The writer recently studied the influence of wind direction and earth features on the distribution of rainfall in the Nabeta river valley, which is some 1000m long, by closing the observational network. The amount of precipitation was measured wherever a rain-gauge had been installed, soon after the rain, which sometimes continued for several days, had stopped.
The records of every rain were plotted by isopluvial lines on a topographical map, with the result that 51map sheets were obtained during the interval from May 1936 to April 1937. The writer classified these maps according to the direction of the prevailing wind, which was determined by means of the lower clouds at 10 o'clock every morning At the bottom of this valley-floor all the prevailing winds are apt to bend and blow under topographical influences in two main wind directions, i.e. NE, E, SE→SE (upwards) and SW, W, NW, N→NW(downwards). During a rain, instead of measuring directly the mean direction of the wind by means of self-recording weather vanes placed in various parts of the valley, we found the mean direction indirectly by marking on a map the values of the rain-fall for the places in question and determining its particular type. The latter is easy and inexpensive, while the former is difficult and troublesome.
We thus found that the drift of the observed values of the rainfall for these various places in the valley are equivalent to the deviation in direction of the mean wind for these places from the prevailing wind direction.