Background
Larson and Schaetzl (2001) investigate the climate-alarmist contention that "increased evaporation under a possible greenhouse-enhanced climate, coupled with even more consumptive use of the Great Lakes waters, could lead to lower lake levels in the near future," finding, of course, that there is no real-world evidence to support this claim.

What was done
Argyilan and Forman explore the subject in a bit more detail for the Lake Michigan-Huron system, which they say is "the least affected by engineering modifications that influence lake-level" and, hence, should be a "sensitive proxy for understanding the relation between climate and water-level fluctuation within the Great Lakes."

What was learned
The authors report that their "analyses of hydrometeorological data from 1920 to 1995 indicate an increase in summer precipitation [and] greater autumn and winter hydrologic inputs into the Lake Michigan-Huron system."  Specifically, they note that "total water input increased from 1920 to 1995 in autumn and winter at rates of 14.6 and 9.3 mm per decade, respectively," with the rise in autumn input being the result of increasing trends in both overlake precipitation (8.3 mm per decade) and runoff (6.3 mm per decade) and the rise in winter input being the result of a shifting of about 7.5 mm per decade of spring runoff to winter runoff.

What it means
In the face of such measurement-derived trends, one would logically have expected the lake level of the Michigan-Huron system to have been rising over the period of study, rather than falling, as climate alarmists imply it should have done in response to the dramatic global warming they claim to have occurred over this period.  Hence, it should come as no surprise that what the measurements suggest has indeed been the case, i.e., the level of the Lake Michigan-Huron system has risen over the period 1920 to 1995, as is clearly demonstrated by the data presented by the authors, which were adapted from Quinn (2002), as well as the data presented by Larson and Schaetzl (2001).

References
Larson, G. and Schaetzl, R.  2001.  Origin and evolution of the Great Lakes.  Journal of Great Lakes Research 27: 518-546.

Quinn, F.H.  2002.  Secular changes in Great Lakes water level seasonal cycles.  Journal of Great Lakes Research 28: 451-465.