Atlas of Climatic Types in the United States, 1900-1939

Excerpts from the Introduction: Although drought years and flood years cannot be predicted, it is possible by using the many records of the United States Weather Bureau to determine the frequency with which droughts or other climatic events are likely to occur. Such information is of great aid in evaluating the agricultural potentialities of a region. It is essential to effective land use planning and to intelligent evaluation of erosion hazard. It can tell for a particular area whether, over a period of years, agricultural successes can be expected sufficiently often to make continued farming possible. Similar information can be obtained for the grazing regions. Climatic analysis of actuarial type should form the basis for policy and action in regions of high climatic risk, such as the Great Plains. Evaluation of use capabilities of any area should be based on a climatic index. Edaphic factors at one site may to some extent minimize the climatic hazard; at another, they may actually accentuate it. A detailed soil or land-type survey will determine the edaphic variation of the individual field above or below the use capability imposed on the area by climate. The edaphic effect of different soil types is relatively small as compared with the larger effect of differences of climate over the continent. The maps in this atlas are restricted to a presentation of the moisture factor of climate and show the normal position of the principal climatic types, their variation in position from year to year, and finally, the frequency of occurrence of the various individual climates. From a study of these maps, an appreciation of the diversity of the problems of soil and water conservation in the different parts of the country may be obtained.