Observing Changes in the Great Lakes Water Level Variability

The effect of climate change on regional weather patterns and hydrological outcomes remains uncertain. For example, it is uncertain if recent dramatic changes in Laurentian Great Lake water levels are driven by anthropogenic forcing or are the result of natural variability. Each of the individual Great Lakes has recently reached record high levels, and in some cases record highs have followed recent record lows, suggesting a potential shift in hydrologic variability.To assess this potential we investigate the hydrology of the Laurentian Great Lakes system over the past century-plus (1900-2020) using lake water levels compiled by the Great Lakes Coordinating Committee. These data are aggregated from 87 gauges across the Great Lakes-St. Lawrence basin operated by NOAA and the Canadian Hydrographic Service (CHS). Rolling averages of surface elevation for each of the Great Lakes reveal changing standard deviations between the first and second half of the century, which is notably accompanied by recent maxima in standard deviation for all lakes in the basin and statistically significant long-term trends in variability for Lakes Ontario and Superior. These trends are further demonstrated by comparing kernel density on the first and latter halves of lake level data (i.e. 1900-1959, 1960-2020). To determine the role of specific hydrologic components in Great Lake levels, we also incorporate similar analysis of precipitation and evapotranspiration data from the gridded Global Precipitation Climatology Centre (GPCC) and Livneh Daily Observational Hydrometeorology datasets. We investigate the relative importance of precipitation and evapotranspiration, including changes in their annual variability for each catchment basin. Ultimately, our results help to increase understanding of Laurentian Great Lake level variability (and the components thereof) and will prove important in efforts to mitigate increased risk for coastline flooding, shoreline erosion, and transportation and trade impacts. In addition, these findings allow for a historical comparison against predicted regional changes in the hydrologic cycle caused by anthropogenic climate change and may indicate a shifting regime in Great Lake water levels.