Considerações gerais sobre a semiaridez do Nordeste do Brasil

Resumo

This work was approved by the XVIIIth International Geographical Congress of August 1956, Rio, and is designed to guide geographical studies in the Brazilian Northeast. It is not a question of essentially climatic observations, but of a series of geographical factors conditioned to some meteorological measurements. They are extremely general considerations with the object of superficially showing the semi-arid and humid differences throughout this Great Region of Brazil.

            Various climatic and geographical factors are compared and also noted in relation to other continents.

            The method chosen to represent these different areas graphically is based in two formulas devised by E. de Martonne, under the name of Aridity Index, viz.:

            I – P/T+10

            and

            II – [(P/T+10)+(12p/t+10)]/2

enabling two comparable charts to be drawn with different values.

            The formulas preferred, among other more real ones, are based on the fact of the Northeast of Brazil being unable to rely on measurements of relative humidity, evaporation and transpiration in sufficient number to accompany the approximate total of 665 meteorological stations corresponding to observations of precipitation and temperature of the atmospheric air at present in existence.

            The charts were plotted on contour maps and an attempt was made to adapt the indices thereto so as to check the accuracy of the various sources from which the data were supplied.

            Close attention was paid to the direction and nature of the various air masses in relation to the position of the stations with regard to altitude, morphology and situation of slopes to leeward or to windward.

            It was found necessary to apply compensation even to the figures established by existing tables, particularly in connection with. the atmospheric air temperature, and this obliged the author to proceed to various interpolations.

            It may be concluded that the semi-aridity of the Northeast is moderate in comparison with other regions of the globe likewise considered semi-arid.

            In the climatic past, however, various phases have occurred when the region was more severely afflicted. Certain morphological characteristics of the semi-arid and arid palaeo-climate are to be found imprinted on the present landscape, e.g.: greatly windworn pebbles and sands, patterns of semi-arid depressions, inselberges.

            The concept of the "northeastern drought" is, therefore, not climatic. The various political demarcations effected by the National Anti-Drought Works in the "Drought Polygon" under consideration have vacillated considerably and fail to agree with the geographical semi-arid areas.