Projecting Future Water Availability in the Great Lakes Megalopolis: Reconstructing Lake Michigan-Huron Lake Level and Regional Hydroclimate Using Tree Rings

Abstract:

The ability to accurately predict water availability in the cities surrounding Lake Michigan-Huron becomes particularly difficult when the uncertain effects of climate change, such as changes in precipitation patterns and evaporation rates, are considered. Lake level reconstructions provide useful model inputs to better predict this availability. Annual tree-ring widths have been successfully utilized in reconstructions of lake levels in the Great Lakes region via the creation of proxy datasets of temperature and precipitation that are then input into a multilinear regression model to reconstruct annual average lake level. Here, the combination of this approach with analysis of instrumental records of precipitation and stream flow input allows for a more comprehensive understanding of regional hydroclimate and improved projection of future water resource availability. Annual tree-ring widths of cores collected from four old-growth forests near southern Lake Michigan were combined with over 30 archived tree-ring width chronologies from the Great Lakes region and used to create proxy datasets of temperature and precipitation. A multilinear regression model related these proxy variables to Lake Michigan-Huron lake level and stream flow of the Saint Clair River, which flows into Lake Michigan-Huron, for the period of available instrumental record (1860-present). When possible, the available tree-ring widths were used to reconstruct these variables for years prior to the instrumental record. Timing and severity of rainfall events were also analyzed to identify spatial and temporal patterns and their variability over time. The combination of updated tree-ring width chronologies, chronologies from newly sampled sites, and instrumental records of various indicators of water availability provides novel and valuable insight into the future lake level of Lake Michigan-Huron.