A Precipitação efetiva deduzida da lei de Van't Hoff

Resumo

José Setzer, chemical engineer, and pedologist in the Geology Department of the School of Philosophy, Letters and Science at the University of São Paulo, presents in this article interesting thoughts about a perfection of climate classification as conceived by C. Warren Thornthwaite. It consists of a new interpretation of the effective precipitation used by Thornthwaite.

            Setzer, basing himself on Van’t Hoff’s well-known law, which states that - the speed of chemical reaction doubles when the temperature rises above 10 degrees Centigrade -, gives the subject a different treatment from that of Thornthwaite. The author shows that it is an error to consider the influence of temperature on biology as proceeding according to a linear law suggested by the linear scales of the thermometer. The temperature influence referred to obeys, in reality, the exponential functions. Thus, the minimum, ideal and maximum temperatures are, in the physiological sense, equidistant from each other only which usually varies between 1.05 and 1.14. The use of the thermometer linear scale brings the maximum temperature much closer to the ideal than to the minimum temperature, which does not actually correspond to physiological facts.

            The author using Vant’s Hoff’s law, presents a new formula to calculate effective precipitation. It is a formula of a function of the exponential type which furnishes geometrical progression whose values serve as the basis to restrict the climates according to the degree of humidity. In order to facilitate the calculation of these progressions, the author constructs abacuses and graphs that are found in the text of the article.

            In summarizing,. José Setzer accepts the classification of Thornthwaite introducing only a modification in the method of calculating effective precipitation, which constitutes however an advance of real value.