Abstract
Great Lakes water levels have been trending downwards throughout the 20th and into the 21st Centuries. Potential causes are numerous. There have been dredging and water diversion projects over the last 110 years, increasing demand for fresh water consumption from a rising population, and considerable variations in environmental factors (rainfall, snowfall, air temperature and wind), all causal in nature. A thorough assessment of United States federal agency and laboratory data archives of time series of winds, air temperatures, rainfall and snowfall, and water level data, reveals that falling lake levels can be linked to rising air temperatures. Non-uniform, post-glacial, isostatic adjustments of the entire Great Lakes region has further complicated the system as land mass tilting causes localized uplift or subsidence that has also altered relative water levels. A mathematical decomposition of the various data sets and accessory calculations strongly indicate regional atmospheric temperature increases over the entire 20th century and the early 21st century resulting in increased evaporation, is the dominant driving factor in the continued downward trend of water levels in the Great Lakes. Moreover, a high degree of correlation was discovered in comparing water level in the Great Lakes with the comparable temporal variability and record length trends evident both the Global (Land and Ocean) Surface Temperature Anomaly time series and the Atlantic Multi-Decadal Oscillation. It is of note that there have been several water level events since 2013 from which the long term losses of fresh water have undergone a change and the lakes have gained fresh water. This received a great deal of attention in both the public press and a scientific newsletter and shows that there is a danger in only dealing with a small portion, 2 years, of a 120 year climate record.
Highlights
The Great Lakes Basin (Figure 1) is home to approximately 40 million people
In order to look at the data more thoroughly, we examine the annual values by month over all years of observations of snow accumulation, rainfall, air temperature, winds and water level for the Lake Michigan domain
These facts strongly suggest that 1 or 2 or even 5 years of persistently high annualized water levels can be a sign of a resurgence of Great Lakes water levels, but in the grand scheme of water level temporal variability, these are short term changes and the overall trends may still be downward
Summary
The Great Lakes Basin (Figure 1) is home to approximately 40 million people. The combined 4,500 miles of United States (U.S) Great Lakes coastline is greater than the combined length of coastline for U.S coasts in Atlantic, Gulf and Pacific and provides important commercial, residential and recreational uses [1] and for hydropower, agricultural irrigation and fisheries [2], within estimated net worth in the hundreds of billions of dollars annually [3]. The eight Great Lakes States (the GLS) entered into a Consent Decree in 1967 regulating the diversion of Lake Michigan water into the Chicago River. At the rate of withdrawal of fresh water from Lake Michigan, and given the lake’s surface area of approximately 57,955 Km2, that withdrawal would result in an annual drop of ~ 4.2 cm per year. As this has been occurring since at least 1967, a period of 46 years up through 2012, this would have amounted to a net drop of 192.8 cm in lake level. Not just outputs should be considered and Received January 19, 2016; Accepted January 25, 2016; Published January 30, 2016
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