4. Conclusions
This study assesses trends of year-over-year variability in both observed Laurentian Great Lake levels and net basin supply components. Our analysis found definitive statistical evidence of robustly increasing interannual variability in both the levels of individual Great Lakes – outside of well-regulated Lake Ontario – as well as in the individual hydrologic components of lake levels across all basins. These rises in variability coincide with a period of observed intensification of the hydrologic cycle due to anthropogenic-driven changes in climate (IPCC, 2021). Other potential factors contributing to the trends we observe here include changes in precipitation caused by evolving aerosol concentrations, changes in land use and urbanization, shifts in historical measurement availability and accuracy, and, in the case of lake level variability, changes in water level management and regulation (REF). Regardless of cause, our characterization of trends in interannual variability necessitates future work to determine if these increasing trends in hydrologic variability will persist in future climate states, as well as how this shift in the physical climate system will impact society and the environment.