We are interested in the variability of lake levels in Minnesota, and the
relationship between lake levels and climate. We analyzed historical water levels in 25
Minnesota lakes. Eight were landlocked lakes and seventeen were flow-through lakes.
The data were daily values, but substantial gaps existed. The longest record reached
back to 1906 (Lake Minnetonka and Upper Prior Lake in Scott County). We determined
statistical parameters such as mean annual lake levels and seasonal variations of the
historical lake water levels. Linear regression and Mann-Kendall test were used to
evaluate the presence of trends in daily, mean annual, spring (May) and fall (October)
The majority of the 25 lakes showed rising water levels in the last century (1906
to 2007). The strongest upward trend was observed in a landlocked lake (Lake Belle
Taine in Hubbard County) where the rate was 0.030 m/yr. The second largest increase
was observed in a flow-through lake (Marion Lake in Dakota County) with a rate of
0.024 m/yr. Swan Lake (in Nicollet County) and Swan Lake (in Itasca County) were the
only lakes that showed a falling trend with a rate of -0.011 and -0.002 m/yr, respectively.
The analysis also showed that lake levels have been increasing in most of the 25
lakes in the last 20-years (1987-2006). One landlocked lake and eight flow-through
lakes showed their strongest upward trends in the last 20 years. Five of the eight
landlocked lakes and eleven of the seventeen flow-through lakes reached their highest
recorded levels after 1990. Upward trends in recorded lake water levels were found in
both spring and fall in the majority of the 25 lakes analyzed.
We also attempted to understand how Minnesota lake levels have responded to
climate changes in the past. Correlation coefficients were calculated between annual
lake water levels and mean annual climate variables. The correlation of water levels
with precipitation was moderate, and the correlation with dew point and air temperatures
was very weak. 48- and 36-month antecedent precipitation was the strongest indicator
of average water levels. Multivariate regression analysis of lake levels did not improve
the lake level predictions. Numerical indicators for ground water and surface water inand
out-flows appear necessary for further improvement.
The correlation between mean annual water levels was strongest among lakes in
the same climate regions and weakest among lakes in distant climate regions. Lake
levels in the same Minnesota climate region (with identical precipitation and
temperatures) had correlation coefficients as high as 0.78, while those in distant regions
were not correlated. The average correlation coefficients among annual water levels in
all lakes were 0.43 for the eight landlocked lakes and 0.41 for the seventeen flowthrough
Overall, the analyses showed that changes have occurred in lake levels in
Minnesota in the last century and in the last 20 years. The majority of the lakes have
rising lake levels. The correlation between climate parameters and lake levels was
weak. The consistency of water level variations in lakes of the same region is perhaps
the strongest indicator of a climate effect. If the trends continue, lakes included in this
study may experience significant water level increase by 2050.
Legislative Citizens Committee on Minnesota Resources
Dadaser-Celik, Filiz; Stefan, Heinz G..
Lake Level Response to Climate in Minnesota.
St. Anthony Falls Laboratory.
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