 3) the problem is solved by using a model parameter that gets equivalent average concentration time.

View full abstract

Spatial resolution of topographic information gives a great influence to distributed runoff analysis. The objective of this study is to evaluate the effects of spatial resolution of DEM (Digital Elevation Model) on flood analysis with 1-D main flow channel. Kinematic wave propagation is simulated through real and imaginary river channel data sets having various resolutions. This study reveals that (1) Low resolution of DEM shortens delayed time of peak discharge, because smallhorizontal curves of river channel are omitted and channel elements become shorter;(2) Vertical curves in channel profile have also significant influence to discharge. An accuracy of discharge analysis greatly depends on the correlation between spatial resolution and wavelength of topographic vertical curve; and (3) Sufficient resolution is about 1/50 of the wavelength.

View full abstract

The objective of this study is to develop an algorithm for quantitative estimation of snow parameter distributions using Synthetic Aperture Radar (SAR) data anda numerical scattering model that includes the Integral Equation Method (IEM) model and first-order radiative transfer solution. Simultaneous RADARSAT SAR observations were carried out during the winter seasons of 1996 and 1998. The study area is a part of the Hokuriku District of Japan that is well known for having ofwet snow with a complicated layer structure from the beginning of the winter season. We compared the results of simulated backscattering coefficients with the ground-truth data and observed backscattering coefficients. Since the agreement was good, we demonstrated the possibility of estimating roughness distributions of soil surface using images acquired just before the snowfall, assuming that thesoil conditions did not change during a winter season. Furthermore, we estimatedthe distributions of snow depth and roughness using images after a snowfall and estimated soil roughness distributions.

View full abstract

To understand the spatial and temporal distribution of water storage in reservoirs is important for water resources management as well as for studying water cycle on the global. In this study, a method for estimating water storage in a reservoir is proposed based on satellite observations and digital elevation model. The relationship between area of water surface (A) and volume of water storage (V) is calculated from digital elevation model, and modeled as V=a A^b. Using this A-V relation, the water surface measured from satellite images can be translated into the volume of water storage.
The proposed algorithm is applied to Yagisawa-reservoir, which is located in upper reach of the Tone river basin in Japan. Although estimated water storage does not yet satisfactorily agrees with the observed, potential of storage volume estimation by this method is well demonstrated.

View full abstract

The impacts of Southern Oscillation (SO) on climate are widespread and extend far beyond the tropical Pacific, a phenomenon known as teleconnection. The oscillation can be characterized by Southern Oscillation Index (SOI) which is derived from values of the monthly mean sea level pressure difference between Tahiti and Darwin, Australia. Its best-known extreme is the El Nifio event.
In this study, general statistical characteristics of SOI and the data from which it is derived (i.e. mean sea level pressure data at Tahiti and Darwin) are presented as guidance when using SOI for other analyses.The characteristics include the availability of the barometric pressure data, statistics of monthly pressure data, correlation of SO intensity, frequency analysis of SOI by magnitude and by month (January- December), duration properties of SOI by run analysis.

View full abstract

Among many technologies for decontaminating soil and groundwater, electrokinetic remediation is gaining increasing attention. Before implementing it in the actual field, numerical simulations are indispensable to optimize running conditions. A few models have been developed already. These models have not included dissolution of soil particles, and adsorption phenomena etc. Therefore, the purpose of our research is to develop a new model for electroremediation, which will be able to be used under actual soil condition. We developed an ion diffusion-migration code to simulate the behavior of dissolved ions under the condition of electrical potential gradient. A test for a case of instantaneously injected NaCl point source into the water solution gave results comparable to the analytical solution. This code was employed for the simulation of electromigration-diffusion transport of chemical species under electrical potential gradient in the NaCl solution. The simulation shows process that the dissolved ions migrate toward opposite charged electrode and accumulate with time. The formation process of pH jump is also shown in the numerical result.

View full abstract

Depth-area-duration (DAD) analysis has been used in a lot of papers about temporal and spatial distribution of heavy rainfall for long years. In this paper, similar analytical method is used in order to clarify characteristics of temporal and spatial distribution of scarce precipitation that is main cause of drought. First, normalized precipitation by mean annual rainfall is defined. Next, depth-duration curve that is linear approximation is obtained. By this approximation and the result of depth-area analysis, DAD curve that represents fairly the data is obtained. Furthermore, the seriousness of drought is evaluated statistically by the similar method as drought-duration curve method.

View full abstract

This paper exmamines the usefulness of a probability distribution with lower-and upper-bounds for small samples with a size of 20 to 30. Small samples for more water periods and less water periods are extracted from a long-term (10, 000) series of lognormal variates generated by the Monte Carlo technique. The accuracy of T-year event estimates is assessed when the probability distribution with upper-bound is applied to these small samples. The results here recommend that for such samples that include large events the incorporation of upper-bound gives better T-year event estimates. It avoids overestimation of T-year quantiles. However, the use of the probability distribution with no upper bound is recommended for such small samples that only small events are included in the sample. The use of the probability distribution with upper bound for such samples tends to underestimate the T-year events.

View full abstract

In hydrologic frequency analysis, a variety of probability distribution functions, such as the gamma, log-normal, extreme-value, and log-gamma, are often examined whether they are appropriate to the flood data or not by using some hypothesis testing methods, because the properties of the flood data are not well understood even now. In order to find a property of the flood data, we can use another method: using the more general probability distribution function which includes many types of probability distributions used for hydrological statistics. The 4-parameter extended generalized gamma distribution function is one of such distribution functions. Two types of the extended distributions are proposed. The parameter estimation method is also introduced.

View full abstract

Recently, a lot of researches on predicting climatic change have been conducted, and the effects of climatic change on agriculture have been estimated from the viewpoint of agricultural meteorology. Quantitative evaluation of this effect is not, however, easy, since improvement of yields are related to multiple factors, including plant breeding and improvement of irrigation technology. This paper considers the relationship between precipitation and agricultural characteristics, and more specifically, an index that indicates the effect of drought on the yield. First, drought and pluvial years are defined here by the amount of precipitation, and the characteristics of both are discussed. Next, duration of drought is defined in three ways is considered. It could be concluded that duration of drought is an important index for predicting agricultural yields.

View full abstract

Flood frequency analysis uses two types of extreme-value series: the annual maximum series (AMS) and the partial duration series (PDS) or the peaks-over-threshold (POT) data. Though the AMS has a few disadvantages, it has been used in many countries without identifying which method is more appropriate for analyzing flood peaks or extreme rainfalls. This paper discusses which method should be used for analyzing flood peaks. Samples are 105 continuous time series of discharge in A-class rivers in Japan. The Gumbel distribution and the GEV distribution are used for the AMS, the exponential distribution and the generalized Pareto (GP) distribution for the PDS. Consequently, the PDS is recommended through the comparison of the AMS and the PDS in terms of shape parameter, quantile estimates, SLSC goodness of fit and quantile stability.

View full abstract

An application of wavelet analysis is done with the total monthly rainfall data of Matsuyama city, in order to analyze the rainfall variability observed in such an area. Besides the rainfall variability analysis, the main frequency components in the time series are studied by the global wavelet spectrum, revealing that the monthly rainfall in Matsuyama city is composed mainly by an annual frequency. Thus, the modulation in the 8-16-month band is examined by an average of all scales between 8 and 16 months, giving a measure of the average monthly variance versus time, where the periods with low or high variance could be identified.

View full abstract

A new equipment with an open chamber for measuring evaporation rate from the soil surface is described in this paper. The chamber differs from commonly used chambers due to the fact that it is completely open at the entrance. The chamber covers a ground area of 0.6 m² and has a volume of 0.3m³. A suction arrangement has been used in passing air through the system and the ventilation rate can be regulated up to a maximum value of 90 m³/h. The evaporation rate measured by the equipment showed good agreement with the evaporation rate measured by a balance both in the laboratory and the field. The net solar radiation was reduced by about 6% due to the chamber. The soil moistureunder the chamber showed good agreement with the simulated values as well as with the soil moisture measured outside the chamber. The pressure difference within and outside the chamber was found to be negligible. The open chamber system minimizes its influence on the natural environment and thus gives better measurements.

View full abstract

Turbulent flow past a complex topography, represented by an idealized two-dimenional hill with gentle slope is simulated by LES technique. Flow Reynolds number is moderately high to exhibit difficulties in the mostly sought boundary conditions in LES of practical flows. Simulations are performed to illustrate inadequacies of the commonly used boundary conditions and a modification is suggested that include pressure gradient effects. It is found from this study that the log-law modified to account for the local and instantaneous pressure gradient effects is a better alternative to the conventional log-law and non-slip conditions.

View full abstract

Field observations to investigate the structure of sea breezes have been made on Fukuoka Plain. The intrusion speeds of sea-breeze front are estimated from the distributions of horizontal wind divergence. The wind velocity before and after the arrival of sea-breeze front has been measured by using a Doppler sodar, and the vertical profiles of mean wind speed, standard deviation of horizontal and vertical wind velocities and turbulent kinetic energy have been obtained. They are normalized by using the maximum wind speed and the height at a half of the maximum speed. Especially, the normalization for the wind speed profiles seems to give a good similarity.

View full abstract

The wind systems in Kanto Plain area affect urban heat island and air pollution dispersion of the Tokyo metropolitan area. It is important from the viewpoint of urban planning to grasp surface airflow patterns. In this study, we classified the wind systems by using cluster analysis and diurnal variation patterns. The seasonality of each cluster was also clarified. As the result, most of wind systems in the Kanto Plain area were classified into three types; summer type, winter type and quiet day type. Summer type is prevailed by seasonal south wind and sea breeze. Winter type is prevailed by seasonal northwest wind. Quiet day type which occurs throughout the year is relatively quiet or prevailed by weak Northeast wind.

View full abstract

Turbulence characteristics of boundary layers past gently curved hills with varying roughness height have been studied by wind-tunnel experiments. The results of the mean velocity distributions indicate that for the gently sloped hills, where no flow reversal occurs, the pressure-gradient and boundary curvature effects and the surface roughness act almost independently and the wall-law similarity similar to the rough boundary layers on flat surface exists. The surface roughness, however, is seen to soften the pressure-gradient effects on both mean velocity and turbulent stresses. Furthermore, the turbulence stresses that are known to be highly anisotropic near the solid surface are made more isotropic due to the surface roughness.

View full abstract

Feasibility and accuracy of the dissipation methods for estimating turbulence fluxes of the momentum, sensible and latent heat are further investigated with the turbulence data acquired over the rice paddy field. The dissipation rates of the turbulence kinetic energy and that of the scalar variance are calculated through the Fourier spectrum as well as through the second-and thirdorder structure functions, and these two estimates are compared with each other. The value of the Kolmogorov constant and Obukhov-Corrsin constant are estimated by using structure functions. Validity of Taylor's frozen turbulence hypothesis and the isotropy of the turbulence field in the inertial subrange are also investigated.

View full abstract

The present study uses observational data from a residential site in Tokyo, Japan and a rice paddy in Chiba Pref., Japan, to investigate the relative facility with heat, water vapor, and carbon dioxide are transported by turbulence in the surface layer. The ratios of linear correlation coefficients |rwT/ruw| and |rwq/ruw| increase with stability and the ratios at residential area are generally smaller than at rice paddy due to bluff-body effects. At rice paddy, the ratios of linear correlation coefficient |rwc/rwq| is generally smaller than unity. Meanwhile at the residential area, the distribution of the ratio |rwc/rwq| scatters to |z'/L|. This inequality may be caused by the complex source patterns of the urban surface and the vertical profile within the canopy. Inequalities of transfer between T, c, and q will imply that the diffusion coefficient between them have different value respectively.

View full abstract

This study demonstrates the numerical prediction of thermal sensation index for outdoor environment (SET*OUT) using Regional Atmospheric Modeling System (RAMS). SET*OUT, one of the major thermal sensation index, requires data sets of wind velocity, absolute humidity, air temperature and each component of short wave and long wave radiation in both upward and downward directions. Temporal and spatial variation of SET*OUT over the Kanto Region on August 10 1998 has been presented and discussed. The thermal sensation index for indoor environment (SET*IN) is referred to as a comparison. It is found that the variation of SET*OUT is strongly influenced by mean radiation temperature and sea breeze penetration. The mean radiation temperature, and consequently SET*OUT, have distinctive double peaks in the morning and the afternoon due to the shape factor of cylindrical human body for direct solar radiation. The first peak of SET*OUT in the morning roughly corresponds to the arrival of sea breeze front, and the value is generally larger than that of the second peak in the afternoon. Such a behavior of SET*OUT can be accounted for by the fact that the sea breeze increases wind velocity and activate the heat transfer from human body. SET*IN is similar to but slightly (0.5-1°C) larger than air temperature, which is due to the high humidity condition in Tokyo area.

View full abstract

The purpose of this study is to clarify the role of forest in urban area from a viewpoint of urban environment by observing the leaf temperature and micrometeorological factors, such as air temperature, wind speed, humidity, solar radiation, soil heat, and CO₂ concentration. In the midsummer of August 2000, the micrometeorological observation was carried out at Koishikawa Korakuen Gardens (in Bunkyo-ku Tokyo, Japan) for a week. The following results were obtained: 1) In the daytime, the leaf temperature rapidly lowered, when some critical conditions were exceeded. In the nighttime, the air and leaf temperature were almost the same. 2) When the flux of solar radiation increased above about 400W/m², the leaf temperature lowered linearly with it. 3) Within VPD (vapor pressure deficit) became higher than 4hPa, the leaf temperature rapidly lowered further than the air temperature. 4) Simultaneously with this, the carbon dioxide concentration began to lower.

View full abstract

Initialization of soil moisture is important and difficult problem in numerical weather prediction model. In this study, we use thermal data to estimate soil moisture in land surface model (SiBUC). Temperature and soil moisture are closely related each other through evapotranspiration term which appears in both prognostic equations. So we use Kalman filter to connect these variables in this highly non-linear system.
First step is to formulate filtering system to be used in SiBUC model. State variables are three temperatures (Tc, Tg, Td) and three soil moistures (W1, W2, W3). System equations are prognostic equations of these variables. Observation vector is surface temperature (Tc, Tg) which are expected to be derived from satellite Infra-red image (e.g.GMS5-IR1, IR2).
Second step is to test the system by using the result of control run as observation vector. Changing the initial value of soil moisture, several simulations were executed. In all cases, the system worked to reduce the initial soil moisture error. The system is also tested in JSM-SiBUC coupled model.

View full abstract

In order to investigate the effect of the drop-phase oxidation due to rainout (in cloud scavenging) of gaseous air pollutants on the acidification of cloud droplets, the characteristics of the acidification of a growing cloud droplet by the rainout of SO₂ (g) are simulated numerically with use of a mathematical model based on physicochemical consideration.(NH₄) ₂SO₄is selected for the cloud condensation nucleus (CCN), which is a major aerosol and produced from NH₃ (g) and SO₂ (g) via gas-phase chemical reaction in the atmosphere. With use of the model the droplet radius and the concentrations of chemicals are simulated. It is shown that with lapse of time the hydrogen ion concentration continues to increase beyond the equilibrium concentration (obtained in the case without the oxidation) and that a plateau appears in the concentration profile.

View full abstract

Water qualities of acid rain were investigated on the basis of multivariate analyses and temporal change analysis for the percentage of major ion constituent. Results showed that rain in the rainy season (early summer) had higher NO_3^- and NH_4⁺ percentages than those in other seasons, and that the range of seasonal change of those ions was wider than other ions. Furthermore, the ratio of NO_3^-/nss-SO_4^2-was examined for its relationship with the amount of rainfall and rainfall intensity. Results showed that the ratio was high when the amount and the intensity were small. These results suggested that NO_3^-concentration was sensitive to the effect of rainfall characteristics because it was strongly influenced by washout process.

View full abstract

Chemical composition, hydrogen and oxygen isotopic ratios of precipitation were analyzed for studying water and atmospheric circulation. Precipitations were sampled in Wakayama prefecture at the south of Izumi mountains and also in Osaka prefecture at the north. Cl^- in precipitation sampled at Wakayama, Osaka and Tondabayashi cities were mainly derived from sea. Concentrations of NO_3^- and SO_42-derived from productions accompanied with city activities in Osaka and Tondabayashi cities were higher than those in Wakayama city. The average pH values, 5.2 in Osaka and Tondabayashi cities were lower than 5.8 in Wakayama city.δ D and δ ¹⁸O values in precipitation were very variable with times. In spite of the variation widely, time series of δ D values showed almost the same values in the wide areas (60km) from Wakayama to Osaka prefecture. Therefore, δ D and δ ¹⁸0 values in precipitation were thought to depend on the change of δ D and δ ¹⁸0 values in air.

View full abstract

A multifractal model is used to derive the hourly rainfall distributions from those observed at daily scale for a number of rainfall series observed near Tokyo. With these distributions a cascading model is used to derive a multifractal fields which has similar scaling properties as the original rainfall series. Synthetic hourly rainfall series are generated based on these multifractal field. The results are verified with numerous comparisons with original hourly rainfall distributions. It is proved that the adopted method can produce an accurate representation of hourly rainfall distributions using only daily rainfall as source data.

View full abstract