Causes of variability in monthly Great Lakes water supplies and lake levels

Abstract

The purpose of this study was to identify those water budget components of the Great Lakes that have most frequently been a major cause of anomalous net basin supplies (NBS) and of rising and falling lake levels at the monthly time scale. Principal component analysis and a simple counting of relative frequencies revealed that on the upper lakes NBS anomalies are most sensitive to overlake precipitation, but on the lower lakes they are most sensitive to runoff. This shift is due to a downstream increase in the magnitude and variability of runoff. Evaporation variability plays a larger role in the NBS of the upper than the lower lakes and is most important during dry months. During wet months evaporation is not as much suppressed as one might assume from the simple cloud cover/insolation/temperature/evaporation relationship; this is most likely due to an increase in wind speed. High and rising as well as low and falling lake levels are the result of anomalous NBS on all lakes and represent condition beyond the capabilities of lake-level regulations. Changing conditions -low but rising levels or high but falling levels -are the result of anomalous NBS for all of the lakes except Ontario, for which almost all such changes are achieved by regulating the outflow.

Remote Sensing of the North American Laurentian Great Lakes’ Surface Temperature

“…An early spring thaw leads to a late winter freeze-up, creating a positive feedback loop [1,36]. Studies have shown that changing climate has resulted in decreased ice cover over the Great Lakes [4,[37][38][39][40]. Now, this study is also finding that the changes in the ice cover themselves have an impact on the Great Lakes' hydro-climate and thermal stratification as a whole.…”

Connecting past and present climate variability to the water levels of Lakes Michigan and Huron

“…It was recently determined that long‐term lake level fluctuations were primarily resulting from changes in precipitation [ Brinkmann , 2000; Hanrahan et al , 2009], and since the pre‐1980 interannual variation of evaporation was relatively small, it had little effect on long‐term lake level variations. Over the last few decades however, evaporation rates have begun to increase, resulting in decreasing lake levels despite continued above‐average precipitation totals.…”

Quasi-periodic decadal cycles in levels of lakes Michigan and Huron

“…a2. Probability Density Function (PDF) of time intervals between consecutive lakelevel maxima based on ridge data for Baileys Harbor only (Thompson and Baedke, 1997, 2000 (solid black line). Dashed lines show the 95% confidence interval associated with red-noise null hypothesis (see text).…”