Effects of hydrological forcing on short- and long-term water level fluctuations in Lake Huron-Michigan: A continuous wavelet analysis

Abstract

Understanding water level fluctuation patterns in the Great Lakes is one of the pillars for designing adaptive management practices that can mitigate the impacts of extreme water levels on shoreline infrastructure and associated economic activities. The present study uses continuous wavelet transformation to conduct a two-dimensional frequency-scale spectral analysis on monthly water levels in Lake Huron-Michigan. Consistent with past work, we detected 1-, 8-, 12-, and 36-year quasi-state periodicities in water level records during the 1860–2015 period. The wavelet analysis revealed diminishing, re-emergent, and/or intermodulation patterns in the long-term periodicities, but the 1-year cycle has persisted throughout the temporal domain studied. While the features of the dominant frequencies are consistent with previous findings, the consideration of wavelet ridges with the continuous wavelet transformation yielded a complete picture of evolution in time–frequency domain that is impossible to achieve with the same accuracy using conventional signal processing methods. Continuous wavelet transformation and analysis of wavelet coherence between hydrological and water level changes signified the role of runoff and evaporation as the primary drivers of water level fluctuations in Lake Huron-Michigan. Evaporation strongly influences the annual water level fluctuations, whereas runoff and precipitation covary with the water levels in both intraannual and interannual cycles. Specifically, analysis of phase differences indicated that runoff leads water level change by π/4 rad from 2-month up to 1.5-year cycles, then runoff starts to become nearly in-phase (with small intermittent lags) up to the 12-year cycle, two main recurring cycles of 0.5- and 1-year. Finally, we conducted a comprehensive assessment of 16,809 regression models, which highlighted the effects of runoff-minus-evaporation in modulating the extreme high or low water levels, which in turn could inundate the areas close to the shoreline or reduce the navigability in shallow parts of Lake Huron-Michigan.