This study investigated changes in mean and extreme precipitation in the metropolitan area of Milwaukee, Wisconsin in an attempt to find the effects of urban areas on precipitation patterns. Precipitation data were obtained from a gridded (8-km spacing) historical climatic dataset for Wisconsin for 1950-2006. The Mann-Kendall test and the Sen’s slope test were applied to investigate temporal trends. Monthly wind directions were examined against monthly precipitation patterns. Main findings from the study include the following: (1) Annual precipitation significantly increased in the northern part of the study area during 1950-2006, whereas extreme precipitation showed virtually no trends; (2) The metropolitan area showed a distinctive center of low precipitation in selected months; (3) Extreme precipitation showed a more localized pattern than annual precipitation; and (4) Wind directions reasonably explained the spatial distributions of monthly precipitation with respect to the urban area. The results suggest signals of urban influence on precipitation, which need to be corroborated by more detailed investigation on precipitation characteristics.



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