A recent article in the Canadian Journal of Water Resources offers a discussion of flooding and how a new approach is required to help mitigate the increasingly fatal risks.

Authors Matthias Jakob and Mike Church explain that river and coastal floods, in an average year, kill over 25,000, affect 520 million people, and render 3.2 million homeless, with an annual cost to the world economy of $60 billion US dollars. In Canada, we spent $2 billion on damages from flooding in the 20th century.

The article states that “flood management aims to reduce harmful impacts to people, the environment and the economy of a flood-prone area, and “risk” combines consideration of the flood hazard and its consequences. But those consequences are not all, or at least, not systematically quantified and so full appreciation of flood risk remains, in most instances, unknown.”

The Canadian approach to flood hazard management to date has largely focused on the “design flood,” a concept that serves as the foundation of design public infrastructure and flood protection.  The design return period, which provides scientists with a sense of the discharge, is fixed. As discussed in the ACT Water Climate Change Adaptation and Water Governance report, climate changes mean that we are now dealing with a loss of stationarity – i.e. extreme weather that is extending well outside the coping range humans have established as the best and worst case scenarios we have to manage.

As a result of this fixed “design return period” based on historical data that is fast becoming obsolete, both flood plain development, and flood risk itself, have simultaneously increased, posing greater risks.

The authors call for continuous risk-based adjustment of flood response approaches that balances the long term changes in risk associated with flooding levels (see Figure 2 in the paper). Some European countries are moving to a risk-based flood management approach, which is an alternative to the hazard-based approach that we currently use in Canada.

Called the Quantitative Flood Risk Assessment (QFRA), this approach evaluates the likelihood and consequences of flooding and reflects possible combined contributions to flood risk of various operational and hydrologic factors. The risk-based approach differs from the hazard-based in that it offers ways to identify locations of high risk that occur due to increases in the vulnerabilities and consequences of a flood. This approach can also help decision-makers evaluate other flood mitigation alternatives, and define thresholds for the tolerance of flood risk.

A number of studies are currently underway in British Columbia to better understand the potential benefits of QFRA.

A key message from an international symposium on flood defence held in Toronto May 2008 stated that appropriate investment to reduce flood risk, and the use of resources for flood disaster prevention, offers significant economic benefits, and will save numerous lives, prevent property damage and promote social stability.

The article by Jakob and Church also validates ACT’s 2009 report on Climate Change Adaptation and Extreme Weather [PDF]. Recommendation 3 of this report calls for local governments to assess both their current vulnerability to extreme weather (such as floods) and the risks posed by climate change, and use risk management as a framework to prioritize actions targeted at climate-related risks.

Jakob and Church offer recommendations focused on planning and systems adjustments and prevention of flooding, one of which includes a routine inclusion and regular update of analyses of the effects of climate change on the duration, frequency and magnitude of future floods for all high river levels.

Please read the full article for more details.

By ACT water researcher Tim Shah