Seasonal change of general meteorological factors in the North Borneo (the state of Sabah and Sarawak in Malaysia) were examined using data measured by the Malaysian Meteorological Service (MMS) in the 10 stations for the past 51 years. Seasonal change of temperature, humidity, precipitation, wind speed, wind direction, solar radiation and evaporation were obvious in this region, especially precipitation. Previous studies tended to have a perception that this region has no clear seasonal change of general meteorological factors because the amplitude of the seasonal fluctuation in this region is smaller than the amplitude of seasonal fluctuation in the temperate region or the amplitude of diurnal fluctuation in the tropics. Long-term precipitation data showed that there are no three consecutive months that have less than 100mm monthly rainfall, and this is the reason why this region was considered to be a region with no seasonal precipitation change despite of the obvious seasonal change shown in this paper.

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Multipurpose dams in Japan are not operated efficiently because of too little storage and too much supply when a river flow successively decreases. This is because they are no operated on the basis of a future quantity at a downstream observatory while they should be. It is proved that dam reservoirs after a flood season could be restored more rapidly than the current operation, if the storage and supply were appropriate. In addition, medium floods in a dry season which are crucial to preserve the ecosystem are less seen in downstream areas after dams were built. This is because the importance of such medium floods is not fully recognized and therefore it has not been designed in such way that they would have the maximum quantity of floods to the harmless extent. It is proved that the maximum quantity would be doubled even at downstream observatories, as the case may be, if the maximum quantity of medium floods could be restored at their natural status. To solve the above mentioned problems, we propose low flow management in dam reservoirs, where for operation of water we compare the normal quantity with the estimated quantity obtained from time-series non-controlled flow, and not store water in reservoirs as long as downstream safety is ensured even when medium floods increase. The proposed method here has been proved efficient and feasible by trial account performed in an actual low flow management.

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This study presents an application of the random cascade model to the evaluation of the transport phenomenon in soil. Dye tracer tests were carried out and dye staining patterns were digitized for the analysis. The dye staining pattern showed heterogeneous response in all of experimental scales, 0.25, 0.50 and 1.00 m. The random cascade model was applied to the dye infiltration patterns and heterogeneous dye infiltration patterns were well described. The lognormal distribution was used to the random cascade generator and conformability result was shown. Maximum dye infiltration depth in case of each experiment was proportional to the experimental scale. Estimated parameter of the random cascade model, σ (standard deviation) showed a tendency of the scale dependency.

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In case of classifying climate over tropical regions, the southeast Asian tropical rainforest region is realized as a rainy region all year round and has no clear seasonal variation in rainfall. The recent study, however, shows that some part of the southeast Asian tropical rainforest region has an obvious seasonal variation in rainfall and the variation have different patterns from site to site. In this study, daily rainfall data observed for 41 years at 17 sites in the state of Sarawak, Malaysian Borneo was analyzed for understanding the spatial distribution of seasonal variation in rainfall and for classification of the region by rainfall climatology. By applying proposed 2 classifications, the seasonal variation in rainfall was classified into 5 patterns in detail. Five seasons were defined based on the seasonal variation of 5 groups and the characteristics of the seasonal variation in rainfall for 5 groups were analyzed in each season.

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A simple scaling algorithm is proposed to rescale fine-resolution river networks to any coarser spatial resolution. To derive flow routing at a coarser resolution, the stream line is traced from the fine-scale grid cell that has the maximum drainage area in the coarse-scale grid cell, to the fine-scale cell in the adjacent coarse-scale cell. When the transit region between the coarse-scale cells is introduced, coarse-scale networks can represent the topology of the original fine-scale network much better. The proposed algorithm is successfully applied to the Hayakawa River basin; coarse-scale networks, at 250m, 500m, and 1km resolutions, are derived from 50m resolution network, and the geomorphologic characteristics of the river network, such as river length, elevation gradient, and width function, are well reproduced. In the case of the Yellow River basin, the aggregated network with a 30×30 kernel preserves the features of the original 1km resolution gridded network with sufficient accuracy.

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