Peak streamflow trends in Michigan and their relation to changes in climate, water years 1921–2020

Abstract

This study characterizes hydroclimatic variability and change in peak streamflow and daily streamflow in Michigan from water years 1921 through 2020. Four analysis periods were examined: the 100-year period from water year 1921 through 2020, the 75-year period from water year 1946 through 2020, the 50-year period from water year 1971 through 2020, and the 30-year period from water year 1991 through 2020. Peak streamflow and climate data were available at 4, 29, 50, and 30 streamgages in the 100-, 75-, 50-, and 30-year periods, respectively. Daily streamflow was available for 4, 29, 74, and 79 streamgages in the 100-, 75-, 50-, and 30-year periods, respectively.Peak streamflow for each streamgage and analysis period was assessed for monotonic trends and change points. Trends in peak streamflow were predominantly upward, with some isolated downward trends throughout the southern half of Michigan for all four analysis periods. Trends in the Upper Peninsula were downward in 75-and 50-year analysis periods and upward or neutral in the 30-year period. Upward trends in peak flows were largely driven by increases in precipitation, which occurred at nearly every streamgage in all analysis periods, with the greatest magnitude trends in winter and spring in the 50-and 30-year periods.Analyses using daily streamflow included tests for monotonic trends in annual and seasonal average streamflow, peaks over thresholds analysis, and center of volume analysis. Annual streamflow patterns were similar to peak-streamflow patterns, with primarily upward trends throughout the lower peninsula in all analysis periods, downward trends in the Upper Peninsula in the 75-and 50-year periods, and upward trends in the Upper Peninsula in the 30-year period. Seasonal trends in streamflow varied by analysis period and region. In the 30-year analysis period, upward streamflow trends in spring were likely from increases in winter and spring precipitation, whereas neutral and downward trends in fall and summer in the southern part of the State were due to increasing temperatures in fall and summer.