Study finds ‘Goldilocks’ resolution for presenting flood risks on large-scale models

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A new study claims to have found that moving from a low resolution to an optimal resolution for presenting flood risk information on large-scale models increases the accuracy of the flood risk to neighbourhoods and individual properties as frequency increases and claims costs rise.

Coordinated by the Canadian Water Network (CWN) and the Insurance Bureau of Canada (IBC), the study, Improving Flood Risk Evaluation through Cross-Sector Sharing of Richer Data, shows that large-scale flood risk models often rely on topographical data views at 30 metres, when 5-metre grid spacing would provide the optimal resolution to evaluate flooding from intense rain events.

“A dense dataset is likely too costly and impractical to produce national-scale pluvial flood maps,” the study states. “A 5-metre grid spacing reduces processing time, with minimal reduction in output quality as compared to finer grid spacing. However, it may be advantageous to use 2-metre grid spacing in certain key areas, such as dense urban centres,” the study adds.

To determine the optimal resolution, the study coordinators partnered with two renowned global flood risk-modelling firms and five municipalities. They found that when comparing the two types of data inputs (i.e., topographic and flood defense measures), the “greatest improvement resulted from the incorporation of higher resolution topographic data from a reliable origin, such as LiDAR-based technologies.”

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The study also found that large-scale flood risk models should give greater consideration to flood mitigation infrastructure or defense measures that have been implemented by Canadian municipalities.

Property and casualty insurance payouts from extreme weather have more than doubled every five to 10 years since the 1980s. Flooding now costs Canadians more than any other climate issue, representing 36.8% of all insurance claims for the Canadian insurance sector.

“The study’s conclusions are important for insurers wanting to expand flood coverage for consumers, particularly in areas identified as high risk on traditional flood hazard maps,” said Craig Stewart, Vice President of federal affairs at IBC, in a statement. “Improving access to richer information is a significant opportunity for Canadian municipalities, insurers and homeowners to better understand flood risk and to take action.”

Stewart added that IBC is also calling on governments to immediately invest in improving the quality of terrain data and make that data available for property owners to identify their exposure to flooding.

IBC says the results bolster its position that governments should target priority infrastructure investments in the areas at highest risk of flooding to protect as many people as cost-effectively as possible.

The study’s conclusions support IBC’s position on the need for a National Action Plan on Flooding.

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