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Increasing evaporation and precipitation are offsetting, except on Superior

The Study sought to improve the accuracy and consistency in net basin supply (NBS) estimates through modification of existing models, development of new models, collection of new data, and improvement of a range of methodologies that have been used for lake level estimation. It was concluded that the improved estimates of runoff, evaporation and over-lake precipitation still incorporate and introduce significant uncertainty into the overall water balance. Despite uncertainties, the Study concluded that it is clear that lake evaporation is increasing and likely will increase for the foreseeable future, likely due to the lack of ice-cover, increasing surface water temperatures and wind speeds. Analysis indicates that in the Lake Michigan-Huron basin, this increased evaporation is being largely offset by increases in local precipitation. In the Lake Superior basin, however, increasing evaporation over the past 60 years has not been compensated for by increased precipitation. As a result, NBS have been declining in general in the basin. This trend is consistent with the current understanding of climate change. Unless changes in the precipitation regime occur, which is possible, NBS in Lake Superior will continue to decline, on average, despite the possibility of higher water supplies at times. It will be important to ensure that further climate analysis be undertaken to explore these dynamics and provide more certainty of future NBS estimates.
Related Projects
GLERL Component NBS
Direct Observations of Evaporation
MESH Component NBS
Closing the Water Balance using MESH
Closing the Water Balance using Adjusted GLERL Data
Hydroclimate Synthesis and Summary