In plain language, there is no general 'new normal' of bigger or more intense storms that cause flooding in urban areas across the country.
This is in contrast to most of the media reports that have claimed a 'new normal' of torrential storms, even dubbed 'ghost storms' or 'ninja storms'. For example, in Mark Mann's recent story "HELL AND HIGH WATER" in Toronto Life the byline was "Torrential storms have become the new normal. They’re turning our basements into lakes and our streets into rivers. Is Toronto ready for the age of the flood?" (see image below).
Readers of this blog will appreciate that what causes Toronto streets to become rivers during extreme rainfall is old, pre-1980 drainage design standards that did not account for extreme weather in road and lot grading or sizing of sewer infrastructure. Municipal flood reports indicate a high risk of basement flooding in proximity to these under-designed 'lost rivers', as shown in a review of May 2000, August 2005 and July 2013 extreme rain event flood reports (see presentation "Urban Flood Risks from Flood Plain to Floor Drain, Correlation of Basement Flooding With Overland Drainage & Topographic Risk Factors During Severe Storm"). Insurance claim data shows more reported claims in the lost river zones through old communities built with limited extreme weather capacity. Flooding in concentrated in these old communities, with the highest density of flooding in "partially-separated" sewersheds where between 1950 and 1980 many foundation drains and rooftops were conveyed into sanitary sewers that were never designed to handle extreme wet weather inflow and infiltration stresses. This can be shown with data on flooding and monitored extraneous wet-weather flow stresses:
Changes in catchment characteristics and remediation priorities due to CC and level of service upgrades".
3) At the NRC workshop, the high extraneous wet-weather high flow risks in old, partially separated sewer service areas, are shown in the 100-year peak flow rates - for partially-separated sewersheds in Ottawa the rate is 4.87 L/s, which is 850% above the rate for modern, fully-separated sewersheds. Since hydraulics of sewer flow are non-linear, doubling extraneous flow increases friction losses by 4 times. So older sewers can have 8.5-squared or over 70 times the friction losses of newer sewers during a 100 year storm - that helps explain why dwellings serviced by old sewers are more flood-prone.
The Toronto Life article also refers to a recent Toronto flood event saying "The August 2018 squall belonged to a class of storms that are occurring more frequently in Toronto as the climate changes. Sometimes called “ghost storms” or “ninja storms” for their sudden appearances, these extreme downpours possess two qualities that allow them to strike violently and without notice: they’re super-compact and super-localized."
This type of media statement is not supported by any data. In fact, observed maximum rainfall volumes in and around Toronto have been decreasing according to Environment and Climate Change Canada's Engineering Climate Datasets. The most recent Version 3.0 datasets show decreasing observed annual maximum rainfall in Toronto over storm durations of 5 minutes to 24 hours (i.e., "short-duration precipitation" noted in the Minister's letter), as shown below:
For durations of 12 hours, the decreasing trend is statistically significant at Toronto's longest-running climate station with records going back to the 1940's.
Looking at charts across the GTA (see Pearson Airport and Buttonville Airport climate stations in a previous post) we see many similar decreasing trends, and no "new normal" of torrential rain - in fact, the new normal is often less extreme rainfall intensities. Numerous engineering studies (summarized here) have shown no "new normal" either in the region.
The same decreasing trend in the GTA holds true across southern Ontario, where in a previous post the observed annual maximum rainfall trends at 21 long-term climate stations showed 42% more decreasing trends than increasing ones (see summary chart at right). So the Minister's statement on extreme precipitation evidence is certainly a good reflection of data in this region.
In the previous Version 2.3 datasets, a review of annual maximum trends across Canada showed other regions with decreasing overall trends too. This table below counts trends in the short 5-minute duration observed rain intensities in different provinces and territories:
5 Minute Extreme Rainfall Trend
Province Station Count
Trend / Significance
Decrease/ Not Significant
Increase/ Not Significant
Some entire regions have decreasing short-duration trends, as Environment Canada noted in Atmosphere-Ocean in 2014 (Trends in Canadian Short-Duration Extreme Rainfall: Including an Intensity-Duration-Frequency Perspective), "The decreasing regional trends for the 5- to 15-minute duration amounts tend to be located in the St. Lawrence region of southern Quebec and in the Atlantic provinces". Consistent with the Minister's statement on observational evidence, the Atmosphere-Ocean paper stated "single station analysis shows a general lack of a detectable trend signal, at the 5% significance level". There are no "consistent changes" as the Minister notes.
My outreach to the Prime Minister on this topic was following the 2017 Gatineau flooding as described in a previous post. Specifically, given my earlier review of Engineering Climate Datasets' trends and Environment Canada's Atmosphere-Ocean statements, I had asked the PM for any information to support his 2017 statements:
1) "The frequency of extreme weather events is increasing, and that's related to climate change"
2) "We're going to have to understand that bracing for a 100-year storm is maybe going to happen every 10 years. Or every few years."
The PMO did not provide any supporting information on event frequency statements though. It is understandable that some politicians may not be aware of the actual data trends, especially given that the insurance industry has been promoting a "Weather Story" since 2012 whereby extreme weather events were said to have increased in frequency (i.e., 40-year events becoming more frequent 6-year events) - this frequency shift had been widely reported in the media and was even repeated by TD Bank's chief economist - unfortunately, this "Insurance Fact" on event frequency has been shown to be only a theoretical shift, and not based on Environment Canada data as was originally cited. A full review of this substitution of theory for actual observational data is in this presentation Review of Weather Event Statement in Insurance Bureau of Canada’s Telling the Weather Story prepared by Institute for Catastrophic Loss Reduction.
The PMO forwarded my original question to the Minister over a year ago. The response received this week would appear to not support the PM's 2017 statement "The frequency of extreme weather events is increasing".
The Minister's response relies largely on the recent Canada's Changing Climate Report, Chapter 4, pages 117 and 119 (see excerpts at right).
The Minister wrote that there is "not yet" evidence of "consistent changes", perhaps implying that some changes are apparent but not consistent or widespread for extreme precipitation. The cited report implies even less is happening to these extremes, stating "evidence of changes" "is lacking" (no mention of 'consistent' changes).
Global News report related to 2019 spring flooding:
"Environment Minister Catherine McKenna said Thursday that the “one in 100-year flood” is happening much more frequently."
"This flooding is happening here in Quebec, it’s happening in Ontario, it’s happening in New Brunswick. And really sadly, what we thought was one-in-100-year floods are now happening every five years, in this case, every two years,” she said."
There is a potential disconnect between the Minister's statement on lack of evidence of extreme precipitation changes and an increased frequency in 100 year floods. It must be noted that flooding on the Ottawa River, and other large watersheds, is driven by seasonal climate factors like the amount of snowpack accumulated and its melt rate during the spring freshet. Large river flooding is not governed by the short-duration precipitation that affects small, 'flashy', urban watersheds.
Changes in temperature affect snowpack accumulation and winter hydrology. Canada's Changing Climate Report suggests lower snowpack amount along with warming temperatures (see page 118 "As temperatures increase, there will continue to be a shift from snow to rain in the spring
and fall seasons"). Researches at the University of Guelph School of Engineering have suggested that spring peaks have decreased in rural watersheds as a result of warmer temperatures.(see May 2019 report Historical Floods of Ontario: A Reported Flood Event Database and Preliminary Analyses of Variability) The chart below shows decreasing spring peak flows as a result of higher winter runoff and lower spring snowpack in the Moira River watershed:
The Prime Minister's recent statements in 2019 appear to be better aligned with the data than his 2017 statements, suggesting now that changes in extreme weather and flooding are only predicted, but have not yet occurred. For example the PM recently stated "we're going to see more and more of these extreme weather events more regularly. It means we have to think about adaptation, mitigation and how we are going to move forward together." (see HuffPost report). No claim that we are already seeing these extreme weather events is made. That is consistent with the Minister's letter that there are predicted changes.
Recognizing that there is no evidence of changes to date is important. This should in fact influence our mitigation and adaptation priorities, especially given the potentially high cost of mitigation or adaptation measures. The American Society of Civil Engineers (ASCE) has published a manual of practice (Climate-Resilient Infrastructure: Adaptive Design and Risk Management) for adapting infrastructure to account for future risks, as noted in a previous post.
The ASCE guide proposes to classify infrastructure by it's criticality, based on potential loss of life and economic impact as well as the service life of the asset to determine an approach for addressing potential future climate change effects. One of the principles is that given uncertainty with future climate, one may design infrastructure considering today's climate if the risk class is low, or if future adaptation is feasible.
The Minister has recently tweeted that "It is therefore no longer sufficient to rely on historical statistics and past experience to quantify future risks" (see right). The ASCE manual of practice would suggest otherwise for some classes of infrastructure.
The ASCE guide also promotes an approach called the Observational Method (OM), defined as follows:
"The Observational Method [in ground engineering] is a continuous, managed, integrated, process of design, construction control, monitoring and review that enables previously defined modifications to be incorporated during or after construction as appropriate.All these aspects have to be demonstrably robust. The objective is to achieve greater overall economy without compromising safety."
The OM approach has been adapted by ASCE to designing climate resilient infrastructure and has the following steps:
1. Design is based on the most-probable weather or climate condition(s), not the most unfavorable and the most-credible unfavorable deviations from the most-probable conditions are identified.
2. Actions or design modifications are determined in advance for every foreseeable unfavorable weather or climate deviation from the most-probable ones.
3. The project performance is observed over time using preselected variables and the project response to observed changes is assessed.
4. Design and construction modifications (previously identified) can be implemented in response to observed changes to account for changes in risk.
The OM approach is a largely a 'wait and see' approach whereby performance can be monitored over time to determine what modifications have to be made in response to changing risks. Obviously today's known risks, including those related to old infrastructure design standards causing most urban flooding, and high-risk land uses causing most river and shoreline flooding, can be actively addressed today. There is no need to wait there.
There is not, however, any overwhelming need to embank on expensive adaptation strategies, e.g., implementing widespread green infrastructure measures that come at a known high cost, or doubling the size of all infrastructure as if 100-year storms are now already 10-year storms and the runoff stresses on our systems are already drastically bigger. Quite the opposite - the Ontario Ministry of Transportation (MTO) has determined that even with future predicted rainfall intensity increases most sewers, culverts and bridges can handle that runoff. As noted in a previous post, MTO's 2015 report The Resilience of Ontario Highway Drainage Infrastructure to Climate Change stated:
"Based on the analysis of samples of highway infrastructure components there is demonstrated resilience of MTO drainage infrastructure to rainfall increases as a result of predicted climate change scenarios. An overwhelming percentage of the storms sewer networks tested appeared to have sufficient excess capacity to hand the increases in design flow rates up to 30%. Similarly, the sample of highway culverts analysed showed adequate capacities, for a large percentage of the culvert, to handle the rage of low rate increases investigated without the need to be replaced. The bridges tested also appeared to suffer no risk to structures as a result of the flow increases."
This is in direct contrast to media reports that claim in the future all sewers and culverts will be too small. In the TVO article There will be floods — and Ontario’s not ready for them the former Environmental Commissioner Gord Miller states “We have no predictability any more. One has to look from the perspective that all culverts are undersized. All sewers are undersized.” The fact is that we have more long-term records than we ever did showing no change in extremes, and carefully analyzed system hydraulics show no universal undersizing of infrastructure - it is in fact the opposite. The majority of systems are resilient in the future when designed to today's standards. We do still have to upgrade the old systems that were never designed to handle yesterday's, today's or tomorrow's extremes.
The media is unfortunately mischaracterizing many of today's known flood risks and extreme weather damages as being caused by climate change effects. The insurance industry has also claimed that increasing damages are caused by these effects. Clearly if there is no evidence of changes in extreme precipitation, no evidence of 'ghost storms' or 'ninja storms', and so damages cannot be attributed to such effects and must be explained by other factors (see previous post on quantifiable causes related to urban hydrology and infrastructure hydraulics).
Unfortunately we live in an age where infographics rule. It is easy to make statements in the media that go unchecked. Infographics like those on the right and unsupported "Weather Story" claims are easy to find. A careful look at data is rare to find.
Unchecked facts were part of a recent case where the CBC Ombudsman had to admit that the CBC 'failed to comply with journalistic standards' in assessing and reporting on the insurance industry and other researcher claims that extreme rainfall has increased. The story was covered in the Financial Post by Terence Corcoran. The original story that was corrected to reflect journalistic standards is here: How to mitigate the effects of flood damage from climate change by Marc Montgomery.
As the CBC notes in the correction "Both this article and the subsequent “Counterpoint” have been modified as a result of complaints by Robert Muir (P Eng) to the Radio-Canada Ombudsman regarding inaccuracies in the stories . The ombudsman has ruled in favour of the complainant. Certain statements relating to rainfall amounts and the so-called 100 year events deemed by the complainant to be inaccurate or irrelevant to the story have been removed and/or replaced. Information from Environment Canada has been added to indicate their statistics show no increase in rainfall or extreme rain events beyond “normal” variations."
The Minister's letter would appear to support the fact that statistics show no increase in extreme rainfall events beyond normal variations. This is a good sign, and should help guide us toward effective, evidence based policies on managing floods
and flow. As I noted in the abstract of my paper Evidence Based Policy Gaps in Water Resources: Thinking Fast and Slow on Floods and Flow the fundamentals of rainfall extremes have often been overlooked and heuristic biases have skewed how we define risks:
"Water resources management and municipal engineering practices have matured in Canada over recent decades. Each year, more refined analytical tools are developed and used in urban flood management. We are now at a state where practitioners must use these tools within broad decision making frameworks to address system risks and the life cycle economics of prescribed solutions. Otherwise, evidence based policy gaps in the prioritization of risk factors and damages will widen and lead to misdirected mitigation efforts. For example, despite statistically significant decreases in regional short duration rainfall intensities in Southern Ontario, extensive resources are devoted to projecting IDF curves under climate change. Thinking fast, as defined by Daniel Kahneman, through listing recent extreme events to declare new weather reality risks based on heuristic availability biases, has replaced data driven policy and the statistical rigour of thinking slow problem solving. Under this skewed risk perspective, a high profile Ontario commuter train flood was mischaracterized as an unprecedented event despite a <5 y return period and a greater flood weeks before. Recent Ontario urban flood incidents have been attributed to unprecedented weather despite GIS analysis showing more critical hydrologic drivers. Constraints on effective water management are now less likely to be technical but rather scientific (inadequate representation of urban groundwater systems), institutional (arbitrary boundaries between city and watershed agency jurisdictions), economic (unaffordable green infrastructure solutions based on cost–benefit analysis and flat normalized loss trends), or operational. Evidence based policies and water management solutions are needed from a broad risk and economic framework that recognizes these barriers and uncertainties in the application of analytic tools.
Minister McKenna letter on observed extreme rainfall: