Climatic Controls and Spatial Variations of Precipitation in the Western United States

The western United States is characterized by complex seasonal precipitation regimes due to the hierarchy of climatic controls that operate at different spatial scales. A climatology of month to month changes in precipitation, using data from 4027 stations, illustrates how different climatic controls govern the annual cycle of precipitation response and explains the spatial distribution of the seasonal precipitation maximum. These results particularly indicate that smaller-scale climatic controls must be considered along with larger-scale ones in order to explain patterns of spatial climate heterogeneity over mountainous areas. The examination of seasonal precipitation maxima during years characterized by abnormally low winter Pacific-North American teleconnection (PNA) patterns and abnormally strong summer monsoons reveal few changes spatially as compared to normal. The lack of changes illustrate that spatial heterogeneity of precipitation seasonally is the rule rather than the exception for much of the mountainous West. The results of this study offer important implications for scholars interested in assessing spatial climatic variations of the western United States at timescales ranging from interannual to the late-quaternary.