Forecasting Water Levels

Forecasting Water Levels – General Overview

By David Sweetnam, Executive Director of Georgian Bay Forever (Last updated December 2020)

Water levels are the visual result of the sum total of all inflowing and outflowing water to a water body such as those of our Great Lakes. This sum total is referred to as the total net basin supply. Historically water levels followed the precipitation as the major determinant, but from roughly the 1990s to 2014, that changed towards evaporation, of which there were few ways of measuring properly. More recently, there is more increased precipitation and longer wet seasons including the last 3 years where some records were broken. As the two major water levels determinants, the balance between evaporation and precipitation is what is determining where the water levels will go in the future.
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<p style=On a day-to-day basis the weather is what we see when we look out the window. In the near-term we can forecast water levels conditions based upon the things that impact our weather like the jet stream, and ocean circulation patterns such as El Niño and La Niña. This forecast is accurate at the time it is issued but increasingly uncertain as it looks into the future. In general, these forecasts are only useful when looking into the future to a maximum of six months at which time the uncertainty in the forecast becomes so large that the forecast is no longer meaningful.

The long term (thirty or forty years) trends are what establish the climatic conditions. It is changes in the energies in the atmosphere that are changing our climate. Global heating is resulting from the human activities that increase “green-house” gasses such a carbon dioxide, nitrous oxide, methane and others that we are dumping into our atmosphere. These gasses inhibit the radiative heat loss the planet experienced in its normal state.

What we know about the future climatic conditions is that this increasing energy in our atmosphere is causing changes in precipitation and evaporation – both expected to increase and become more intense and variable according to present models. This increasing flashiness that we are seeing today is expected to increase the extreme water levels conditions (both extreme highs and extreme lows) and the speed of transitions of water levels between those extremes leading to increasing water levels variability in the coming decades.
Predicting future water levels in this new climate regime is done using modelling systems. These models can’t predict a specific water level on a specific future date, but they can predict a range of water levels with a specified confidence range; for example, models can say that average water levels will be 15 centimetres higher than today’s average and range between one metre above or below that average level ninety-five percent of the time.

This is known scientifically as the 95th percent confidence interval. If we report the 50th percent confidence interval it means that we would expect the water levels to be within that range half the time.
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Water levels also lead to a variety of challenges at both the high and low ends of their range. For example at high levels properties may be flooded and fixed structures such as docks and boathouses may be damaged by wave action. At low water levels there may be increasing navigational hazards from rocks and shallow water or undercutting of shoreline hardening structures or shoreline bluff “toes” by wave action that will result in bluff erosion when water levels return to average or high conditions. These impacts depend on the shoreline type and the conditions it experiences. In some cases these processes are natural but impacted by increasing energies induced into the system by human induced global warming.

This all means that there is a judgement call pertaining to acceptable risk involved by property owners or governments when investing in infrastructure as to what the cost-benefit is to any decisions influenced by water levels. Some properties’ topographies might afford owners to site buildings and infrastructure such that these increasing fluctuations and highs and lows do not adversely impact their investments. Some investments might be made to accommodate these increasing ranges by installing floating dock and boathouses and in some cases cottages. It is a matter of determining what the likely ranges of water levels and what the resulting wave energies will do and then designing infrastructure to withstand those conditions and energies. For example, in the Bay of Fundy there are 40-foot tidal conditions that happen twice daily and do not adversely impact boats and docks because they are expected and have been designed around.

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Current Water Level Conditions and Forecasts

- The USACE weekly Georgian Bay (Lake Michigan-Huron) water levels: click here.
- The USACE monthly Georgian Bay (Lake Michigan-Huron) water levels: click here.
-LEVELnews: monitoring Great Lakes and St. Lawrence River water levels, From the Government of Canada. Click here.
-The 12 month outlook summary for the Great Lakes in English units.

These forecasts are issued by the USACE in coordination with the governments of the US and Canada.

Hydrologic cycle

What is the water level forecast for the next five years?

Increasing variability and flashiness with a slight trend to higher average levels and wider range between highs and lows.

CHECK out this January 12th, 2021 article featuring David Sweetnam, GBF's Executive Director, and Dr. Andrew Gronewold with the School for Environment and Sustainability at the University of Michigan.
CLICK HERE for, "Climate change clear driver of Lake Huron's high water, long-term forecast uncertain"

GBF Was asked? As a long-time resident of the Bay, I have witnessed these cycles, obviously there is a scientific root cause analysis?


There are no discernable periodic cycles. By this we mean that there is no discernable seven or 15 or 20 or any regular yearly cycles that water levels follow. Water levels do fluctuate but these fluctuations are chaotic. Climatologists look at patterns that might emerge across spans of 30 or 40 years. The past observed fluctuations existed within a climate regime that is no longer present. This is true for traditional knowledge holders and western science record keepers. The new regime will continue to change and has resulted in changes to the way that major water level components such as evaporation and precipitation interact. We expect to see the range of water levels increase beyond their historic range, with the extreme levels increasing and decreasing at high and low levels respectively, and the speed of transitions between water levels increasing, as we experienced in 2014 when water levels rose from an extreme low to an extreme high faster than ever before recorded.