On August 4, 2014, Burlington was struck by a severe storm: over two months of rain fell onto a narrow geographical area. The storm generated significant runoff in a short period of time (flash flood) which flooded homes, businesses and parks, overtopped watercourse crossings, closed roads and also flooded motor vehicles. Homes were flooded by runoff that entered the buildings through the sanitary/storm sewer system, and from runoff that overflowed watercourse banks. Meanwhile in other parts of Burlington just minutes away, the storm was far less intense and people in nearby communities like Hamilton and Milton were enjoying a clear, sunny holiday Monday. Approximately 6,000 properties were flooded within the City during the August 4, 2014 event, roughly 3,500 of which reported basement flooding.
Conservation authorities and scientists often use the term ‘100-year storm’ to characterize events like the August 4, 2014 storm in Burlington. A ‘100-year storm’ doesn’t mean what you may think it does: that a storm will appear once every one hundred years. When Conservation Authorities and others refer to a ‘100-year’ storm, they actually mean a severe storm which has a 1% chance of occurring in any given year. To illustrate, it’s like throwing a one hundred faced die with the storm on just one side: there is always a chance that you could roll the ‘100-year’storm, but it’s a very small chance. Yet, there is also the chance that you could roll that same side or storm twice in a row.
Climate change and the resulting change in weather patterns complicates things because of how engineers and scientists determine the classification of a 100-year storm event. It is determined based on statistical analyses that are in part dependant on storm events that have happened in the past. While global warming is believed to be causing drought and unusually hot temperatures, it is predicted that it may also result in severe storms occurring more frequently. As such, models based on past storm events may not be a reliable predictor of the frequency or intensity of storms in the future. For example, a storm even that is considered equivalent to a 100-year storm based on historical data may end up being a 50-year storm in the future. Or in other words, a storm that might have had a 1% chance of occurring in any given year could now have a 2% chance of occurring. That may not sound like a significant change but ask anyone affected by the August 4th storm event and they will likely say that any potential for that event to occur more frequently is concerning.
The question then becomes how do we prepare our communities from a flooding perspective in light of climate change. One place to focus on is improved flood forecasting and warning, including enhanced data collection and analysis.
To measure rainfall in real-time, a rain gauge network has been established across Conservation Halton’s jurisdiction. However, localized intense storms such as the August 4th event, which was elliptically shaped with a length of approximately 25 km and a width of approximately 9 km, can pass between existing gauge locations making them difficult to detect and monitor. Moving forward, it’s important to continue to enhance the watershed monitoring network by adding more real-time rain gauges in both urban and rural areas to increase coverage and eliminate existing gaps. Integration of existing rain gauge stations operated separately by local municipalities and Halton Region, as well as neighbouring conservation authorities, will also enhance the ability to identify severe storms earlier and more accurately monitor rainfall intensities as they pass through the watershed.
Conservation Halton is also pursuing new technologies and products that are now becoming available to further assist with emergency response. For example, the use of predictive radar products will allow us to assess the potential path of severe storms across the watershed several hours into the future. “Using potential rainfall information generated from predictive radar as input into our watershed hydrology models will enable us to better predict potential locations and the magnitude of flooding within our jurisdiction. This will result in improvements in lead time and accuracy of information contained in our flood messages that are issued to local emergency responders,” says Glenn Farmer, who as Coordinator of Flood Forecasting and Operations at Conservation Halton is leading the initiatives to modernize the Flood Forecasting and Warning program. Mr. Farmer recognizes the importance of a comprehensive watershed monitoring network in order to better predict potential flooding events, provide greater details to emergency responders during severe storm events, and improve post-event analyses and documentation. Accordingly, Conservation Halton is working closely with local municipalities, Halton Region and other partners to develop an integrated real-time data acquisition, storage, analyses and reporting system that will be accessible through the Internet. “The ultimate goal of these enhancements and modernization initiatives is to continue to improve and adapt our systems to maintain flood preparedness and the ability to respond to changing climate and weather patterns observed across our jurisdiction”.
In conjunction with improvements to the Flood Forecasting and Warning program, it is also important to update policies, guidelines, regulations etc., as necessary, to better plan and protect our communities. To this end, Conservation Halton has identified in our Draft Strategic Plan, Metamorphosis, the importance of collaborating with our partners to develop a climate change strategy, and to build climate change mitigation and adaptation into management decisions and activities. Stay tuned as we move forward on this important initiative.
Contributions from: Glenn Farmer, Coordinator of Flood Forecasting and Operations, and Norm Miller, Manager of Communication Services
Special thanks to Janette Brenner and Janelle Weppler for their expertise and consultation.
Last modified: September 5, 2017