| The water levels of Lakes Michigan and Huron have been monitored since 1865, and attempts have since been made to connect their interannual variations to potentially predictable large-scale climate modes. In the present study, spectral analysis revealed 8-yr and 12-yr lake-level cycles, whose periods are similar to those previously identified in atmospheric and oceanic indices in the North Atlantic region. The 8-yr cycle appears to be stemming from changes in daily wintertime precipitation amounts, which result from large-scale atmospheric flow anomalies that affect moisture availability. The 12-yr cycle is most likely resulting from changes in the daily frequency of summertime convective precipitation, due to a preferred upper-air trough pattern that is situated over the Great Lakes' basin. We further analyzed the lake levels after removing outflow-related damping effects, revealing a large ∼80-yr oscillation which is likely connected to the Atlantic Multidecadal Oscillation (AMO).;We have established that the lake-level fluctuations prior to 1980 were predominately driven by changes in precipitation with virtually no time lag. However, we have now determined that for the first time in our years of record, increasing evaporation, which is likely linked to anthropogenic climate change, has begun to significantly affect the lake-levels. Summertime evaporation rates have more than doubled since 1980 as a result of increasing water-surface temperatures and subsequent increases in over-lake wind speeds. The summertime water-surface temperatures are significantly correlated with decreasing wintertime ice cover, and are most likely influenced by the cumulative effect of an increasing number of summertime warming days. |
