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5— THE IN^TENSITY-DISTRIBUTIOX OF RAINFALL 

 OVER THE WITWATERSRAND. 



By H. E. Wood, M.Sc 



[Abstract.] 



The rainfall records for the period of ten years 1897 — 1906 at a 

 large number of stations within the Central Witwatersrand district 

 of the Transvaal have been treated statistically, and compared with 

 a ten years' series of rainfalls recorded at the Greenwich Observatory, 

 England. Tables have been deduced giving the mean probabilities 

 of daily rainfalls of varying intensities in the two regions. The 

 comparison shows that over the Transvaal excessive rainfalls are to 

 be expected with varying degrees of probability in each of six 

 months of the year, while in England similar rainfalls are only 

 likely to occur in three months out of the twelve, and with a much 

 smaller degree of probability. A further comparison-table shows that 

 only 20% of the Transvaal rainfall falls in what may be classified 

 as light, directly beneficial showers, against roughly 50% of the 

 English rainfall ; whilst about 60% of the Transvaal rain falls in 

 heavy showers against only 25% of the English rainfall. It is 

 therefore inferred that the greater part of the Transvaal rainfall 

 is not directly beneficial to the soil, and, unless conserved, is lost 

 to the Colony. 



Finally a suggestion is made as to a system of measuring the 

 rainfall distribution of any region on a certain scale, following a 

 mechanical analogy. This system applies the figure 5p to the Trans- 

 vaal rainfall and 36 to the English rainfall, the numbers being 

 intended to be roughly inversely proportional to the beneficial value 

 of the rainfall distribution. 



