Site-specific crop management requires consideration of the spatial variability within the field. Spatial distributions of soil and canopy properties at the field may affect yield potential, hydrologic response, and solute transport. Thus, describing within-field variability is a fundamental first step toward determining the size of management zones. This study is being conducted at an arable flat cassava plantation area in northeast part of Thailand. Soil is generally Rhodic Kandiustox, and its texture is clay. Dry bulk density, volumetric soil water content, Leaf area index (LAI), and plant height were measured at mesh points on site. Dry bulk density and volumetric water content were measured at depth 0-6 cm. Statistical and additional geostatistical analyses were applied on the measured properties. The correlation coefficient between LAI and plant height was significant. Spherical model best fitted all the experimental semivariograms. The range values of the measured properties were about 30 m. All the measured properties exhibited strong spatial continuity. Among the measured properties, LAI exhibited the strongest spatial correlation; plant height exhibited the weakest spatial correlation. The cross-validation showed the goodness of the fitted semivariogram models. The semivariogram model of the dry bulk density was used to estimate the distribution of soil hydraulic parameters in the field. Distribution of soil hydraulic properties across the field can be combined to give a useful input for numerical models to simulate water movement and distribution.

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To investigate the regional characteristics of the change in snow amount in the course of the global warming and its mechanisms, observational data and climate model results are analyzed. The observed trends of snow depth are categorized into two types. The first is a substantial decrease throughout the snow-cover period as seen over most of Canada and to the south of 60°N of the former Soviet Union. The second is an increase in winter followed by a decrease in the snow-melt period as seen over the inland to the north of 60°N of the former Soviet Union. The modeled regional characteristics of trends of snow water equivalent have substantial similarity to the observed trends. To investigate the mechanism of this modeled regional characteristics, the change in snow budget in the model results are analyzed. In the region where the snow water equivalent decreases throughout the snow-cover period, the snowfall decreases due to the decreased ratio of snowfall to the total precipitation in spite of the increased total precipitation and the snowmelt increases. In the region where the snow water equivalent increases in winter, on the other hand, the total precipitation increases as the form of snowfall in winter and the snowmelt in winter keeps almost zero.

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In the study of river hydrology, particularly fluctuations in run-off, the relationship between the diversity of benthic organisms and that has rarely been demonstrated. Here we report the findings of a 20-year study of the diversity in the benthic fauna of the Aki, Hirai and Kita-asakawa rivers in Tama-river system that has been undertaken by the Tokyo Metropolitan Government from 1980 era. Differences between natural and artificial impacts were assessed by comparing faunal diversity data for dates on which disturbances occurred against data obtained on days when samples were taken. Statistical analysis revealed a strong relationship between flood disturbance and the diversity benthic organisms. Consequently, it was found that flood disturbances of moderate scale could be explained using a probability of exceedence flow regime curve (Q95) and the Simpson index, and that these could be described using a parabolic function over protruding

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In order to determine hydrogen and oxygen isotopic composition of various water samples and to maintain high analytical performance for long-term, the management system including sample treatment, quality assurance of data and specific data management software are developed. Long-term results since 2003 indicate that reproducibility for hydrogen and oxygen isotopic composition are being kept as 0.5 ‰ and 0.03 ‰, respectively.

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Fukuoka Metropolitan Area, a fast growing economic and cultural center in Kyushu, was struck by severe droughts in 1978 and 1994. This area has a geographical disadvantage to supply sufficient water. Although there are many rivers in the area, they are all small with insufficient and unstable discharge due to the small catchment areas. The water taken from the Chikugo River, which is located outside of the area, supplies about one third of the total water demand through the Fukuoka District Waterworks Agency.
The 3rd severest drought struck the Chikugo River basin in 2002. However, water supply for the Fukuoka Metropolitan Area was not seriously affected by the drought.
In this study, the reservoir operations by the authorities during the drought were investigated. Besides, the variation of the water storage of Egawa and Terauchi reservoirs in the Chikugo River basin without Yamaguchi Reservoir was simulated. The amount of water deficit was calculated through the simulations, and the effect of the reservoir on the drought was evaluated. It was found out that the Yamaguchi Reservoir played a significant role for drought operation. If it had not been for the Yamaguchi Reservoir, the stored water that this agency owned at Egawa and Terauchi reservoirs would have been vacant. As a result, the Yamaguchi Reservoir has a great effect on avoiding water rationing in Fukuoka Metropolitan Area.

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Number of researches of climate simulation and climate prediction using high-resolution regional climate models (RCMs) are recently increasing, in relation to monsoon researches or global warming studies. Since RCMs have higher resolutions compared to conventional GCMs, they are able to represent realistic regional climate more in details. Thus, it has become popular among hydrologists, to utilize RCMs as a dynamical downscaling method. In this review, I try to summarize the trend of RCM researches in the latest few years, as well as the characteristics of utilized RCMs. From the beginning of researches using RCMs, it has been stressed that (1) we can improve precisions of the orographical precipitation by increasing the resolution of the model topography. However, (2) the accuracies of the RCMs' results are also strongly controlled by the mother GCM. Moreover, (3) the necessity of urgent preparation of high-resolution and high-accuracy observational data, comparable with those of RCMs, has been emphasized. We also should note that, (4) as for the treatments of physical processes in RCMs, they are improving but still in progress.

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The authors have been insisted that scaling property in Hokkaido region, which is the northern region in Japan, is almost simple scaling. Simple scaling is a scaling feature for regions where snowmelt-generated flood is dominant. On the other hand, multiscaling is a feature for regions where storm-generated flood is dominant.
In this paper, the authors tried to more rigorously investigate it than previous papers which the authors published. As a result, a likelihood ratio test indicated that a characteristic parameter which dominates properties of multiscaling is not zero in this region, viz., scaling in Hokkaido region exhibits multiscaling, In addition to this result, the authors investigated flood characteristics in Hokkaido region and concluded as follow: flood data in this region suggest belonging to multiscaling framework, but data exhibits ‘stronger’ simple scaling than other regions in Japan. According to this conclusion, the authors calculated each scaling exponent (which respectively corresponds to each return periods independently; say, 10yrs, 100yrs, 1000yrs....) which is the slope of equation for logarithm of catchment area and that of flood discharge. After that, the authors carried out inundation simulation, and obtained flood hazard maps in the Ishikari basin. The outline of making process of flood hazard map is as follows;
1)calculating flood discharge for return period T(yrs) for each gauged basins;
2)obtaining each scaling exponent for each return period; regional flood frequency analysis;
3)transferring flood discharge from gauged basins (observation station) to ungauged basins (location):
4)carrying out inundation simulation.

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This study analyses the spatial distribution and interannual change in grain production in the transect along 38°N of North China Plain (NCP) by using statistical data at county level and evaluates the interrelationships among grain production, land condition including groundwater resources, climate, and socio-economic factors. The western part of the NCP shows high and stable productivity of grain production, which is highly determined by the availability of fresh water from groundwater flow system in alluvial fan. Whereas the eastern lowland shows low and unstable productivity, caused by high total dissolved solids (TDS) concentrations in shallow groundwater. The zones of the high TDS concentrations in shallow groundwater were formed at discharge areas of groundwater flow systems corresponding to geomorphologic units. In the lowland area of eastern NCP, grain productions are sensitive to climatic variation because of the low availability of fresh water. The local hydro-geomorphological and hydro-geological characteristics are the fundamental elements in understanding grain production. Secondly, grain production in every county has an increasing trend until the middle of 1990s. This corresponds to the increase in productivity per unit area owing to the improvement of agricultural technology. The stagnancy in grain productions in late 1990s suggests the influence of the cost for grain productions. The consistent steady decline of watertable will promptly raise the pumping cost. This phenomenon may become a limiting factor to grain production in the future when the ultimate level of water stress is reached.

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The hydraulic and morphological characteristics of the Lower Mekong River were investigated. A concept “segment division” was used in this study. Based on the concept, data analysis was conducted using existing data collected. The average bed elevation, average water depth, river width, representative diameter of riverbed material, friction velocity, etc at each cross section at average annual maximum discharge were obtained and their longitudinal changes in the whole Lower Mekong River were shown. As the results, in segment 3 from river mouth to downstream of Tan Chau, river was horizontal and average width was 1,239 m. In segment 2-2 from Tan Chau to Kratie, riverbed slope was 1⁄25700, representative diameter of riverbed material was 0.17∼0.76 mm (fine sand∼coarse sand), and average width was 1,645 m. The relationship between the non-dimensional tractive force and representative diameter in the Lower Mekong River in case of representative diameter 0.17∼0.76 mm was clarified.

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Monthly and event precipitation samples were collected at Tsukuba, and isotopic compositions of oxygen and hydrogen were analyzed for all samples. The isotopic compositions of event precipitation have no remarkable trend of seasonal isotopic change. In regard to the d-excess, however, the cyclic variations are observed, and the values of d-parameter are relatively low in warm period (from April to September) and relatively high in cool period (from October to March). It is confirmed that the temperature effect of isotopes in precipitation exists at Tsukuba from November to March. The isotopic compositions which were calculated by class of precipitation amount show the existence of amount effect obviously. Result of regression analysis indicates above consequence. In cases of snowfall, precipitation from Baiu front and autumnal rain front, the isotopic compositions of precipitation are relatively lighter than those of other cases.

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This study investigated effects of differences of the processes of direct measurements of leaf area index (LAI) and their combinations on the estimation of LAI for planted stands of Japanese cedar (Cryptomeria japonica D. Don). The processes consist of selection of sample tree(s), sampling of leaves, and planimetry of leaf area. Each process has several methods, therefore, estimated LAI will have variations. As for a selection of sample tree(s), estimated LAI was smaller than 10% when a sample tree was only one, in comparison with selecting three sample trees. In this case, the possibility of underestimating LAI is implied when only one sample tree is selected in the stand which represents the average basal area. As for sampling of leaves, the estimated LAI was 10% larger than that by the clipping method, when 1% of the total leaves were selected for the planimetry to consider the labor efficiency. As for planimetry of leaf area, empirical equations between specific leaf area (SLA) and the diameters of leaves were used. In this process, the difference of estimated LAI was within 5% when the sampled leaves were classified to pre-determined classes of the diameters of leaves, in comparison with the usage of averaged diameter of the leaves. Although the differences of estimated LAI in each process was not so large, the accumulation of these differences led to as large as 40% of estimated LAI, even in the planted stands of Japanese ceder which were taken care of such as pruning or thinning.

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Numerous studies have been performed to examine forest evapotranspiration based on flux measurements since 1990s. However, no paper has clarified what was obtained by these studies. This paper answered the question. The authors assumed that the ultimate purpose of forest evapotranspiration research was to predict evapotranspiration rates from any forests. For this purpose, we firstly need to formulate evapotranspiration rates as functions of meteorological factors and model parameters, and secondarily need to relate the model parameters to forest properties (e. g., broad-leaved/coniferous, leaf area index, canopy height, etc.). The first step had been already accomplished before 1990s. The second step became possible by the presence of the studies with flux measurements, because the second step required accumulation of evapotranspiration data from various forests with different properties.

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