Great Lakes Water Levels: Decomposing Time Series for Attribution

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 the National Ocean and Atmospheric Administration (NOAA) National Center for Environmental Information (NCEI) and the NOAA National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) — Reanalysis Project (RP) 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. Nonuniform, 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, appears to be 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 (GSTA) time series and the Atlantic Multidecadal Oscillation (the AMO). 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 presents an apparent quandary to our nearly 120 year, record length study which revealed downward trends in water levels. To wit, this recent upward movement begs the question: Is the two-year change a precursor to increases in water levels or is it just a local blip? We will focus on data up to 2013, but comment upon recently reported increases as part of our analyses.