Abstract
Documenting how ground- and surface water systems respond to climate change is crucial to understanding water resources, particularly in the U.S. Great Lakes region, where drastic temperature and precipitation changes are observed. This study presents baseflow and baseflow index (BFI) trend analyses for 10 undisturbed watersheds in Michigan using (1) multi-objective optimization (MOO) and (2) modified Mann–Kendall (MK) tests corrected for short-term autocorrelation (STA). Results indicate a variability in mean baseflow (0.09–8.70 m3/s) and BFI (67.9–89.7%) that complicates regional-scale extrapolations of groundwater recharge. Long-term (>60 years) MK trend tests indicate a significant control of total precipitation (P) and snow- to rainfall transitions on baseflow and BFI. In the Lower Peninsula Rifle River watershed, increasing P and a transition from snow- to rainfall has increased baseflow at a lower rate than streamflow; an overall pattern that may contribute to documented flood frequency increases. In the Upper Peninsula Ford River watershed, decreasing P and a transition from rain- to snowfall had no significant effects on baseflow and BFI. Our results highlight the value of an objectively constrained BFI parameter for shorter-term (<50 years) hydrologic trend analysis because of a lower STA susceptibility.
Highlights
Considered to be in the “bullseye” of climate change, watersheds in the U.S GreatLakes Basin, and in the state of Michigan in particular, have undergone dramatic hydrologic transformations [1]
As typically seen in hydrologic data [70], short-term autocorrelation (STA) is positive (Ljung–Box statistics > 0) for all timeseries, in that, high values are followed by high values and low values are followed by low values
This observation is consistent with the stronger memory effect of slower moving groundwater and baseflow as compared to streamflow that are more influenced by sudden, quickflow responses to short-term rain events [84]
Summary
Considered to be in the “bullseye” of climate change, watersheds in the U.S GreatLakes Basin, and in the state of Michigan in particular, have undergone dramatic hydrologic transformations [1]. Of the hydro-climate time series data used for trend evaluations of water balance parameters, baseflow (defined as the streamflow component sourced from groundwater) is usually not included. This likely reflects the uncertainty associated with the various estimation procedures [11,12] or data shortage from unregulated/undisturbed watersheds [7,13,14]. A comparison of the concurrent trends of hydrograph components through the baseflow index (BFI = ratio of mean baseflow over mean streamflow) allows for an assessment of the relative impacts of climatic stressors on groundwater and surface water resources Baseflow constraints are of key importance in the assessment of water quality and stream biodiversity in droughts [15,16,17,18,19,20,21,22], as well as in the calibration of hydrologic models of groundwater recharge [6,23,24,25,26].
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