Hydrologic regionalization to assess anthropogenic changes

Within the past few decades, Minnesota's land use change has responded rapidly to prevailing economic growth conditions, resulting in hydrologic characteristic alterations of the landscape and shifting the hydrologic balance of its watersheds. Regionalization using mean annual and mean monthly streamflow values was used to delineate hydrologic regimes with distinct temporal flow variations. By identifying hydrologic relationships between watersheds through an initial regionalization of mean annual streamflow time-series data, hydrologic regimes, each composed of watersheds with common hydrologic controlling variables, were identified. This paper summarizes how by applying factor analysis techniques to complete a statewide regionalization for Minnesota, hydrologic regimes were identified, each with a specific hydrologic signature; varying between three and four runoff periods of different durations. A geographic information system database was established to display the results of the regionalization and to identify hydrologic regime changes between the 1936-2008, 1936-1980, and 1950-2008 analysis intervals. Results delineated five hydrologic regimes for each of the three analysis periods. By focusing on each specific regime, further analyses were completed to identify significant increasing and decreasing trend characteristics. Review of the temporal variation for each regime using Kendall Tau trend analyses suggests that although variation in annual precipitation has an important influence on hydrologic variability, land cover and management proved to be a more direct controlling agent. Understanding the consequences of anthropogenic land use change on hydrologic processes within each defined regime should be the focus of future analyses.