The US Army Corps of Engineers and Environment and Climate Change Canada have been coordinating Great Lakes water level forecasts for decades. Six-month forecasts from this partnership are published in the Detroit District’s popular Monthly Bulletin of Great Lakes Water Levels and the Canadian Hydrographic Service's Monthly Water Levels Bulletin. In addition, several other forecast products have been developed by the Army Corps in recent years.
Water level forecasts are produced by first forecasting the net basin supply of water (NBS) to each of the lakes. NBS is the total supply of water, excluding inflows and outflows through connecting channels (i.e., precipitation over the lake plus runoff into the lake from the land minus evaporation from the lake). The Army Corps forecasts NBS using a variety of models.
The IJC’s Great Lakes boards use the joint Canada-US water level forecasts for planning and other purposes. The recent new modeling tools have been developed for application to seasonal water supply and water level forecasts.
For example, the Great Lakes Seasonal Climate Forecast Tool, developed by the US National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory, is a web product that allows a user to view projections of monthly air temperature and precipitation extending seven months, compiled from the North American Multi Model Ensemble, an experimental seasonal forecasting system consisting of models from multiple US and Canadian modeling centers.
Another more recently developed tool is a long-term, experimental forecast of water levels going out five years. This product includes two versions plotted on the same graphic for the sake of comparison.
The two forecasts, and their associated uncertainties, can be thought of as scenarios. One forecast scenario depicts water levels that would result from NBS values drawn from the historical record (i.e., climatology). The other depicts water levels that would result from initial basin conditions and forecasted NBS supplies that have been adjusted using seasonal climate outlooks.
These forecast graphics offer a valuable lesson in the uncertainty in water level forecasts resulting from variability in NBS.
Finally, a Water Level Outlook product developed by the Detroit District describes potential water level outcomes under various scenarios that are of topical interest at the time of the release of the outlook. The scenarios for the Water Level Outlook are updated on a quarterly basis, and graphics are updated each month. For the most up-to-date publication, visit the Water Level Outlook website.