Forecasts Surge Ahead with New System

Atlantic Canada averages one or two major storm surges (0.6 metres or more, coinciding with a high tide) a year. Most occur during the winter months, when storms tend to be worse than at other times of the year. Geographical conditions make some areas—including the Gulf of St. Lawrence and the Northumberland Strait—more prone to surges or their effects; however, any exposed coastal shoreline could be affected. This winter, forecasters in the Atlantic Region of Environment Canada’s Meteorological Service of Canada (MSC) implemented the nation’s first fully operational system for predicting storm surges and determining whether they pose a risk of flooding.

The system has been developed and tested in Halifax in cooperation with the Atlantic Environmental Prediction Research Initiative—a collaborative effort involving MSC’s Atmospheric and Climate Science Directorate and the Oceanography Department at Dalhousie University. Researchers at Dalhousie spent more than five years creating a numerical model that predicts surges using data on atmospheric surface pressure and winds on the Atlantic Ocean. The data are provided by MSC’s regional weather forecast model, and enable storm-surge forecasts to be made 48 hours in advance.

The system began running in test mode at the Maritimes Weather Centre in Dartmouth, Nova Scotia, in the fall of 1999. Evaluations carried out by comparing predictions with observed storm surges at a variety of sites proved the system quite accurate, and capable of predicting the magnitude of significant surges—including the one on January 21—to within 10 per cent. In December 2000, it was put into full use for daily forecasting in the region.

Forecasters use daily surge-level maps produced by the system and their knowledge of local geography and tidal conditions to determine which areas of the Atlantic coast are most likely to be affected by surges. They recently added this information to the storm-surge prediction model to create an alert system that automatically warns them when water levels may exceed predetermined site-specific thresholds related to levels of flood damage. The new system was put to the test on February 6, 2001, when stage-one thresholds (the lowest of three) were forecast to be exceeded in some parts of PEI and eastern New Brunswick. Forecasters alerted the provincial Emergency Measures Office in Charlottetown, which monitored the situation and was able to provide sufficient advance notice that merchandise in several retail shops was protected from water damage.

The storm-surge prediction system is also currently being used in a case study on climate-change impacts and adaptation needs for PEI. One of the predicted impacts of climate change is an increase in average global temperatures—a phenomenon that would cause sea levels to rise due to thermal expansion and the melting of polar ice caps. Since the earth’s crust is gradually subsiding in Atlantic Canada, coastal areas in the region will be lower in relation to the base sea level and, therefore, more susceptible to flooding. Meteorologists also say that climate change could increase the frequency and severity of storms, which, combined with higher sea levels, could mean greater potential for damaging storm surges. In addition to using the prediction system to extrapolate future scenarios, researchers are looking at archival data for evidence of emerging trends.

The meteorologists are preparing a scientific paper on the storm-surge prediction system which they hope will be ready for publication in a scientific journal later this year. They will also present their report on the PEI climate-change case study at a public meeting to be held in Charlottetown in September 2001.

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