Green Infrastructure Cost - Ontario Tender Costs Support Economic Analysis for Master Plans, Asset Management, Retrofit Strategies

Numerous green infrastructure, low impact development (LID) stormwater best management practices (BMPs), projects have been implemented in Ontario and across North America. To support planning studies and strategy development, capital costs for implementation are required.  The following table summarizes recent project costs, based largely in Ontario.

The average cost per treated hectare is $530,000 (total project costs are weighted by total project area).  The design volume for the majority of the projects is not available.

Cost of Green Infrastructure Ontario
Ontario (and Alberta) Green Infrastructure Costs

The cost for these LID measures varies according to the type of feature as shown on the following chart that plots cost vs. service area (drainage catchment controlled).  Projects were grouped by type where possible, although some projects may incorporate more than one type in a treatment train.  The chart illustrates that Infiltration Trenches have the lowest cost per drainage area served. Rain Garden & Bioswales have the highest cost.

Green Infrastructure Cost Ontario
Ontario (and Alberta) Green Infrastructure Cost by Type of Low Impact Development Measure
Previous posts summarized costs from programs in the US.  The summary of 39 Ontario (and a couple Alberta) projects represent a total capital cost of $19.2M and a total service area of 36.2 hectares.  This area is comparable to the area of costed green infrastructure projects in the US EPA International BMP database.

The following table compares cost by LID type for three sources, the Philadelphia CSO control program, the ES UPA BMP database, and the compiled Ontario (and Alberta) tenders noted above.  The Philadelphia and the US EPA data both include design storage volume that may be considered for achieving different types of stormwater management goals (i.e., levels of service / performance outcomes).

Green Infrastructure Cost LID Cost
Green Infrastructure Costs by Type and Design Volume - Philadelphia CSO Control Program, US EPA BMP Database, and Ontario (and Alberta) Completed Projects

Some key observations are that porous/permeable pavement has a relatively high cost per drainage area ($/ha), however the cost per storage volume is relatively low for the US EPA datasets - this warrants further review.  The Ontario/Alberta porous/permeable pavement costs per area are also relatively high, compared to other types.  Just like Ontario/Alberta data, Philadelphia and US EA data shows lowest cost per hectare for infiltration/exfiltration projects.  The infiltration/exfiltration cost per storage volume was relatively low for both the US EPA and Philadelphia datasets.

The Philadelphia green infrastructure projects achieve a high volume, equivalent to 38.9 mm over the catchment area draining to it.  In contrast, the US EPA storage volumes are equivalent to only 6.6 mm.  The Philadelphia projects are sized for 1-2 inches of storage to achieve CSO control.  In contrast the US EPA projects are sized to achieve other benefits, such as watershed protection.

While the Philadelphia cost per area is highest at $857,000 per hectare, which is 4.1 times the US EPA database cost of only $208,000 per hectare, the unit cost per storage is in fact less.  The Philadelphia unit cost is $22,000 per hectare-mm.  The US EPA cost is $32,000 per hectare-mm, reflecting lower cost efficiency for smaller installations perhaps.

Using these unit costs one can estimate the budget required to retrofit green infrastructure into older urban areas to improve stormwater management.  In Ontario, the urban area built by 1966 has been estimated to be 110,000 hectares (Ducks Unlimited mapping), and by year 2000 to be 852,000 hectares (provincial SOLRIS land use mapping v2).  Assuming that 200,000 hectares require significant storage to achieve flood control in older communities, the retrofit cost would be $171 billion, applying the $857,000/hectare unit cost.  Or to provide improved water quality and water balance controls to the year 2000 urban area, the retrofit cost would be $177 billion, applying the $208,000/hectare unit cost.  Both of those costs represent considerable sums, given the Ontario stormwater infrastructure deficit of about $6.8 billion - that is the retrofit cost would be over 25 times that current deficit.  Given that, a strategic approach to retrofitting older communities is required, including prioritization of retrofit areas, implementing on higher-performance sites (e.g., permeable soils), implementing on highest risk tributaries (sensitive habitat, infrastructure or property risks), and considering the most cost effective measures, e.g., higher volume/centralized facilities that exhibit lower unit costs for storage, and feature types with lowest unit costs (i.e., infiltration/exfiltration facilities, and (to be confirmed) porous/permeable pavement).  The operation and maintenance costs associated with porous/permeable pavement should also be considered in the development of a retrofit strategy (i.e., consider full lifecycle costs including both capital and operating costs).


Update May 1, 2020

A few additional projects have been added to the cost table, including some updated costs for previously listed projects.  The added projects are the bottom six projects, representing an update for the Brampton County Court SNAP bioswale and the Newmarket Forest Glenn Drive LIDs.  The added projects are from the TRCA's cost review report to assess the updated LID lifecycle costing tool (LCCT Sensitivity Analysis A total of 47 projects are now included.

The weighted cost per hectare has increased slightly to $540,000 per hectare of drainage area.

Across Ontario, the areas that could be retrofitted with LID controls is extensive. The new provincial SOLRIS land use data has been reviewed to assess what the province-wide retrofit cost could be considering:

1) Urban impervious area = 344,000 hectares
2) Transportation area = 295,000 hectares
3) Urban pervious area = 93,000 hectares

Controlling runoff for all such areas with green infrastructure LIDs would cost $395,000,000,000 - that is, $395 billion assuming a unit cost of $540,000 per hectare.


The LID Cost Summary Table above presented costs per cubic metre so that the cost to achieve performance benefits through storage, e.g., water quality improvement, erosion stress reduction (water balance controls), or peak flow control, can be determined by those analyzing system performance. The costs in Philadelphia were $2,200 / cu.m for large volume controls (38.9 mm on average) while EPA BMP database costs were higher at $3,730 / cu.m for smaller controls (6.6 mm on average).

The added / revised Ontario projects include design volumes as well and so costs have been normalized by storage volume as shown below:

The Ontario cost per cubic metre is lower at $823.  This area-weighted cost reflect the very low unit cost of the Brampton bioretention rain garden of $297/cu.m - that cost is roughly an order of magnitude lower than the Philadelphia and US EPA BMP database costs for such features.  The median cost per cubic metre for these Ontario projects is $2,600, similar to the Philadelphia and US EPA cost.

Investing in Canada's Future: The Cost of Climate Adaptation - does infrastructure spending recommended in a new report for by IBC for FCM make sense?

Investing in Canada's Future: The Cost of Climate Adaptation
Investing in Canada's Future: The Cost of Climate Adaptation,
Report by IBC and FCM, September 2019 
A new report by the Insurance Bureau of Canada attempts to answer an important question: How much should we invest in adaptation measures to prevent effects of climate change?

The report summary "Investing in Canada's Future: The Cost of Climate Adaptation" (link) suggests the following:

"The analysis determined that an average annual investment in municipal infrastructure and local adaptation measures of $5.3 billion is needed to adapt to climate change. In national terms, this represents an annual expenditure of 0.26% of GDP."

"Flood, erosion and permafrost melt are associated with the highest cost to GDP ratios at 1.25, 0.12 and 0.37, respectively. These climate risks require the greatest investment in adaptation."

The infographic summary (link) suggests that " the benefits of investing in community adaptation and resilience outweigh the cost of such investments by a ratio of 6 to 1".

Let's review this in terms of mitigation of flood damages.

The annual expected insured losses from hydrologic and meteorologic events in Canada is $0.7B based on Munich Re data.  Overall losses are $1.27B considering Munich Re ratios.  Over 100 years that some infrastructure lasts, that is $127B in losses, some that can be effectively mitigated or deferred.  If there is a 6:1 benefit:cost ratio to adaptation efforts, then spending $127B/6 = $21.2B would be the cost of the adaptation program to 'break even' (let's assume that is the capital cost and not operation and maintenance).

The IBC FCM study suggests spending of $5.3B per year - a lot more than the 'break even' number -and notes "What is needed now is an ambitious and long-term investment plan for disaster mitigation and adaptation charted along a time frame of not year-to-year, but for the next twenty years or longer."

Let's look at the numbers.

If we invest $5.3B per year for 20 years, that is $106B. So that is a benefit:cost ratio of $127B:$106B or 1:2:1.  If we invest $5.3B a year for 25 years, the cost exceeds the benefits.  That investment is a lot higher than what we would expect if we achieved a 6:1 benefit:cost ratio, spending only $21.2B.

If we consider that losses cannot be completely deferred with adaptation (as it is rarely 100% effective, and there may always be events that exceed design capacity leaving residual damages, and overall losses cannot be completely deferred), the potential benefits over 100 years may be only $70B, assuming all insured losses can be mitigated.  That means spending $5.3B a year for 20 years, or $106B will cost more than the benefits.

This should be carefully reviewed.  The value of all municipal storm and wastewater and bridge infrastructure in Canada is $418 B (see my 2018 CWWA presentation here). So investing $106B, or 25% of the value of all that infrastructure value is a lot.  Some municipality flood mitigation programs has been estimated at only 6% of asset value.

Setting investment levels appropriately is important and further analysis is needed.  It would also be worthwhile distinguishing between the cost to address today's infrastructure capacity and land use planning risks and future risks.  Much of Canada's current $0.7B in damages is due to existing level of service deficiencies and not future climate effects.


In a previous study Green Analytics acknowledged the difference between damages due to economic growth and those due to future climate effects.  It would be worth looking at effects of future growth on damages and consider those in assessing infrastructure investment requirements.

Extreme Rainfall Trends in Canada - Engineering Climate Datasets for Long Term Climate Stations Show Increases and Decreases

Environment and Climate Change Canada's Engineering Climate Datasets includes trends in observed annual maximum rainfall over durations of 5 minutes to 24 hours.  Version 3.00 of the data was released in early 2019 (see Intensity-Duration-Frequency (IDF) Files and Google Drive link to trend charts grouped by province and territory  The following table shows trend direction and significance for stations across Canada.  It represents 3993 station-years of data, with an average of 47 years of data at 85 stations.
Some observations:

- out of 85 stations with trends over 9 durations, 7.9% of trends are statistically significant increases

- 1.8% of trends are statistically significant decreases

- the total of significant increases and decreases (7.9+1.8=9.7%) is mostly explained by chance (5% could be explained by random chance, due to the natural variability of the data)

- there are more increases than decreases with the exception of Ontario where southern Ontario has more decreases than increases, while northern Ontario has more decreases

- southern Ontario has 50% more significant decreases than increases

- Alberta is almost even with increases and decreases, and has no statistically significant increases, and just one significant decrease

- statistically significant increases are more prevalent for long durations over 1 hour (10%), than for short durations of 1 hour or less (6.4%) .. so significant increases for short durations are slightly above the % explained by randomness in the natural variability, in contrast, long durations have more significant increases than would be expected by chance

- statistically significant decreases are more prevalent for short durations of 1 hour or less (2.1%), than for long durations of over 1 hour (1.5%)

A review of these trends based on earlier v2.30 datasets, specifically stations with 20 years of record between 1965 and 2005, was presented by Shephard et. al in Atmosphere-Ocean in 2014:

"Summary statistics in Table 6 show that for all durations fewer than 5.6% and 3.4% of the total number of stations have significant increasing and decreasing trends in the AMS amounts, respectively. The highest percentage of stations with significant trends from any duration is 7.8%
(5.6% + 2.2%) for the 24-hour duration, which is close to the nominal 5% significance level. Based on this IDF single station analysis, and the more general single station climate results from the 1965–2005 period presented in Section 4a, we conclude that the annual maximum short duration rainfall values across Canada typically do not show a significant trend. Thus, for most of the single station IDF stations across Canada there is no evidence indicating that the stationarity assumption used in the traditional national EC IDF calculations has been violated. These results are not unexpected given the typical high variability and relatively short time series of the extreme short-duration rainfall observations."

Therefore Environment and Climate Change Canada find 'no evidence' that data used in IDF calculations is changing (values are stationary), and significant trends are generally no more than the natural variability would suggest.


The version 3.1 datasets have just been released.  An assessment of trends at all stations is included in a new post: - it also shows how trends have changed from older data sets (right chart) to the most recent sets (left chart) - no appreciable change.

Annual Maximum Rainfall Trends in Canada - Engineering Climate Datasets
Canadian Annual Maximum Rainfall Trends and Statistical Significance
The version 2.30 dataset was updated with data up to 2013 in 2014.  Version 3.00 was updated in early 2019 with some stations updated to 2017 but some with last update as far back as 2007.  The version 3.10 fills in many recent gaps and adds more stations - there were 565 in v2.30, 596 in v3.00 and now 651 stations in v3.00.  The v3.0 trends across Canada are shown below.
Annual Maximum Rainfall Trends in Canada - Environment Canada Engineering Climate Datasets v3.00 (released 2020) - trends per Environment Canada file idf_v3-10_2019_02_27_trends.txt

Assessing the Damage. CBC Ombudsman Finds Wrong Flood Damage Values Reported, Notes "broader concern that there is a pattern of imprecision in CBC’s coverage relating to flood events"

The CBC Ombudsman has found violations in the CBC’s Journalistic Standards and Practices related to an April 11, 2019 article entitled "Canada's building code is getting a climate change rewrite. Is your home ready?" (link).

The violations relate to publishing the wrong value for flood damages resulting from a Toronto August 2018 storm, and failing to note corrections to an article.

The CBC has always been very responsive to feedback on extreme weather reporting, including on the frequency of extreme events.  In January 2019, the Ombudsman also found violations related to reporting of more frequent extreme rainfall events (i.e., 100-year storms) - corrections to a couple stories were required.  Those Ombudsman's findings are noted in a previous post.  Other CBC story corrections have been made since 2015, again relating to storm frequency and the causes of flooding, and are noted in this previous post.

The new Ombudsman findings are described here.

While the complaint surrounding the April 11, 2019 article is related to a single storm, the Ombudsman noted that there is a broader issue stating:

"I have a broader concern that there is a pattern of imprecision in CBC’s coverage relating to flood events."

This comment is based on the fact that the cited average flooded basement claim or payout was $43,000 was really based on an extreme 2013 flood event in Toronto - not an average at all - yet it has been repeated over and over by the media including CBC.

A previous post shows how this value started (as $40,000 back in 2017) and how it has been expanded to cover the whole country.  It has been used in Intact Centre on Climate Adaptation's infographics as well:

Intact Financial Corporation's website refers to the $43,000 value too:

Global News. The Globe and Mail. Canadian Underwriter. TVO's The Agenda. All repeat the incorrect $43,000 value. Only CBC has been keen enough to entertain a review and make corrections to the record.

The full review is noted below for reference

Assessing the Damage
  • Sep 20, 2019
    CBC reported that concerns about climate change are causing government to re-think the rules for construction of buildings and infrastructure. Complainant Robert Muir took exception to several details in the online article. Among them was an estimate of damage caused by one particular storm, which led to this review about expert sources, and the importance of precision in journalism.


    You listed four deficiencies in the original version of a story headlined Canada's building code is getting a climate change rewrite. Is your home ready? which was published on April 11, 2019.
    The article concerned various proposals to create tougher standards for the construction of buildings and infrastructure projects in Canada. It explained to readers that governments are considering these changes in order to mitigate the expected impact of a changing climate.
    Two of your points prompted CBC News to make amendments to the article. One concerned wording that implied that predicted changes in extreme rainfall events had already been demonstrated. The other concerned the use of incorrect terminology to describe a backwater valve. Many homeowners will recognize this device which can decrease the risk of a sewage backup in their home.
    Your third point suggested the article should have more fully addressed the cost effectiveness of the various proposals.  In response, CBC News explained that this was outside of the scope of this particular article. 
    You were satisfied that those three points were properly addressed. However, on your fourth point, you requested a review. The remaining dispute relates to a section of the article which included an interview with Natalia Moudrak, Director of Climate Resilience at the University of Waterloo's Intact Centre. At one point she discussed the amount of damage caused to homes by flooding in Toronto.
    Here is the relevant excerpt of the article:
    While architects and construction workers grapple with reducing emissions from large buildings, average Canadians will face other problems. 
    "Flooding is the biggest challenge" linked to climate change for most homeowners, said Natalia Moudrak, director of climate resilience at the University of Waterloo's Intact Centre. 
    And there are measures homeowners can take now to safe address flooding.
    If a homeowner has a pump to get water out of a basement, "it's important to install a backup generator," she said. Widespread flooding often leads to power outages, leaving regular pumps useless when they're most needed.
    Homeowners can also take simple steps to elevate valuables, like expensive electronics, off their basement floor or put items in plastic or steel containers in case water does creep in, Moudrak said. 
    To prevent sewage from flowing into your home during a flood, David Foster, a spokesperson for the Canadian Home Builders' Association, recommends installing a backwater valve, a mechanical backflow prevention device linked to the plumbing and designed to allow water from sewer drains to only flow away from the home.
    "There is not a lot of cost involved in that, it just involves changing the way things are done," said Foster, who has consulted with the government on the new code. 
    When constructing a new home, installing a backwater valve costs roughly $400, Moudrak said. When retrofitting an existing home, it usually costs about $3,000. But municipalities often offer subsidies to help offset that expense.
    The problem, she said, is most people don't know about them.
    Only six per cent of Toronto homeowners took advantage of the city's flood resilience subsidy program, she said. When floods hit the city last year, she said the average cost to affected homeowners was $43,000.
    The sentence at the heart of your complaint is the very final one. You wrote that the $43,000 figure was “misstated”. It reflected the Intact Centre’s Toronto 2013 Flood Report, not the 2018 one (i.e. - the article states “last year”). You also suspected that the calculations of the estimate are based on studies done in the United States by the National Flood Insurance Program.
    You said more accurate numbers could be obtained from the CatIQ database, which you describe as “the definitive source for compiled flood damages from Canada’s insurance companies.” Based on the number of claims and total value of payouts from the 2018 storm, you suggested that a more accurate number was $18,509 rather than $43,000. You wrote:
    I believe that it is important to clarify given the fact that urban flooding is a significant issue, the costs of risk reduction are immense, and sound economic data and analysis is required to make evidence-based decisions on damage reduction management strategies. Flood damage data is a key piece of this economic data and many municipalities have cited the $43,000 value in federal infrastructure grant applications, which may not reflect actual damages, and could therefore adversely affect how scarce resources are allocated to address an important infrastructure challenge. 


    Paul Hambleton, the Director of Journalistic Standards and Practices, responded on behalf of CBC News:
    To be clear, the story quoted Natalia Moudrak, director of climate resilience at the University of Waterloo’s Intact Centre on Climate Adaptation: “When floods hit [Toronto] last year, she said the average cost to affected home owners was $43,000”. That information is also included in Weathering the Storm: Developing a Canadian Standard for Flood-Resilience in Existing Communities, a report published in January and co-authored by Ms. Moudrak.
    In a footnote, the report attributes that estimate to the Insurance Bureau of Canada (IBC) “based on Toronto flooding in 2013”. However, you wrote, the actual source is FEMA’s National Flood Insurance Program (NFIP) cited in a July, 2012 story in Forbes. The story cites the interactive “Cost of Flooding” found on the NFIP page as estimating nearly $40,000 damage to a 2,000 sq. ft. home after a 6-inch flood.   
    It’s interesting to note that in looking at it now, almost seven years later, “Cost of Flooding” estimates damage of a little over $20,000 for a 1,000 sq. ft. home and about $52,000 to a 2,500 sq. ft. one-storey home. (There was no estimate for 2,000 sq. ft. home).
    It’s pretty clear that there is a range of estimates and, it seems, little public information about how those numbers were reached. But you have touched on an interesting issue here.
    On one level, while reporters can tell us what they see and hear, there are many things that they don’t witness or can’t know. In those instances they attribute the information. That way, readers know the source and can make their own judgment about its reliability. In this instance, we attributed the information to Ms. Moudrak, identifying her position and the organization she works for.


    In a perfect world journalists would have expertise in every subject they cover. In the real world, many reporters, along with their editors, are generalists who strive to learn as much as they can in a short time so they can report faithfully and accurately on the subject at hand. 
    This means that there are times where they reasonably rely on subject experts to explain how something works, why something happens, or what might happen next. It might be a doctor, a realtor, or a marketing executive. In each case, the reporter looks to use their expertise as a way to improve the story with informed insights. 
    In such situations reporters willingly put themselves at the mercy of the expert’s knowledge. If an expert were to give bad information, CBC’s Journalistic Standards and Practices doesn’t let either of them off the hook. There is a section called “Responsibility and Accountability Related to Interviews” which reads as follows:
    CBC takes responsibility for the consequences of its decision to publish a person’s statements in the context it chooses. When we present a person’s statements in support of our reporting of facts, we ensure that the statements have been diligently checked. In the case of comments made by a person expressing an honest opinion, we ensure that the opinion is grounded in facts bearing on a matter of public interest.
    The interviewee also takes responsibility for his or her statement. As a general rule, we offer the interviewee no immunity or protection from the consequences of publication of the statements we gather.
    Sometimes the experts provide a recitation of facts, but not always. Often they are called on to analyze a situation or express an opinion related to their field. It is sensible that there is wide latitude in these cases for what constitutes reasonable comment. Realtors may disagree on which way the housing market is going. Marketers may clash over whether that new trend will fizzle. Doctors may have varying levels of enthusiasm for a prospective new drug.  
    The estimate of how much damage the average affected homeowner experienced during Toronto’s big summer storm of 2018 falls into this category of commentary and professional judgment. There is no single demonstrable number that has universal support, so the reporter went looking for someone to estimate the total.
    You disagreed with the Intact Centre’s methodology. Instead, you pointed to the CatIQ database, which is an excellent starting point. However, as you know, that database represents only the payouts insurance companies made to people who put in a claim. Others might think you should add in property damage not covered by the insurance policy, or people who opted not to file a claim. There are other expenses that could be considered as well. Should you include the value of time homeowners missed from work as a result? What about the cost of infrastructure repairs absorbed by government, or the cost of policing, firefighters and ambulance drivers? Should they be included or costed separately?
    Looked at through a different kind of prism, how much of the damage was caused by flooding, and how much was caused by wind, or by lightning? 
    Now, I recognize that you know a great deal about all these subjects. You have your own expertise, and you have told me about work you are doing that seeks to consider both direct and indirect costs to come up with a ratio of overall losses to insured losses. However, it is apparent that determining an estimate has at least some degree of subjectivity. 
    With all that in mind, it was acceptable journalistic practice for the CBC reporter to use the Intact Centre as its expert source and ask them to estimate the damage from a big storm. The Intact Centre is an applied research centre affiliated with the University of Waterloo. That may not bring it reputational immunity, but it does come with an inherent base level of credibility. The reporter was entitled to use Ms. Moudrak as an expert, so long as he attributed the estimate to her. I disagree with you that the JSP standard of “diligent checking” of her statement meant the reporter should have done extensive research to test that estimate. It is more reasonable to believe that diligent checking refers to facts that can be categorically confirmed or refuted, not to a matter of professional judgment such as this. 
    Nonetheless, you are correct that the number in the story WAS the wrong number, regardless of the quality of the estimate. The $43,000 figure did not represent the Intact Centre’s estimate for the 2018 Toronto storm, but instead was their estimate for the 2013 Toronto storm - something raised by you in your complaint, acknowledged by Mr. Hambleton in his response, and confirmed in my own communication with Ms. Moudrak.
    That this was wrong is, naturally, a violation of policy. That it has not been corrected means it continues to be so. It does not matter whether the original misunderstanding was caused by the source or by the journalist. It ought to be clarified for the record, and for the readers. 
    Further, I noted while reviewing the story that there is no note on the web page acknowledging the two other corrections prompted by your initial complaint. This is a second violation of policy.   
    I have a broader concern that there is a pattern of imprecision in CBC’s coverage relating to flood events. You provided me with a list of other recent CBC stories which make reference to the $43,000 damage estimate. Several confuse the matter by not indicating this is a specific estimate for the 2013 Toronto floods. One said, “The average basement flood in Ontario costs the homeowner $43,000.” Another said, “The average payout for a flooded basement is $43,000 and rising.”  These types of references take a single (and unusual) event in 2013 and treat it as if it is now a generic standard.
    Reporters and editors need to ensure they understand what's included (and what's not) in any estimates provided, and they need to ensure that they associate that estimate with the correct event - or events, as the case may be. Based on my review, that is not happening consistently enough. 
    All of this needs to be distinguished from your belief that the Intact Centre’s $43,000 estimate to be incorrect, even when attributed to the 2013 storm. I would encourage CBC News to take your perspective into account, but that is as far as I will go. It is not my intention to take sides on the quality of the Intact Centre’s estimate. If journalists continue to find the Intact Centre credible, they continue to be free to consult them for stories.
    Jack Nagler
    CBC Ombudsman

    Toronto Area Extreme Rainfall Trends - Comparing Engineering Climate Datasets with Future Weather & Climate Study Predicted Trends

    Environment and Climate Change Canada's Engineering Climate Datasets summarize observed annual maximum rainfall over various durations from 5 minutes to 24 hours.  Theses series are used to derive IDF tables and charts that describe the intensity, duration and frequency (i.e., return period) of extreme rainfall.  IDF tables are used to support engineering design of storm drainage and wastewater systems, and are used to define rainfall patterns used in hydrologic modelling.

    The City of Toronto commissioned Toronto's Future Weather & Climate Driver Study - the 2012 results indicate projected changes in extreme rainfall for a few durations and return periods.  Results of the Outcomes Report are here  The baseline period for the study is 2000-2009 and statistics are predicted out to 2040-2049.

    The Engineering Climate Datasets have been updated in early 2019, including for two Toronto-area climate stations with long records called "Toronto City" and "Toronto International Airport".  The following tables compares the predicted increase in extreme rainfall in the 2012 study with trends in the same statistics from 1990 to 2017 at these two Toronto-area stations.

    A key take away is that the Future Weather & Climate Driver Study does not agree with the direction and magnitude of changes in the actual statistics, which are based on real observations (not modelling predictions).  Some actual statistics have been decreasing since 1990, not increasing as predicted int eh study.  When a statistic is increasing, it is at a significantly lower rate that what is predicted in the study.

    The following chart compares the past 100 year daily data to the study predictions - the Toronto study seems to have a hockey stick shape, jumping significantly upward by the 2040's which does not match the past trends.

    The next chart shows changes in 10 year hourly rainfall. The Toronto study significantly understates the value today, suggesting it will double by the 2040's - the predicted future value has already been in place since the 1990's however.

    It is questionable whether the City of Toronto should consider any changes to design criteria for municipal infrastructure considering these future predictions - best to follow ASCE's approach and incorporate flexibility in future design and wait and see with the 'observational method'? - if observations show that there is no change in the statistics, there should be no significant driver in changing design criteria, especially based on models that do not match the magnitude or trend in actual extreme rainfall statistics.


    Bonus: here are a few more predicted 24 Hour 100 Year rainfall values, also going against the observed trends:

    John Robson of Climate Discussion Nexus Share Causes of Urban Flooding - Highlights CBC Ombudsman Findings on 100-Year Storms

    This blog has examined causes of urban flooding and non-causes of flooding too. A new video by the Climate Discussion Nexus examines causes of urban flooding and references the recent CBC Ombudsman review of 100-year storm trends (i.e., no changes in extreme rainfall).

    The video notes that we have always had flooding which is correct - that is something we have noted as well, like in this presentation to the WEAO / OWWA joint climate change committee:

    The presentation noted how GO Train flooding, Toronto Island flooding and Toronto basement flooding area note new phenomena as shown in these images:

    A review of the inquiry for Premier Davis on Toronto Don River flooding noted flooding since the 1800's as noted in this post: - an Environmental Assessment in 1983 noted this:

    This Acres Consulting report noted the influence of hydrologic changes on peak flows and flood damages. We have described these changes as well such as in this JWMM paper:

    GTA watershed urbanization changes were summarized as follows:

    Here is a wider perspective:
    And here are urbanization trends in other southern Ontario municipalities:

    We have assessed the trends in extreme rainfall which supported the CBC Ombudsman decision - here are the english-version findings:

    Even Minister McKenna has reinforced comments made in Canada's Changing Climate Report stating in a June 2019 letter "the observational record has not yet shown evidence of consistent changes in short-duration precipitation extremes across the country":

    Other CBC story corrections about extreme rainfall are summarized here:

    As the Climate Discussion Nexus video notes, the insurance industry has claimed that there is an increase in extreme rainfall caused by climate change - this has been reiterated by senior executives as in this op-ed in the Globe and Mail by Charles Brindamour and Dean Connor "Climate resilience must be part of every government’s agenda" (The Globe and Mail. September 25, 2018., or as in this op-ed in the Financial Post by Craig Stewart "Counterpoint: Insurance claim costs are rising because severe weather is making flooding worse" (Financial Post. February 7, 2019.

    Unfortunately, the insurance industry has not ever offered any data on increasing extreme weather trends to counter Minister McKenna's recent statement or the CBC Ombudsman findings since 2015. The insurance industry has in the past mixed up future predicted extreme rain trends with past observations as in the "Telling the Weather Story" report:

    As noted in our Financial Post op-ed, the insurance industry has claimed a correlation and causation between extreme weather and flood damages. Unfortunately, there is no rain trend to correlate to making any causation discussion moot. As Dr. Dickinson explains in the video, warmer winters mean lower spring flood potential, and urbanization drives urban flood stresses, not changes in rainfall. More on this University of Guelph analysis is here:

    Our rebuttal to the insurance industry's suggested correlation / causation was in the Financial Post:

    Well done John Robson and Climate Discussion Nexus for sharing information on this topic.


    More reading? - what do engineering studies in southern Ontario say about extreme rainfall trends? typically no past change - see compiled reports / analysis here:

    The Ombudsman has also recently noted in a new review that "It would have been wrong to state categorically that Canada has already seen an increase in extreme rainfall events" and that its reporting should be unambiguous about the past, present and future, with "distinctions made between observed phenomena and predicted phenomena" (  The Ombudsman notes that CBC reporting describes future changes in extreme weather saying:
    • 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.

    Are More 100 Year Storm Happening? Yes and No. A Proliferation of Rain Gauges Can Now Record More 100 Year Storms, But Fixed Locations Show No Increase

    There are many sensational media stories about ghost storms and ninja storms hitting urban areas, and a steady claim that we are experiencing more extreme rainfall, that is, higher intensities for a given probability (called return period), or greater frequency of given design intensities. Often it is stated that we are experiencing more 100 year storms today and that is a "new normal" brought on by a changing climate.

    How does the number of climate stations, or rain gauges, that are in operation affect the number of observed extreme events. Well, let's look at Toronto for example.  Several past extreme events were reported in the Staff Report on Impact of July 8, 2013 storm on the City's Sewer and Stormwater Systems dated September 6, 2016: (

    During the May 12, 2000 extreme rainfall event, Toronto operated 16 rain gauges as shown on the staff report map below.

    Fifteen years later, during the August 19, 2005 storm, the City operated 31 rain gauges as shown below, so almost double the number of rain gauges.  Look at the higher density of gauges in north Toronto where many higher August 19, 2005 rainfall depths were observed.

    Then 8 years later, during the July 8, 2013 storm the city operated even more rain gauges, i.e., 35 in total.

    And then a few years later, on August 7, 2018, the city operated 43 rain gauges - even more than 2013. I don't have a map but here is a super-cool graph summarizing Toronto Open Data rainfall totals at those gauges over a period of 5 minutes to 24 hours.

    And now today as of July 17, 2019, Toronto has 45 active rain gauges as shown in the following map presented to the Ministry of Environment Conservation and Parks' stormwater stakeholder group participating in development of minimum standards for ECA pre-approval.

    So let us summarize the trend in the number of rain gauges in the chart below.

    Astute blog readers will notice that the number of rain gauges has increased almost 300% since the year 2000. Yes, almost three times the number of rain gauges now. Obviously, more extreme events can be observed and recorded when the number of rain gauges increases dramatically.

    The following table shows that in the year 2000, there was a rain gauge every 39.4 square kilometres (16 gauges per 630.2 square kilometres). By 2019, there is a gauge ever 14 square kilometres.


    So what is happening at fixed locations where rain intensities are measured? In Toronto and Mississauga, many trends are downward according to the Engineering Climate Datasets:


    As a result, design intensities for short durations have been decreasing since 1990:


    To recap, many more rain gauges today mean we 'see' more storms - these are typically needed to support basement flooding Municipal Class EA studies (rainfall needed to calibrate hydrologic and hydraulic simulation models), to guide operational activities too.  Many municipalities have installed rain gauges to support inflow and infiltration management programs.

    We have a "finer mesh net" to catch these events and add them to our records - we have almost 3 times more rain gauges in Toronto since 2000.

    But no. Storm are not becoming more intense. If we see more of them, it is because we are looking harder for them with more extensive monitoring efforts. Given this expanding intensive network of rain gauges today, it is not uncommon, statistically speaking, to observe many 100-year storms over a short time period.  This earlier post explores those statistics in the GTA -

    CBC correcting claims on extreme weather trends since 2015 - more should follow their lead and more consistency is needed in CBC reporting

    See the latest at the end of this post (Jan. 2021). The CBC has done a great job in correcting its reporting of extreme weather frequency claims over the years. Other media organizations like TVO and major newspapers have been given the same feedback on inaccurate reporting as CBC but have not moved to correct exaggerated claims. But while CBC has made may corrections, both voluntarily by its journalists and through the coaxing of its Radio-Canada Ombudsman, it has a tendency to repeat past inaccuracies without benefiting from what it has learned - so there is an opportunity to have the CBC be more consistent in its reporting, even adhering better to its own standards.

    What are some examples of CBC's past corrections on extreme weather trends? Here are those that I helped move along.

    1) November 2015

    The CBC has corrected articles on this topic in the past as well dating back to 2015, confirming that there have been no changes in extreme rainfall. This correction was in response to a statement made by the insurance industry when an insurance broker stated we are having 20 times more storms today. This blog post describes the statement ""A lot of it has to do with the frequency of the storms and I think you could even extrapolate that it's got to do with climate change," ... "we're getting 20 times more storms now than we were 20 years ago." Here is a write-up on that exchange

    CBC issued a correction and wrote me a letter dated Nov. 20 2015 (see excerpt in blog post link above and at right) saying "Environment Canada verified that there has been no significant change in rainfall events over several decades". In the article (link: the correction is as follows:

    "However, Environment Canada says it has recently looked at the trends in heavy rainfall events and there were "no significant changes" in the Windsor region between 1953 and 2012."

    – this finding from 2015 is still valid today - a review of the updated Engineering Climate Datasets v3.0 released in March 2019 shows that across all of southern Ontario in fact observed rainfall intensities have been decreasing as engineering design “IDF” values have been decreasing as a result – this is shown for small frequency storms and large rare storms as well (see previous post on IDF trends, see previous post on decreasing annual maximum rainfall trends, see Stantec's review of Windsor Airport extreme rain trends in the December 2018 Windsor/Essex Region noted in this blog post and in the excerpt to the right - see "Conclusion: Short-term durations events are slightly trending downwards thus no evidence to increasing IDF curves for stormwater design").

    2) January 2019

    The recent CBC Ombudsman ruling [January 28, 2019] disputes statements made by Dr. Blair Feltmate of the Intact Centre on Climate Adaptation on the frequency of storms linked to flooding (100 Year storms).

    See link to decision in English:
    Link to the decision in French:

    This was in response to a story by CBC's Marc Montgomery that has been corrected:
    And corrections to a counterpoint story where I was interviewed by Marc Montgomery and where I had brought up concerns with the accuracy of the initial story:

    CBC originally stated “We are experiencing storms of greater magnitude, more volume of rain coming down over short periods of time these days due to climate change. That is causing massive flooding.” However  the CBC Ombudsman concludes that:

    "One only had to examine the official Environment Canada data for Ontario as well as for the entire country to acknowledge that the claim made in the article was inaccurate. Such acknowledgement would at the same time have addressed the complainant’s criticism regarding the lack of data to corroborate Dr. Feltmate’s claim about the increased frequency of extreme rainfall events in Canada."

    The Ombudsman also found that the CBC did not meet its own standards for accuracy and impartiality stating:

    "Review by the Office of the Ombudsman, French Services, CBC/Radio-Canada of two complaints asserting that the articles by journalist Marc Montgomery entitled How to mitigate the effects of flood damage from climate change and Response to a climate change story, posted on September 19 and November 19, 2018, respectively by Radio Canada international (RCI), failed to comply with the CBC/Radio-Canada Journalistic Standards and Practices regarding accuracy and impartiality."

    3) April 2019

    The CBC corrected this article entitled "Canada warming at twice the global rate, leaked report finds" in April 2019. The article referenced Environment and Climate Change Canada’s (ECCC’s) Canada’s Changing Climate report that reviewed extreme precipitation trends in Canada and stated:

    "There do not appear to be detectable trends in short-duration extreme rainfall in Canada ..." and "For Canada as a whole, there is a lack of observational evidence of changes in daily and short-duration extreme precipitation.

    The original article linked current flooding to changes in rainfall stating "Although flooding is often the result of many factors, more intense rainfall will increase urban flood risks."

    I highlighted sections of the ECCC report stating lack of evidence of changes in rainfall extremes and as a result, this is the correction CBC made in response:

    "Corrections, An earlier version of this story said that more intense rainfall contributes to increased urban flooding. In fact, while the report states that precipitation is higher overall, it did not find that episodes of short-duration extreme rainfall have increased or establish a connection between these and increased or exacerbated flooding. Apr 04, 2019 2:23 PM ET"

    4) May 2019

    In a April 11, 2019 CBC News article by Chris Arsenault entitled "“Canada's building code is getting a climate change rewrite. Is your home ready?” made the statement in the sub-headline “Increased flooding, wildfires and storms mean tough new rules take effect in 2025” which mischaracterizes trends in storms and flooding.

    I shared the Ombudsman findings from January 2019, and CBC's earlier corrections on extreme rain trends. I also shared information on key causes of flooding, highlighting urbanization as a key factor per IPCC reporting, ECCC's Canada's changing climate report, local university studies and Ontario case law.

    In response to this feedback CBC corrected the April 11, 2019 CBC News article per Paul Hambleton’s email to me on May 16, 2019. In response to the actual data showing no historical trends in extreme rainfall, CBC revised the sub-headline from “Increased flooding, wildfires and storms mean tough new rules take effect in 2025” to “Predicted increase in flooding, wildfires and storms means tough new rules take effect in 2025”.

    This is now accurate - there have been no changes to date but there are predicted changes in the future. Canada's Minister of Environment and Climate Change Catherine McKenna has confirmed the lack of observed changes in extreme precipitation in a June 13, 2019 letter to me (see right).

    In the letter she reiterates a statement made in Canada's Changing Climate Report stating: "the observational record has not yet shown evidence of consistent changes in short-duration precipitation extremes across the country" - The original report stated more simply (page 117):

    "For Canada as a whole, observational evidence of changes in extreme precipitation amounts, accumulated over periods of a day or less, is lacking."

    So bravo for CBC for making corrections to its reporting on extreme weather trends! No other media outlet has been receptive to making corrections based on feedback.  CBC's original corrections in 2015 are supported by new local and region data, and the recent corrections are supported by  Minister McKenna's recent statement and Environment and Climate Change Canada reporting. 

    4) September 2019

    The CBC Ombudsman Jack Nagler has reviewed the April 11, 2019 CBC News article regarding reported flood damages.  The Ombudsman's review is here entitled "Assessing the Damage".  It found that while there is uncertainty in how flood damages are estimated, considering direct and indirect costs (we agree), the article cited flood event costs that were plain "wrong" - the costs for a Toronto August 2018 flood event, supplied by the Intact Centre on Climate Adaptation, did not represent that event at all and related somehow to the July 8, 2013 event. The review reads:

    "The $43,000 figure did not represent the Intact Centre’s estimate for the 2018 Toronto storm, but instead was their estimate for the 2013 Toronto storm"

    The Ombudsman found a couple violations of CBC practices:

    i) The wrong damage value for the August 2018 Toronto storm/flood
    ii) Failing to document earlier corrections to the story (see point 3 above on those)

    A key take away is this (my bold):

    "I have a broader concern that there is a pattern of imprecision in CBC’s coverage relating to flood events. You provided me with a list of other recent CBC stories which make reference to the $43,000 damage estimate. Several confuse the matter by not indicating this is a specific estimate for the 2013 Toronto floods. One said, “The average basement flood in Ontario costs the homeowner $43,000.” Another said, “The average payout for a flooded basement is $43,000 and rising.”  These types of references take a single (and unusual) event in 2013 and treat it as if it is now a generic standard.

    Reporters and editors need to ensure they understand what's included (and what's not) in any estimates provided, and they need to ensure that they associate that estimate with the correct event - or events, as the case may be. Based on my review, that is not happening consistently enough."

    Me too on that broader concern.


    Recent CBC coverage seems to go back and repeat the same inaccurate statements that have been made in the past and that have been corrected. Especially for extreme weather trends and their effect to flooding. Perhaps CBC needs to promote what it has already found on the topic of extreme weather trends and that could help it carry forward with more accurate reporting in the future?

    Perhaps Ombudsman Jack Nagler's observation on the "pattern of imprecision", resulting in treating unusual events as standards (averages), will help improve CBC reporting related to flood events.

    R. Muir


    5) January 2021

    NEW! : see Radio Canada's harsh new review of June 2020 reporting on extreme rainfall trends: 

    Similar to the review in January 2019 described above, the Ombudsman has found additional violations of the broadcaster's JSP on the same topic by the same journalist - this has now resulted in Radio Canada management deleting the story that mistakenly 'confirmed' that extreme rainfall is more severe.