The DSL bulk method was examined if it is applicable to an arkose sand, which method was devised to measure the rate of evaporation from dry soil surfaces by remote sensing and substantiated to be effective by applying it to the Tottori-Dune sand (He and Kobayashi, 1998). The result of the experiment shows that the DSL bulk method is also effective for an arkose sand by adapting the coefficients of the formulae to the soil.

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Estimation of Leaf Area Index (LAI) based on satellite data was examined to observe the amounts of forest leaf. The main results are summarized as below.(1) Comparison with Normalized Differential Vegetation Index (NDVI) based on the satellite data and LAI based on indirect method shows good relationship for broad range of LAI.(2) The LAI map in Japan estimated from NOAA data shows good agreement with literature data for several forest types. This LAI map has the highest resolution (1-km) in Japan. From the above results, it was found that the indirect measurement is applicable to the observation of LAI, and LAI estimation using satellite data is reliable as compared with literature data.

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During the preliminary observation of GAME-T (GEWEX Asia Monsoon Experiment Tropics), enhanced rawinsonde observations were performed for 2 weeks in rain and dry seasons, in 1996 and 1997, at various stations in Thailand by NASDA/EORC. From the atomospheric data, the area composed of 3 observation stations is defined, and vapor flux convergence and the difference of precipitation and evapotranspiration within this area are calculated using atmospheric water balance method. Comparing them with those calculated from 4DDA data, at 6 hourly or one day interval, those from observation data varies extremely and both the positive and negative peaks are bigger. However at 2 weeks intervals of observational period, both corresponds fairly well. From vapor flux convergence calculated from observation data, it is found that there were the peaks of convergence at the layer from 850hPa to 700hPa in vertical direction. Further, using precipitation data, large area evaporation is estimated based on observational data and from 4DDA data. Comparing it with pan evaporation data, it is found that evaporation for 2 week mean seems realistic. In the caluculation of observational data, both the usual data composed of only standard pressure level ones and the data composed of standard pressure level and particular level ones are used, and it is found that there is a little differnce between these 2 kinds of data.

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This paper describes how to determine two parameters, i.e., the time constant of separation Tc and the damping rate δ, for the filter separation AR method and how to estimate the initial river discharges, which is first subtracted from the original discharges. Through comparisons of the absolute errors of the surface and sub surface flows separated to the reestimated ones and of the corresponding response functions for possible combinations of Tc and δ the followings are found: For hydrograph having long recession periods in Kanna river, there is a definite area with the smaller absolute errors relating to Tc, though the error is insensitive to δ. The initial discharges could be predicted by agreement of the time constants giving the two ends of the definite area with the ones giving the two adjacent minimum extremes of the coherence between the rainfall and discharges.

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This paper deals with an actual condition of irrigation water management under extraordinary drought conditions in the West Japan in 1994. The drought was very severe to the extent that there were some areas with more than 1000-year return period of cumulative rainfall from June to August. Firstly, issues encountered with the Water Allocation Council (WAC) during drought conditions are presented: organization of the WAC under drought conditions; reducing industrial, domestic, and irrigation waters; procedures for deciding water saving ratios among four representative basins with respect to time; relevant water storage ratios among irrigation reservoirs; relationships between storage ratios and water saving ratios; and evaluation of water saving measures by the Land Improvement Districts (LIDs). Secondly, measures through controlling diversion works by both the LIDs and farmers are proposed. The measures by the LIDs and farmers are divided into two categories. The first is distributing the available water according to historical allocation. The second is compensation for shortage from supplemental resources such as drainage water or ground water aquifer. Thirdly, the subsidies by the Prefectural Government and the Ministry of Agriculture, Forestry and Fisheries are explained. Finally, the relationships between irrigation water and other utilities are summarized, and a market mechanism is proposed for more efficient use of water in the future.

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