A New Formula for Precipitation Effectiveness

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Abstract
While investigating soil genesis in Sao Paulo, Brazil, the author mapped certain climatic elements of this and neighboring regions. The maps provided a clue to differences in the physical and chem. properties of the soils originating from similar rocks under different climates and also guided the development of certain ideas on the negative or positive effects of climatic factors on various important crops grown on the principal soil types of the State. From the data of 110 meteorological stations, the author prepd. annual and seasonal rainfall maps, maps for the rainiest and least rainy months, and similar ones dealing with mean temps. In compiling them, interpolations were necessary and pedologic conditions were also taken into consideration. Besides these and other climatic maps, maps of Sao Paulo were drawn in accordance with Koppen''s international classification, Sere-brenick''s Brazilian classification, and Thornthwaite''s classification based on temp. efficiency and precipitation effectiveness. Use of the last suggested the possibility of deducing a new formula for precipitation effectiveness, based on the well-known law of Van''t Hoff. The author believes that the empirically derived geometrical progression here presented and discussed gives a more rational climatic classification. "Whatever the progression employed, it must be empirically obtained; for the influences of humidity and temperature bear on so many interacting phenomena that the possibility of simple mathematical elaboration is virtually precluded. The question is that of the influence of those climatic factors over a large and complex combination of phenomena and their interactions, so that only an empirical treatment can be satisfactory. The bases, however, can be established by a well-known general chemical law.".

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