|Fort McMurray Historical Ice Jam Events|
Recent flooding in Fort McMurray, Alberta highlights how devastating flooding can be, causing widespread damage and even loss of life. Often flood risks are long-standing and challenging to address. For example, Fort McMurray flooding has been affected by ice jams since 1875, based on Review of flood stage frequency estimates for the City of Fort McMurray: Final report by
Alberta Environmental Protection, Technical Services and Monitoring Division (https://era.library.ualberta.ca/items/f6f26d4e-005d-462b-8d7c-0428db8f7d27).
In order to effectively manage flood risks, it is important to understand the causes. Understanding if flood risks are increasing and if current management practices are working to prevent or mitigate risks is important.
Often journalists focus on changes in weather and climate as the primary cause of flooding, or increased flood damages. In fact, historical land use practices and development that began in high risk areas a century before modern flood hazard mapping explains baseline flooding in many parts of Canada. Redevelopment and intensification in these hazard areas can lead to increasing damages over time. Stay tuned for a future post with some examples.
Recently the CBC Ombudsman reviewed how CBC journalists report on past, present and future changes in extreme weather related to flooding in its In Our Backyard series, initiated last summer. The full review is here: https://cbc.radio-canada.ca/en/ombudsman/reviews/Past-Present-or-Future.
What did the Ombudsman find? Well, that "It would have been wrong to state categorically that Canada has already seen an increase in extreme rainfall events", recognizing that has already been reviewed in detail by CBC Radio-Canada Ombudsman Guy Gendron: https://site-cbc.radio-canada.ca/documents/ombuds/reviews/Review%20Robert%20Muir.pdf
The Ombudsman also found that "journalists could have been clearer with their choice of tenses". He
pointed to CBC reporting showing that changes in extreme precipitation are predicted in the future, but have not occurred already from past to present:
"The key stories make no direct claims, for instance, that more severe storms have been observed in Canada. What I saw was often a real effort made to lay out the issues with broad strokes, and avoid getting bogged down in details. Take this excerpt, for example, from the Harrison column:
According to the federal government's recent assessment, Canada's Changing Climate Report, there is "high confidence" that:
- Canada is warming at twice the global rate, and our north is warming at three times that rate.
- We can expect more extreme heat, warmer winters, earlier springs and rising sea levels.
- Precipitation will increase in much of the country.
- Weather extremes will intensify.
The last two bullet points are careful to use the future tense. If, as it appears, Mr. Harrison was the architect of this series, there’s no sense of an attempt to mislead, change facts or distort reality. There are appropriate distinctions made between observed phenomena and predicted phenomena."
So this is positive that CBC recognized the difference between observed phenomena and predicted ones.
While the Ombudsman got it right - more severe storms have not been observed - recent "In Our Backyard" reporting at CBC has already mixed up observations and predictions on this topic. The Flooding tab in this report https://www.cbc.ca/news2/interactives/inourbackyard/ presents the following:
CBC states that extreme rainfall that had a 50 year recurrence time is now happening every 35 years., implying an observed phenomena. What report is CBC referring to? It is Canada's Changing Climate Report: https://changingclimate.ca/CCCR2019/chapter/4-0/
Specifically, Section 18.104.22.168 Projected changes and uncertainties includes a chart Figure 4.20 b) with simulation model projections. Here it is:
The red line representing extreme 50-year storm events has model simulations from past to present to future, showing a predicted decreasing recurrence time (often called a "return period", the inverse of the storm's annual probability of being exceeded).
Obviously the CBC can do better in terms of getting some basic details right - it may even be worthwhile getting "bogged down" in important details like the difference between observed and predicted changes in the factors affecting flooding. As the Ombudsman wrote, there is a need to avoid 'shortcuts' that create 'ambiguity':
"I am not prepared to conclude that this was a violation of policy, but rather as a reminder that there cannot be shortcuts in language if they create ambiguity. This is a particular challenge in broadcast, where being concise is so critical, but editors and reporters should not leave out any word if it is necessary to sharpen the clarity of the reporting. When CBC is referring to the future, it would be better to say so. That way viewers won’t be left guessing."
Mixing up past, present and future continues to create ambiguity, leaving CBC viewers misinformed about actual extreme storm trends. Unfortunately, this can divert attention from the other factors that affect flooding and that should be given our attention when managing long-standing risks.