The Koppen Classification of Climates in North America

Abstract

T HE Koppen classification of climates has been criticized from various points of view. Some geographers regard it with suspicion because Koppen's climatic divisions now and then show pronounced discrepancies from phenomena of the natural and cultural landscapes. According to this point of view the value of a climatic classification is lost when its criteria are too rigid. As the present meteorological observations are inadequate for a purely quantitative classification, it is maintained, every classification must be empirical at critical points. Hence no appearance of false accuracy should be given by allowing boundaries to depart very far from observable features. Others criticize the Koppen classification for being too empirical. It cannot be denied that the Koppen system is vulnerable on both sides. The rigid application of principles derived empirically has established in North America some theoretical climatic limits that are little more than arbitrary boundaries. The fact that central Massachusetts and central Florida are included in the same climatic region (Cfa), that Spokane, Wash., and Fresno, Calif., are in the same group (Csa), and that Vancouver, B. C., and Los Angeles are companions' illustrates the tenor of a criticism that no student of the landscape can ignore. Considered from the quantitative point of view also, the Koppen classification has obvious shortcomings. The use of mean yearly temperatures to establish the BS/BW and B/H boundaries, the use of empirical constants in the BS/BW and B/H formulas, and the purely empirical choice of thermal limits that establish other climatic boundaries are points that have been touched on many times in periodical literature.2 Although the only serious competitor of the K6ppen system, Thornthwaite's classification, corrects one deficiency, it is just as empirical as K6ppen's at critical points, and much more complicated.3 Evaporation data are derived from monthly, not yearly, means of precipitation and temperature; but the determination of