Enhancing total water prediction for the Great Lakes through calibration of the National Water Model in Canadian watersheds

The need for water supply and water level forecasts that are appropriate for use in predicting coastal flooding on the Great Lakes was underscored in 2019, when record high water levels in the Great Lakes resulted in significant damage to property by lakeshore flooding. The Great Lakes are essentially bisected by the border between the United States and Canada, resulting in the need to resolve discontinuous data over a large spatial domain. This discontinuity, along with discontinuity in federal agencies' traditional jurisdictions, has limited the development of models supporting coastal flood forecasts. Over the decades, binational coordination has resulted in the evolution of seasonal forecasts of water levels, provided in the form of the official coordinated 6-month forecast of Great Lakes water levels produced by the U.S. Army Corps of Engineers and Environment and Climate Change Canada. While these forecasts contain useful information for decision-making at seasonal scales, there remains a gap in water supply and water level predictions at the shorter time horizons and finer temporal and spatial resolution required for flood forecasting. Over the past two years, efforts to extend the National Water Model (NWM) hydrofabric and thus forecast coverage for the entire Great Lakes basin have been on-going, resulting in the planned implementation of the Canadian land surface in NWM version 2.1. A significant piece of this effort is the calibration of 27 Canadian watersheds, which utilized the Dynamically Dimensioned Search algorithm through the NWM calibration workflow. Calibration was performed using Analysis of Record for Calibration (AORC) meteorological forcings developed by the National Oceanic and Atmospheric Administration Office of Water Prediction (OWP) over five water years spanning from 2008 to 2013 and the streamflow simulation was evaluated over the next three water years (2013 to 2016). This presentation shares the results of calibration over the Canadian Great Lakes watersheds, as well as regionalization to the non-calibrated basins for NWM version 2.1 implementation.