Showing posts with label wild weather. Show all posts
Showing posts with label wild weather. Show all posts

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 https://www.toronto.ca/wp-content/uploads/2018/04/982c-Torontos-Future-Weather-and-Climate-Drivers-Study-2012.pdf.  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.

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


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 https://www.cityfloodmap.com/2015/10/bogus-statements-on-storms-in-cbcnewsca.html

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: https://www.cbc.ca/news/canada/windsor/more-than-half-of-homeowners-insurance-claims-stem-from-water-damage-broker-says-1.3291111) 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: https://drive.google.com/open?id=1o9nUurzw_SkONJTbdEEp9OysNjCVtLxa
Link to the decision in French: https://cbc.radio-canada.ca/fr/ombudsman/revisions/2019-01-28

This was in response to a story by CBC's Marc Montgomery that has been corrected: https://www.rcinet.ca/en/2019/01/30/how-to-mitigate-the-effects-and-flood-damage-from-climate-change/
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: https://www.rcinet.ca/en/2019/01/30/response-to-a-climate-change-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"
https://www.cbc.ca/news/technology/canada-warming-at-twice-the-global-rate-leaked-report-finds-1.5079765 in April 2019. The article referenced Environment and Climate Change Canada’s (ECCC’s) Canada’s Changing Climate report https://changingclimate.ca/CCCR2019/ 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.


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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

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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.

Southern Ontario Observed Rainfall Intensities Decreasing - Annual Maximum Values Lower In Environment and Climate Change Canada's Engineering Climate Datasets (Version 3.0)

Ontario extreme rainfall annual maximum design intensity IDF trends climate change
Long term southern Ontario observed maximum rainfall trends,
according to Environment and Climate Change Canada's Version 3.0
Engineering Climate Datasets - decreasing trends in rain intensity and
more significant decreases than increases. 
Good news! Rainfall intensities have been decreasing in Ontario, Canada's most-populated province according to newly-released data. Less intense rain means lower urban flooding risk, contrary to many media reports that have confused future predictions of more extreme weather as a climate change effect with actual observed changes in the past. 

Maximum annual rainfall amounts over short durations at Ontario climate stations are used to derive engineering design intensities used in design of infrastructure such as sewers, culverts, channels, and ponds - the things that help convey rainfall runoff safety away from otherwise vulnerable people and property.

Environment and Climate Change Canada (ECCC) has recently updated its Engineering Climate Datasets that include a statistical analysis of observed trends in maximum values observed each year. The newest data are identified as Version 3.0 and are available as part of the Intensity-Duration-Frequency (IDF) Files on the ECCC website:
http://climate.weather.gc.ca/prods_servs/engineering_e.html

The previous Version 2.3 datasets showed decreasing annual maximum values at 21 southern Ontario climate stations with at least 30 years of observations - see previous post.

The updated Version 3.0 datasets continue this decreasing trend, showing that at the same 21 climate stations with an average observation period of 47 years:

  1. There are 42% more decreasing trends than increasing ones across all durations and stations (55.6% decreasing trends vs. 39.2% increasing ones).
  2. There are 75% more statistically significant decreases than increases (7 significant decreases vs. 4 significant increases).
This table shows the station name, ID, trends for each duration of 5 minutes to 24 hours, as well as the length of record and the most recent year in the Version 3.0 dataset.

Ontario Severe Rainfall Trends Climate Change Effects on Extreme Weather
Southern Ontario Observed Maximum Rainfall Trends - Environment and Climate Change Canada
Engineering Climate Datasets - Version 3.0
Trend Direction and Significance for 21 Climate Stations with Long Period Records (Greater than 30 Years)



Other observations:

  1. There are no statistically significant increases for durations less than 6 hours - that means the short duration convective storms burst that can lead to urban flooding related to most infrastructure systems do not show any appreciable increases.
  2. Overall downward trends are contrary to insurance industry statements, particularly the disproved "Telling the Weather Story" claim that there has been a one standard deviation increase in the probability of extreme rainfall according to Environment Canada data (the "Story" was only a theory/concept incorrectly cited and widely misreported as real data).
  3. Overall downward trends are contrary to many media reports citing a new normal of wild weather. Fortunately, some media, lead by the the Financial Post's Terence Corcoran are engaged in a critical review of urban flood drivers including extreme rainfall and the means to mitigate flood damages:
  4. CBC staff and the CBC Radio Canada Ombudsman have helped focus on facts Environment and Climate Change Canada data and corrected many stories on increasing storm frequency or intensity as noted here:
  5. Analysis by the School of Engineering at the University of Guelph, published in the International Journal of Environmental Research in 2015, looked at monthly trends and suggested that "The decrease in August extremes seems to have a significant impact on the annual extremes in the southwest and southeast regions": https://drive.google.com/file/d/1AngUYFFlm-RqQlmSC0gZqxy8nV61BW8J/view

Urban flooding is certainly an important issue to be addressed. And there are many factors that affect today's flood risks as explored in a previous post. While the insurance industry has suggested a link between increasing flood damages to increasing rain extremes due to climate change, given the wealth of evidence pointing to other quantifiable factors like increasing hydrologic and hydraulic stresses - and no change in rainfall extremes! - means that there is not even a correlation much less a causation relationship between flood damage and rain extreme trends (i.e., damages are up but rain intensities are down). This was pointed out in my Financial Post OpEd

Effective flood mitigation strategies must recognize the intrinsic capacity limitations in the vast amount of legacy infrastructure built over 30 years ago, and focus on reducing risks by addressing any level of service gaps through adaptation. Cost-effective and timely methods can include increasing the conveyance capacity of grey infrastructure, as opposed to mitigating rain/weather stresses that have not appeared to change, based on official, national engineering datasets. While such infrastructure investments should consider potential future climate effects, and we have many examples of analyzing stormwater and wastewater systems for such effects, past trends do not point to an increase to date in rainfall extremes. As a result, derived intensity duration frequency values for the stations reviewed above, based on values in the Version 3.0 datasets, shows an overall decrease in design intensities for small frequent and large rare storms across southern Ontario - those results were presented in a previous post, as shown below:

Ontario extreme rain IDF trends
Ontario Intensity Duration Frequency (IDF) Trends - 2 Year to 100 Year for all Durations
Environment and Climate Change Canada Engineering Climate Datasets - Version 3.0

Recognizing trends in observed rainfall maximum values and the derived design intensities will support data-driven, evidence-based policies and programs for achieving flood resilience through strategic infrastructure investments.

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The following table explores annual maximum values at Ontario climate stations with over 50 years of record:
Ontario Extreme Rainfall Severe Weather Storm Trends
Ontario Observed Maximum Rainfall Trends - Environment and Climate Change Canada
Engineering Climate Datasets - Version 3.0
Trend Direction and Significance for 11 Climate Stations with Long Period Records (Greater than 50 Years)

The table expands into higher latitude eastern Ontario communities including Kingston and Ottawa as well as to northern Ontario. The eastern Ontario climate stations show an overall consistent trend in decreasing observed rainfall maxima over the shortest durations. Another eastern Ontario station, the Ottawa Airport also shows decreasing trends over short durations, including several statistically significant decreases (i.e., lower observed rainfall intensities) for durations of 10 minutes, 15 minutes and 1 hour.

Previous analysis of the Version 2.3 datasets showed the differences in southern and northern Ontario trends. Increases in intensities in the north, beyond Ontario's largest urban centres, could reflect a shift toward more rainfall events instead of snowfall as a result of warming temperatures.