Regionalization, seasonality, and trends of streamflow in the US Great Lakes Basin

Analysis of historical streamflow trends and their relationship to landscape characteristics is essential for understanding geographic differences in runoff within the Great Lakes basin and for distinguishing temporal trends from temporal variance. Factor analysis of streamflow records (1956–1988) from 32 US Geological Survey gauging stations within the Great Lakes basin revealed distinct spatio-temporal patterns of stream runoff within five different regions of the basin. Streams represented by the first annual factor occurred in southern Wisconsin and the lower peninsula of Michigan, and exhibited a linear increase in mean annual streamflow over the 33 year period caused by increased autumn and winter runoff. The second annual factor represented streams in New York and eastern Ohio, which exhibited sharply increased autumn discharge during the 1970s and 1980s. The remaining three annual factors distinguished groups of streams in western Ohio, Minnesota, and the upper peninsula of Michigan with differing annual and seasonal flow patterns but no consistent trends in annual flow. Factor analysis of monthly flow expressed as a proportion of annual flow identified three seasonal proportion factors that were temporally distinct but geographically dispersed. Annual yield (annual streamflow per unit watershed area) was greatest from watersheds with greater topographic relief and forest cover, and February yield was greatest from small, lower elevation watersheds having a small proportion of wetland area. Understanding past spatio-temporal patterns of streamflow variability within the US Great Lakes basin and their relationship to landscape properties provides a basis for evaluating future change.