This study emphasized the role of vegetation in land surface processes occurring on the permafrost area on the Tibetan Plateau. In order to understand the effect of vegetation in the energy and water cycle of the permafrost area, albedo on various surface conditions was measured in the north side of the Tanggula Mountains. In addition, evaporation and transpiration were measured by using micro-lysimeters. The surface conditions of five micro-lysimeters were water, bare soil, grass with natural moisture soil, grass with saturated soil, and grass with surface-sealed soil, respectively. The effect of surface conditions was evaluated as surface moisture availability in the bulk transfer equation. Albedo of the permafrost area without snow cover in summer can be estimated as the weighing average of the area ratios of grass, dry soil and wet soil. The albedo at the study site is 0.176. The surface moisture availability of grass with surface-sealed soil decreased with the increase of the vapor pressure difference between leaves and atmosphere. The evapotranspiration of grass with saturated soil is divided into evaporation from wet leaves, transpiration and evaporation from soil surface in terms of surface moisture availabilities. The surface availability of wet leaves ranges from 1.0 to 0.75. The maximum of the surface moisture availability of grass with saturated soil is 0.75, including the contribution of the surface moisture availability, that is 0.18.

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For coping with problems related to soil freezing and thawing, it is necessary to measure the frozen and melted depths accurately. In this paper, the time domain reflectometry (TDR) technique was applied to the measurement of both depths at a dry field lot in Fukagawa, Hokkaido, Japan. Then, the measured values by the TDR were compared with those by the temperature method using thermocouples and the methylene blue frost-tube, which have been used as a conventional method. As a result, it has been shown that the TDR is capable of measuring the frozen and melted depths in both the freezing and thawing processes with satisfied accuracy in actual use. Furthermore, it was found that the soil temperature gradient around 0°C is very gentle in the thawing process, consequently the temperature method is not so suitable for the same measurement in this process because it is difficult to locate the depth of 0°C line.

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The annual rainfall data at Sacramento, Oroville and Shasta in California were tested whether they obey Normal distribution, Logarismic Normal distribution (with 2 parameters) or the distribution with 3 parameters. The last distribution was better than the others in agreement. Then, the calculating method of b, one of the 3 parameters which is added to rainfall data in order to agree with the distribution, was examined to introduce a simple method for founding b in minimizing the square of errors of a distribution graph. However, the Logarismic distribution with 3 parameters has the limit to the agreement, especially around maximum or minimum. Then, a modified Logarismic distribution was prepared and proposed. The new distribution was better than the above in agreement. And the estimation of the errors was proposed in a view point which the errors of the nearer distri bution to the true distribution approached to Normal distribution.

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In Japan especially in urbanized areas, a heavy rainfall in a short period of time and small area can result in extensive damage. But the probable maximum precipitation (PMP) for the river basin is not known. The traditional approach to PMP determination is mainly based on the moisture maximization of observed extreme precipitation amounts. However it is known to have a theoretically weak basis. In this study we focus on the heavy rainfall caused by the strong convective cloud. First, the traditional approach and other approach for PMP are reviewed and it is suggested that an estimating method using a rainfall simulation model is more useful. Next, using the one-dimensional convective cloud simulation model developed by Ferrier and Houze, some simulations are conducted under different atmospheric conditions. And finally the new approach for PMP estimation is presented considering the atmospheric moisture and its instability expressed by convective available potential energy (CAPE).

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A simple parameterization scheme which can estimate momentum, heat, and vapor fluxes from surfaces has been proposed by Kimura. In his scheme, a complex land-use surface is classified into several simple land-use surfaces. After the three fluxes from each simple land-use surface are calculated independently, total fluxes from a grid area representated by one grid point were estimated using weighted average of fluxes from each single land-use surface. Although his scheme is valid on various kind of surfaces, for example, on the area where water surface locates adjacent to arid bare land, that isn't applicable. In this paper, this reason and modified scheme are presented. The modified parameterization scheme which includes advection term is also applicable to the complex land-use surface mentioned above.

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The purpose of the study is to determine the daily and annual variations in the surface heat budget of the arid and semi-arid regions in China. This paper presents a heat balance model for calculating the evaporation, soil water content, soil temperature of the bare soil surface. In the model the transport of liquid water, diffusion of water vapor and vaporization in the soil pores are described. The snow accumulation and melting processes in winter season are also considered. The albedo of snow surface is considered as a function of the air temperature and the elapsed time after snowfall. Soil parameters of the hydraulic conductivity and of the matric potential are determined experimentally. The other estimated results are as follows. The annual values of the potential evaporation are 800-2700mmy-1. The thermal diffusivity of the ground is about 0.2×10-6m2s-1 for the surface layer, and about 1×10-6m2s-1 for the layer of 1.6-3.2m depth.

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The ground heat budget over the bare soil surfaces is estimated for arid and semi-arid regions in China. Calculated values of the daily mean, maximum, and minimum surface temperatures are shown to be in close agreement with the observations. A greater part of the rain water poured into the ground returns to the atmosphere within 5 to 15 days through the evaporation process. The annual mean value of the soil water content increases with the depth, and the increasing rate of it grows larger with increasing annual amount of precipitation, excepting an arid station of Turpan. It is found that the annual amount of evaporation depends on the annual amount of precipitation, i. e., in the arid region it is in proportion to the annual amount of precipitation, and that in the humid region it tends to have a upper limited value which is determined as functions of the potential evaporation and soil hydraulic parameters. In the arid region the soil at a depth about 1 m is able to have a hydrologic memory of the past several tens years because of slow-moving water in the dry soil. Typical results at each station are as follows. (1) At Lanzhou, one of the station in semi-arid region, the sensible heat flux is considerably greater than the latent heat flux in dry season, however, both fluxes have comparable magnitude in rainy season. (2) At Dunhuang in arid region, net radiative flux is in almost equiliblium with the sensible heat flux, except for several days after rain. (3) At Turpan, a station with the smallest amount of precipitation (14 mm y-1), annual mean value of the soil water content does not increase with depth. (4) At Hailar where it has a snowfall in winter, the ground surface temperature has a rising trend after disappearing snow, consequently the sensible and latent heat fluxes increase, then the soil water content shows a marked variable tendency. Simulated snow accumulation and melting processes are shown to be in close agreement with the observation data at the station.

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This study propose an estimation method of the annual changes of monthly actual evapotranspiration (ET) in a meso-scale river basin (100-2, 800km2) by using a complementary relationship equation and Kojima equation, which require meteorological data, Landsat TM data and digital terrain model (DTM). A surface soil moisture index is proposed in order to describe the surface soil moisture as the index of zero to one. This method was applied to the Abashiri and Tokoro River basin in the eastern part of Hokkaido. The influence of some factors, e.g. land cover category, land development, slope direction and air temperature, on the annual ET of the Abashiri River basin was examined. The annual changes of ET and surface soil moisture index in the Tokoro River basin were also estimated.

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The “Zambezi Agreement” was developed by guidance of the United Nations Environment Programme (UNEP) and signed by ministers, in charge of environment, of five basin countries in 1987. The “Zambezi Agreement” was for promoting environmental management of the common Zambezi river basin and was a harbinger of the “Agenda 21”, which called for development of national action plans for intergrated management of water resources and coordination among riparian contries for an intemational water body. The implementation of the “Zambezi Agreement” has however been impeded due to following causes: (1) only those ministries of basin countries in charge of environment supported the “Zambezi Agreement” and little financial resources were made available for its implementation within countries, (2) UNEP was unable to provide funds for implementation due to its institutional mandate, a coordinating body rather than an executing organization, within the United Nations family, (3) the Soil, Water and Land Conservation Unit of SADCC, which was made responsible for implementation, lacked both institutional and financial resources, and (4) the projects listed in the “Zambezi Agreement” were too general to draw attention of donor countries and organizations.

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