The splashing energy of natural rainfall
2000
Matsuda, M. (Nagano-ken. Nature Conservation Research Inst. (Japan))
The energy released by the raindrops of natural rainfall was estimated by analysing data obtained by using a raindropmeter installed in Takamatsu (Kagawa Pref. Japan). From this data, relating to 135 periods of rainfall, it became clear that the size distributions of natural rainfall in terms of volume and energy are suitably expressed by upper-limit equations, and that the modes of both frequency distributions differ from each other, i.e. the same amount of rainfall (volume) does not always release the same amount of energy. Because of this a binomial expression of rainfall (mm/unit time & Joul/square m/unit time) is proposed. The relation between rainfall intensity(I) and its energy(E) was expressed by E=alphaIbeta where alpha varies with dropsize distribution and beta is almost constant. The seasonal variations in the dropsize distributions of rainfall were examined to show that the dropsize distribution of rainfall in the first half of the year is quite different from that of the latter half in Japan. The results indicate that the potential of rainfall in the latter half of the year to cause soil erosion through splashing energy is approximately twice that of rain which falls in the first half of the year. This phenomenon suggests that the prevention of soil erosion after harvesting in Autumn is vital to land conservation, especially in the case of sloping land.
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