A statistical analysis of streamflow trends for the state of Michigan

Michigan has a unique landscape that is surrounded by the Great Lakes forming two peninsulas, and encompasses 36,000 miles of inland streams and approximately 11,000 inland lakes. The rare landscape of Michigan makes water its primary commodity and resource. It is imperative to have an understanding of how this resource varies within time and space for water resource management purposes. Therefore, a time series analysis was performed on the USGS streamflow gauging stations found across Michigan in an attempt to identify long-term streamflow trends. Also, the streamflow data were compared to precipitation data of equal length to help identify if a cause-effect relationship exists. Using well-known hydrological statistical techniques the intent of the study was to provide insight into temporal streamflow trends and their interaction spatially. The streamflow and precipitation data were evaluated on daily, seasonal and annual time scales. The analysis proved to be most accurate at predicting trends based on the annual evaluation. The data identified that the majority of stations in the Lower Peninsula experience an increasing trend, while the stations in the Upper Peninsula display a decreasing trend. The relationship between precipitation and streamflow was found to have a direct correlation when both datasets were found to have increasing trends. In addition to precipitation, elevation and land use were found to have a direct correlation with how trends interacted spatially. Some unique cases do occur where trends in streamflow and precipitation opposed one another. Hypotheses for the opposing trends at these locations are provided however these regions require further study and analysis.