The Annual March of Precipitation in Arizona, New Mexico, and Northwestern Mexico

Abstract

This report is concerned with the annual march of monthly precipitation amount in an area comprising the states of Arizona, New Mexico, Sonora, Sinaloa, Durango, and western Chihuahua. Fourier analysis was used to reduce the twentyyear mean monthly values to six harmonic terms, four of which were then plotted on charts and studied. The results of this study indicate that an area consisting largely of the Sierra Madre Occidental in northwestern Mexico, and the portion of Arizona southeast of Tucson constitute a single rainfall province with a strong summer maximum of rainfall. This province also has a winter maximum but only in Arizona does the semi-annual term exceed the annual in amplitude. Within the United States the Gila and Rio Grande valleys constitute rainfall provinces of internally similar annual march, while the upland areas tend to resemble the Pacific coastal pattern to the west.