The Impact of Rising Winter Temperature and Lake-Effect Snow on Streamflow in the Great Lakes Basin, USA

Winter temperature is rising and lake-effect snowfall is intensifying in the Great Lakes Basin, USA. To understand the impact of rising winter temperature and intensifying lake-effect snowfall on streamflow, samples have been collected since 2022 from precipitation, stream water at several catchments, wetlands, and groundwater at varying locations and depths. Samples were analyzed for stable isotopes and calculated for d-excess (δ²H – 8×δ¹⁸O). The mean values of δ¹⁸O, δ²H, and d-excess in precipitation were distinct over summer rainfall (July-September), dormant season rainfall (October-November, May-June), late spring snowfall (March-April), and January-February snowfall dominated by lake-effects. For instance, the mean δ¹⁸O and d-excess values (±1s), respectively, changed from -9.37(±2.54)‰ and 10.03(±5.05)‰  in summer rainfall to -23.54(±2.92)‰ and 31.66(±13.61)‰ in lake-effect dominated snowfall. The mean d-excess values in precipitation over the four periods were significantly correlated (p < 0.05) with both δ¹⁸O and δ²H, decreasing with an enrichment in both δ¹⁸O and δ²H at a rate of -1.38‰ per 1‰ of δ¹⁸O and -0.18‰ per 1‰ of δ²H. The temporal variation of δ¹⁸O, δ²H, and d-excess values in stream water and groundwater were strongly dampened, suggesting longer transit times and mixing with other source waters such as groundwater and subsurface water from wetlands. A mixing diagram, established by δ¹⁸O and d-excess, indicated, surprisingly, that stream water and groundwater were dominated by summer and dormant season rainfalls. However, both isotopes and d-excess values showed that streamflow during winter (December-February) was strongly affected by snowmelt, demonstrating an increasing impact of snowmelt on streamflow during winter. Hydrology and concomitant ecosystem in winter are facing a shift to early spring in the Great Lakes Basin.