山岳

Measurement of the volume of precipitate d water on the earth's surface is an important division of the science of hydroclimatology. Rainfall measurements provide fundamental knowledge needed in establishing the bio-climatic type of a region, and rainfall data are essential in many forms of land management, either for agriculture, municipal development, production of hydroelectric power, or flood control. Rainfall cannot be measured directly, like the flow of a river, but must be estimated from samples taken at various locations on the watershed. For a satisfactory estimate, the individual samples must be as accurate as possible and closely representative of the areas to which they are applied. The technique of precipitation measurement in populated areas, which are usually of minor relief, has presented but little difficulty. On the other hand, precise determinations of rainfall in mountainous regions present many difficulties. Sampling techniques and instrumentation require modification as measurements are extended into the high country, to provide basic hydrologic information for use in water supply problems, stream regulation, and flood control. In this report are presented the results of detailed research of this process and how much precipitation is delivered to mountain watersheds. In 1955, in the Kujiu, central part of the Kyushu, the author started a program of hydrologic research. The area was selected for the investigations included Waita conical mountain situated in the Kujiu mountain within the national park. The research program required an accurate determination of the rainfall on mountain water sheds. In effect, in the high mountains the measure o f total precipitation is in error if one multiplies the horizontal projectional area of the watershed by the total depth of water as given by the conventional vertically placed rain gauge. Storm rainfall must be considered as a vector and the true rainfall sample can be computed by the elementary theory of vectors on the condition that the magnitude and direction of the storm vector in space are known respectively. In steep mountain regions as Waita the conventional rain gauge will not give a true sample of the rainfall. The sample is in error because in mountainous regions storms are usually accompanied by strong winds. The rainfall characteristics study is dealt with the behavior of rainfall in relation to wind. Rainfall rate, wind direction, and wind velocity were recorded synchronously. The vectorical components of rainfall were measured by a directional rain gauge, or special vectopluviometer. It consisted of a horizontal (H) and a vertical funnel (E. S. W. N.) mounted, and rain caught by the funnels was directed into separate compartments of the receiver tank, one compartment for each quadrant of the compass for each funnel. The angle of inclination of the rainfall ( i ) from any quadrant was calculated by the formula, tan i =V /H where V is the catch of the funnel with its rim in a vertical plane, and H is catch of the funnel with its rim in a horizontal plane. The average inclination of the storm could be determinded by summing the catch of the vertical and horizontal funnels separately, and then applying the formula (Table 14, Fig. 60). Correction of rainfall estimated from these vertical rain gauge setting on steep terrain was made possible through the use of vector equation, provided slope and aspect of the terrain are known and storm direction and angle of inclination of the rainfall can be determined. And then author's analysis of measurements of rainfall made during 1955-1961. in Kujiu drainage basin on the windward and leeward slope of the Waita mountain shows that the rainfall at each gage correlates according to a geometric progression with distance of the gauge from the summit (Figs. 28-41). And then the detailed observations made during the microhydro-climatological survey of soil and plant of this Waita mountain district which was undertaken between 1955 to 1961 with aid of agricultural-meteorology. A few of the items are given here. (I) Insolation, air temperature, soil temperature, precipitation, evaporation, and wind difference owing to topographies (Figs. 68-80). (II) Soil and plant variation by topography in the around Waita mountain (Figs. 82-89).