The Climates of California According to the Koppen Classification

HE Geographical Review recently published a map by E. A. Ackerman showing the distribution of climates in North America according to the Koppen classification.' The small scale of this map necessitated considerable generalization in the mountainous West and along the Pacific Coast. A more detailed map of the distribution of climates in California is thus considered a desirable supplement. The presentation of a climatic map of California according to the Koppen system may seem superfluous in view of the fact that R. J. Russell published such a map fifteen years ago,2 which has been reproduced in part in this journal.3 Russell's map, however, was based on the old delimitation of dry climates (for regions with winter rains: N = t + 22, N being the annual precipitation in centimeters and t the mean annual temperature in degrees centigrade), which made steppe areas more extensive than the delimitation now in use (for regions with winter rains: N 2 t). Russell furthermore introduced a subclimate Cs'ab, transitional between the Csa and the Csb zones, which obliterates the boundary between these more commonly accepted climates and complicates the distributional pattern unduly. Thornthwaite4 has shown that the use of the formula N = t + II in place of the equation N = t/2 + II in the delimitation of the desert climate led to an exaggeration in the size of the desert areas on Russell's map.5 This mistake turns practically all of the San Joaquin Valley, with its vineyards and orchards of deciduous and Mediterranean fruit, into a climatic desert. Ackerman's map perpetuates this erroneous classification of the San Joaquin Valley as a desert, though the lack of a transitional belt of steppe climate surrounding this desert area and the general correspondence in shape, location, and size of Ackerman's desert area in the San Joaquin with an area of steppe climate on K6ppen's map in the Handbuch6 point to a possible oversight in the shading of the map. The distribution of climates in California is here presented in two forms: one (Fig. 3) adheres to the Koppen classification currently in use; the other (Fig. 4) embodies the modifications suggested by Ackerman. The two maps differ only in the size of the Ds areas and the subdivision of the dry areas according to temperature

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