Urban Heat Island - A Local Climate Cause for Urban Flooding?

Urban flooding is often caused by high intensity rainfall, typical
during summer thunderstorms.

The Framework Convention on Climate Change points to climate change impacts on extreme weather events:

Article 8
1. Parties recognize the importance of averting, minimizing and addressing loss and damage associated with the adverse effects of climate change, including extreme weather events and slow onset events, and the role of sustainable development in reducing the risk of loss and damage.

As we move ahead, its important to quantify trends in extreme rainfall events, particularly as these relate to urban flooding. Recently Northern Illinois University (NIU) explored the effects of local urban heat island on storms.  We review this in the context of trends in Toronto-area extreme rainfall, as well as trends across Ontario and Canada.

NIU research suggests that local heat island effects increase the incidence of thunderstorms.  They found that for any given day in the 17-year study period (1997-2013) there was about a 5 percent greater chance that Atlanta would experience a thunderstorm compared to a similar sized rural area. As convective summer thunderstorms are the typical cause of urban flood damages, this could be one factor resulting in increased flood damages over past decades.

Researches studying Atlanta indicated that the possible mechanisms causing more thunderstorms in urban areas included:

• The urban heat-island effect. A landscape of concrete, asphalt and densely packed buildings can enhance heat. Low pressure forms atop the urban area with higher pressure in surrounding rural areas. The scenario might cause low-level atmospheric convergence, which forces air up into thunderstorms.
• Localized areas of upward moving air resulting from increased surface roughness. A cityscape modifies wind direction and speed, which might lead to enhanced convergence and thunderstorm formation.
• Urban pollution. The science isn’t settled on this issue, but some researchers believe enhanced aerosol production caused by urban pollution can enrich thunderstorms. “We discovered that there may be an aerosol effect with initiation as well, because we had greater storm initiation events during weekdays compared to weekend days.”

(So one possible solution to urban flooding is mandatory 3-day weekends all summer.  Sign me up!)

The Toronto area has been expanding since Governor John Graves Simcoe established the town of York in 1793. 

For comparison, Metropolitan Atlanta had a population of about 5.5 million in 2013 while the Greater Toronto Area population in 2011 was about 6 million.

Is it possible that the urban heat island effects from expanding Mississauga, Brampton, and Vaughan area have increased the incidence of storms over Toronto?

Bloor Street gauge shows no increase in severity of rainfall events
since the 1940's in downtown Toronto (Environment Canada).
Station 6158355.

Environment Canada Engineering Climate Datasets show no increasing trends in the severity of storms downtown at the "Bloor Street" gauge as we call it in the business. This "Toronto City" gauge trend data is shown to the right.

Often the characteristics of severity and frequency are used together. It is reasonable to expect that these move in the same direction when it comes to rainfall events.  That is, if there are ever more frequent events, then there is a higher probability that a more severe event can occur.  The Atlanta research looked into the frequency of thunderstorm 'births' but did not explore the resulting severity of the events.

Toronto Island Airport annual maxima for rainfall over
5 minute to 24 hour durations.  Station 6158665.

Given that the severity of rainfall events has decreased at the Toronto Bloor Street gauge, we could assume that the frequency of events has decreased as well.

Below the Bloor Street data is the Toronto Island Airport and the Buttonville Airport rainfall trends. Both of these locations show decreasing trends in the maximum rainfall depth measured over 5 minute to 24 hour periods each year. Is it possible that the relative stability of the land use around the Island and Bloor Street has meant stable thunderstorm patterns?

'Toronto' Buttonville Airport annual maxima for rainfall
over 5 minute to 24 hour durations.  Station 615HMAK.

Toronto International Airport (Pearson) annual maxima for
rainfall over 5 minute to 24 hour durations.  Station 6158731.

At the Pearson Airport gauge there is a mix in the trends in the maximum rainfall depths. The trend is downward for 5 minute durations and 6, 12 and 24 hour durations, but upward for 10 minute to 2 hour durations.  This data set is extended to include the large storm on July 8, 2013.

Is is possible that the development sprawing to the north and west of Pearson Airport contrbutes to an increase in the severity of annual maximum rainfall depths at Pearson for some durations? Lot likely.

Bear in mind the upward trends some some durations are Peason are minor and that even in a statistically static environment (no change in rainfall severity), trends naturally go up or down as more samples are taken from the underlying 'population' over time - it is just like variable results from a coin toss.  You statistically have a 50% chance of getting heads in the long, long run, but you also have a 6% chance of getting 4 heads in a row on your first tosses.

As we move past 2013 and clock smaller sub-record breaking events, the Pearson Airport trends may also follow the decreasing downtown and uptown Buttonville ones.

The one gauge that has been cited as having experienced many more extreme events over time is the North York gauge.  This is actually a composite data record gauge and so it should probably not be given as much weight as Bloor Street or Pearson which have longer records from more consistent locations.

'Toronto North York annual maxima for rainfall over 5 minute to
24 hour durations.  Station 615S001 (composite gauge).

The verdict? Are storms becoming more severe in the Toronto area and could this be caused by urban heat island effects? The answer is storms are not becoming more severe, and we also conclude no more frequent. This means that neither the macro scale effects of global climate change, nor the local scale effects of heat islands, nor the combination of the two, are having a measurable impact on rainfall patterns in Toronto.

What has certainly changed in the Toronto area to explain increased flooding? Urbanization has increased runoff and that land use change doubles or triples peak flows relative to rural conditions.  The Don River watershed urbanization has increased from 15% in the 1950's to nearly 90% today.  Also, overland flow paths have been enclosed or obstructed due to intensification and infill. Perhaps Ontario needs a "Places to Flow Act" to address deficiencies in the overland flood conveyance capacity in developing cities.

Days with rain include days with a fraction of a millimetre
of rainfall accumulation (anything above a trace amount).
Numbers are up but do not affect flood risks.

Several insurance companies have cited annual precipitation, or number of rainfall events per year as a factor in increasing flood damages, but this is really nonsense.  Understandably, urban flooding is a complex issue and annual precipitation would be a convenient explanation for it.  It is short term rainfall intensities as shown the in Environment Canada charts above that define urban flood risks.  "Days with rain" is  risk factor for mushroom growth on your front lawn.  We explore that in another post.

Looking beyond Toronto and its urban heat island context, Environment Canada's assessment of rainfall trends can be found in the report at the following link:

https://www.dropbox.com/s/pxbuyz7sx3h7ln0/Final%20December%202011%20Draft%20Regional%20IDF%20Technical%20Report.pdf?dl=0

This report is "Methodologies to Improve Rainfall Intensity-Duration-Frequency (IDF) Estimates: A Southern Ontario Pilot Study" by Environment Canada Adaptation and Impacts Research Climate Research Division, December 2011.  See Section
6.1 entitled Trends in Precipitation and its Extremes in Southern Ontario, page 77 for the following:

“Significant increases, as well as decreases, were detected at some stations in a number of the extreme precipitation indicators. However, the majority of station trends were determined to be non-significant and no consistent geographical patterns for increases or decreases were observed across Canada. In most cases, the magnitude of the observed changes was also very small. These results are consistent with the daily Canadian extreme precipitation trend analysis of Zhang et al. (2001) and the Canadian component of global and North American trend analyses of daily precipitation extremes by Alexander et al. (2006) and Peterson et al. (2008), respectively.”

As further information we can refer to the work of Heather Auld, M.Sc. (Meteorology) who joined Risk Sciences International (RSI) as their Principal Climate Scientist in 2011 after spending 32 years with Environment Canada. Please see her presentation on extreme rainfall trends here:

http://projects.upei.ca/climate/files/2012/07/IDFtraining-Auld-final.pdf

Ontario decreases and increases in short term rainfall intensities.

Slide 39 includes a map showing decrease in rainfall intensity (15 minute and 12 hour periods). Slide 40 summarizes overall trends and indicates:

"• Return Period Rainfalls DECREASE in many cases
• High profile extreme rainfall events in recent years lead to
 expectations that return period rainfalls will all show INCREASES"

Raw rain intensity and statistics data is available from Environment Canada here under the IDF files link:

http://climate.weather.gc.ca/prods_servs/engineering_e.html

Infographics Replace Rational Thought on Urban Flood Causes and Insurance Risks

I had a favourite Matt Groening cartoon on my grad school cubicle cork board for years.  It was a Life is Hell black and white strip from Now Magazine.  In it Binky is lying in bed awake all night and Mrs. Binky asks him "What is keeping you up?" and Binky replies "Infotainment".

Just as Binky worried about Infotainment then, I lie awake worried about Infographics now. Infographics per Wikipedia are:

"...graphic visual representations of information, data or knowledge intended to present information quickly and clearly. They can improve cognition by utilizing graphics to enhance the human visual system’s ability to see patterns and trends."

RSA links flood damages to more days with rain since the 1950's.
Ummm ... how about urbanization? The Don River watershed was
only 15% urbanized in 1950 and was 80% urbanized by 1994. In 2021
it is predicted to be 91% urbanized. Ahem .. any chance this is
contributing to flood damages? Changing development patterns instead
of changing weather patterns?

Given how busy we are, infographics are wonderful - they can get us up to speed on complex issues in no time flat apparently, distilling a whole bunch of science, statistics and mumbo jumbo into a quick, easily digested glance-friendly format.

Here is the Climate Smart Infographic from RSA Insurance related to their new Waterproof Coverage insurance endorsement.  Hmmm "Protect Property in Extreme Weather", got it. "Weather Changing", sure. "20 more days of rain than in the 1950's", logical explanation for flooding .. uh....wait .. WAIT A MINUTE!  I was almost "Infografected".

What is an Infographection? Its like an infection, easily transitted through exposure to infographics. It affects the weak minded mostly, turning them into a zombie-like herd of followers.  Be afraid be very afraid, because for some reason infographection is becoming the preferred method of communication for insurance companies and provincial agencies.

What is wrong with RSA's infographic? Well, "days with rain" has no bearing on extreme weather or causes of the flooding RSA is selling endorsements for.  If days with rain was relevant, then Vancouver would flood all the time and nobody would get insurance there.  What is forgotten in the RSA "days with rain" statistic is the fact that a tiny amount of rainfall can trigger the counting of a rain day.  How little rain?  Fractions of a millimetre of rain - hardly the events that cause urban flooding.

Inoculate yourself against infographection - this paper explores some the of details we can consider when thinking about number of days with rain by first considering the tiny 'trace' amounts that are recorded:

https://www.researchgate.net/publication/242397703_Adjustments_for_trace_measurements_in_Canada

As noted in the paper, operational changes have increased recording of rainfall events over time (not necessarily a fundamental increase in rainfall):

"The measurement of trace precipitation in Canada went through several phases over time. Not just the definition of trace precipitation (or the lack of definition) has been modified, but the measuring unit was also changed from imperial to metric system. All data in the Climate National Archive was converted from inches to millimetres with the introduction of metric system, which also caused further inconsistency in the data. Station relocations were often accompanied by new set of instruments and a new observer. The training given to the observers often resulted in a jump in the number of daily trace measurement."

Also, the switch to metric since the 1950's meant a smaller measurement unit, and meant its is now easier to record trace amounts and record a 'greater than trace' amount, i.e., a lawn mushroom-forming but not-flood-inducing "day with rain":

"The homogeneity of trace observation record was also seriously affected by switching from Imperial to the Metric system around 1977 - 1978. The units were given in inches before; the minimum measurable level has been decreased by almost 0.1 mm in the metric system. Table 1 gives a summary of the amounts and units used in both systems for rain and snow separately."

Threshold for measuring and recording rain events decreased in the 1970's with conversion to metric system.

So the RSA infographic and simple "days with rain" statistic really fails to explain any cause of flooding or trend in extreme rain characteristics.  As reader of this blog know, Environment Canada Engineering Climate Datasets show no increase in extreme rain characteristics that cause urban flooding:

http://www.cityfloodmap.com/2015/07/storm-intensity-not-increasing-old.html

The unfortunate situation for RSA and flood risks in their portfolio is that by Blaming it on the Rain like Milli Vanilli would, RSA ignores real factors that have caused flows in increase (with no increase in rain intensity), and that have caused infrastructure flow capacity to decrease. Here are some ideas on causes of flooding and flood damage increases:

http://www.cityfloodmap.com/2015/11/why-flood-damages-are-increasing-in.html

It seems RSA has been "infographected" by their own infographics.

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If you got this far, you might also like this article in Psychology Today "Anti-intellectualism Is Killing America, Social dysfunction can be traced to the abandonment of reason".  It highlights "What Americans rarely acknowledge is that many of their social problems are rooted in the rejection of critical thinking or, conversely, the glorification of the emotional and irrational.".  Is this just Daniel Kahneman's lazy-brain System 1 thinking at work?

Thinking Fast and Slow About Extreme Weather and Climate Change

Thinking, Fast and Slow is a best-selling^[1] 2011 book by Nobel Memorial Prize in Economics winner Daniel Kahneman which summarizes research that he conducted over decades, often in collaboration with Amos Tversky.^[2][3] It covers all three phases of his career: his early days working on cognitive biases, his work on prospect theory, and his later work on happiness.

The book's central thesis is a dichotomy between two modes of thought: "System 1" is fast, instinctive and emotional; "System 2" is slower, more deliberative, and more logical.

The book delineates cognitive biases associated with each type of thinking, starting with Kahneman's own research on loss aversion. From framing choices to people's tendency to substitute an easy-to-answer question for one that is harder, the book highlights several decades of academic research to suggest that people place too much confidence in human judgment.

Source - Wikipedia

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Why talk about this book on this blog? Because it can explain, through the lens of Kahneman's research, biases in our thinking and understanding of extreme weather, flooding and climate change.

Kahneman's research helps explain to how the media, the public, and groups without scientific resources substitute an easy to answer question on meteorology for the harder ones on urban hydrology, infrastructure hydraulics, multi-objective decision making, extreme value statistics and risk assessment.  Here are some examples of the biases in thinking:

Heuristic biases

Anchoring or focalism is a cognitive bias that describes the common human tendency to rely too heavily on the first piece of information offered (the "anchor") when making decisions. In the context of extreme weather and climate change, most people have been exposed to well-documented temperature trend data for example from Al Gore in An Inconvenient Truth, and may use this "anchor" when making decisions about extreme rainfall trends (i.e., they assume historical rainfall trends are the same as temperature trends):

Exposure to temperature trend data anchors decision making on rainfall trends.  Exposure to trend data on annual rainfall (e.g., frequency of days with precipitation during a year) anchors decision making on frequency of short duration rainfall events that cause flooding - this is despite the fact that days with precipitation represents even minuscule 'trace' rainfall events (< 0.5 mm depth) while flood events typically require 100 times that threshold of rain (e.g., 50 mm depth).

Having weather personalities report that after extreme storms we had more than a month's rain in x hours, for example, anchors the public's perception about the frequency, or rarity, of the event when in fact a statistical evaluation of rainfall extremes would show that exceeding average summer monthly rainfall totals is not rare.

For example, after the July 8, 2013 storm in Toronto, where 126.0 mm of rainfall was recorded at Pearson Airport, the National Post reported "Before Monday, the highest rainfall ever experienced in Toronto for July 8 was 29.2 mm set in 2008 — a record that was more than tripled".  Tripling records sounds extreme when referred to a particular calendar day and anchors perception of rarity - but calendar days statistics are irrelevant given that summer convective storms are uncommon and 2/3 of July days are dry - furthermore daily totals of a similar magnitude were recorded twice before in 1980 and 1954 (119.9 mm and 137.4 mm respectively), and the previous July 8 record was exceeded by 200% in 7 other years between 1950 and 2013.  Headlines or course try to emphasize the rarity of events, not the commonplace.

In presenting Insurance Bureau of Canada and Institute for Catastrophic Loss Reduction's  "Telling the Weather Story" to the Empire Club in 2012 (YouTube) Dr. McBean first presents trends on temperature and discusses them for five minutes showing undeniable trends in warming, and warming rate - this anchors listeners.  He then switches to rainfall but shows no data, and instead only a theoretical bell curve frequency shift (see 13:10 in the video), but then concludes storm frequency is increasing as well. The listeners' cognitive bias due to anchoring on temperature will allow them to readily accept rainfall increases as facts as well, as opposed to recognizing rainfall increases as theoretical speculation as fully explored in this blog post and slide deck and in fact confirmed by Environment Canada and the CBC in response to inaccurate reporting.

The availability heuristic is a mental shortcut that occurs when people make judgments about the probability of events by how easy it is to think of examples.  In the context of extreme rainfall, 24-hour weather broadcasting, and 24-hour new channels give the public many example of flooding events that skew the perceived probability of occurrence. Hurricane Katrina and Hurricane Sandy are examples of extreme flooding that the public can recall in the context of flooding, but that have little relevance to urban flooding caused by convective thunderstorms. Likewise for Tsunamis.  Other types of flood events caused in large part by operational issues and inherent vulnerabilities are recalled and mistakenly associated with extreme rainfall as the sole cause (Union Station flooding June 1, 2012 was due to construction pump bypass capacity specifications, GO Train flooding July 8, 2013 due to rail line vulnerability (being below known moderate frequency flood levels)). 

Go Train Flood - Don River Floodplain - July 8, 2013

The availability heuristic leads to systematic biases, demonstrated in the judged frequency of repeated events.  It is irrelevant

Stranded GO Train in 1981 in same location as the
stranded GO Train in 2013 in the Don River valley.

that GO Train rail area flooding occurred on December 25, 1979, January 11, 1980, March 21, 1980, April 14, 1980, February 11, 1981 and May 11, 1981.  Under the availability heuristic people tend to heavily weigh their judgments toward more recent information, making new opinions biased toward that latest news. Nobody knows that the May 29, 2013 flood was worse (higher rainfall in East York, higher flow and flood levels at Todmorden gauge near the site) - because the train schedule missed the flood timing! Nobody remembers Ivan Lorant's flood inquiry report for Premier Bill Davis in the early 1980's.  Nobody asked the Toronto and Region Conservation Authority if this was a flood prone area and if this extent of flooding was unusual at the GO Train flood site. Nobody asked the Port Authority if the lack of Keating Channel dredging in the past few years contributed to flooding, just like it did in the early 1980's before the inquiry. 

Attribute substitution is a psychological process thought to underlie a number of cognitive biases and perceptual illusions. It occurs when an individual has to make a judgment that is computationally complex target attribute, and instead substitutes a more easily calculated heuristic attribute. This substitution is thought of as taking place in the automatic intuitive judgment system (System 1), rather than the more self-aware reflective system (System 2). Hence, when someone tries to answer a difficult question, they may actually answer a related but different question, without realizing that a substitution has taken place. This explains why individuals can be unaware of their own biases, and why biases persist even when the subject is made aware of them.

System 2 thinking about flooding must consider rain, runoff, flow and
flooding processes - a slow, effortful. complex and reliable approach.

As rain first causes runoff, which then creates flow, which then causes flooding, it is easy to mistakenly correlate increased flooding to increased rainfall.  The alternative is analyzing the complex problems of urban hydrology changes that influence runoff, the stormwater management mitigation measures that can lessen some impacts of some development at some scales, hydraulic interaction in the flow systems including riverine systems (Lisgar District Basement Water Infiltration Assessment is a wonderful example in Mississauga, or Basement Flooding Areas 4 and 5 in Toronto (see page 4 in the Executive Summary on Black Creek interaction)) with the overland, underground separated, combined and partially separated sewers, hydraulic impacts of operational constraints (bypass pumping during construction, inadequate dredging), hydraulic impacts of environmental protection measures (provincial F-5-5 compliance, federal Fisheries Act compliance, etc.), and hydraulic impacts of development intensification on overland flow routes and interactions with underground systems and private systems.  It is much easier to focus only on rainfall. And, conveniently, everyone has an opinion about the weather.

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Many prominent organizations and individuals have established a cognitive bias based on temperature trends and have since applied Kahneman's fast and error-prone System 1 thinking approach to rainfall extremes.  The anchoring bias in media report emphasizes the rarity / frequency of events and ignores past events and other causes (operational or intrinsic vulnerability) of flooding - Environment Canada's extreme rainfall frequency and trend data is ignored. The availability bias of extreme flooding events reported through the media skews the public's perception on the true probability of events - it is very easy to find examples of flooded underpasses because these are designed to lower flood standards, but flood a lawyer's Ferrari in an underpass and it will be ingrained in the public's mind for a long time. Attribute substitution bias allows the public to simplify and explain flooding with rainfall (rain = flood) as opposed to thinking about the actual complex system (rain = baseline runoff + development runoff +- mitigation measures = flow +- capacity constraints +- operational factors = flooding).

Media support attribute substitution by ignoring even the most fundamental physical facts. For example, the GO Train flood on July 8, 2013 was cited as a 2013 Top Weather Story by CBC News as they associated the record at Pearson Airport with the flooding (record rain somewhere = flooding somewhere else).  They ignored the fact that Pearson is in the Etobicoke Creek Watershed, three watersheds away from the Don River Watershed where the GO Train flooded - this is basic hydrology: Mississauga rain = runoff in Etobicoke Creek, not in Don River). They ignored that no record rainfall occurred in the Don River Watershed as they were anchored to the Mississauga data 25 km away.

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System 2 Mode of Thought -  Data and Analysis - Slow, Methodical.
Source: Environment Canada Engineering Climate Datasets ver 2.3.

Evidence-based policies require us to check facts: 

“There will still be times when someone accuses us of having lost our way, of having chosen the wrong priorities, and I know that can be hard to hear. But in moments in great and important choice, when the stakes are high, and the consequences are long-lasting, we have to test our assumptions.” Premier Kathleen Wynne, AGM, June 6, 2015 

System 1 Mode of Thought - Infographics and Heuristics - Fast, Emotional.
Source: Environmental Commissioner of Ontario,
Connecting the Dots on Climate Data in Ontario.

Testing assumptions requires Kahneman's "System 2" thinking - slow, deliberate and logical, as opposed to fast, instinctive and emotional in order to overcome heuristic biases in our thinking. 

Please. More Data.

Fewer Infographics.

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"People are not accustomed to thinking hard, and are often content to trust a plausible judgment that comes to mind."


Daniel Kahneman, American Economic Review 93 (5) December 2003, p. 1450



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Robert Muir's presentation on infrastructure adaptation to the WEAO OWWA Joint Climate Change Committee explores in significant detail the trends in Southern Ontario rainfall extremes that affect flood risk and that drive mitigation priorities:

Infrastructure Resiliency and Adaptation for Climate Change and Today’s Extremes from Robert Muir

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Tada! "Thinking Fast and Slow" themes in the above post have been expanded and are now published in the Journal of Water Management Modelling with the title "Evidence Based Policy Gaps in Water Resources: Thinking Fast and Slow on Floods and Flow":

https://www.chijournal.org/C449

Environment Canada Denies Change in Rainfall Events Over Past Decades

While there are many reasons to address climate change, increasing rainfall and resulting flood damages is not one of them.  Environment Canada, federal the agency responsible for collecting and analyzing weather data in Canada, agrees.  In response to a complaint on rainfall frequency reporting at CBC, Environment Canada has verified that there has been no significant change in rainfall events over several decades:

Excerpt. Environment Canada verifies no significant change

 in rainfall events over several decades.

Extreme rainfall reporting often goes like this, leading many to believe rainfall is increasing and leading to inaccurate reporting:

1) A convective summer thunderstorm drops 100 to 150 mm of rainfall over an urban areas that has been intensifying over decades (i.e., more runoff), and that can have drainage infrastructure constraints due to operational or structural changes (i.e., less flow capacity).

2) Flooding happens. 

3) Weather personalities share a characterization like "wow, we had a month of rain this afternoon folks", forgetting to mention that it doesn't rain much in the summer anyway and that 100 to 150 mm of rainfall is not an unusual event from an extreme value statistical point of view.

4) Many photos and videos are shared showing flooding in road underpasses, sometimes with expensive cars and stories about the owner - but the intrinsic built-in design vulnerability of underpasses in drainage design is not acknowledged.  (See 'subway' or 'depressed roadway' in MTO design criteria documents.  Or 'underpass' in Toronto design criteria.)

5) The insurance industry settles many flood claims at a great cost because it cannot distinguish if the event met policy restrictions, technically cannot characterize the neighbourhood scale factors that could exclude coverage, and perhaps legally cannot take the chance that unclear policy clauses on sewage back-up will not stand up in court if claims are denied.

6) There is no follow up discussion on the importance of runoff and how development intensification increases it, or that runoff mitigation measures are often sized to handle "smaller than extreme" events. (Public appreciation for hydrologic principles is very low, with focus group surveys suggesting many believe a 'watershed' is an building on the back lot for storing water.)

7) There is no follow up discussion on flow capacity and how it is constrained due to operational or structural changes to drainage and wastewater infrastructure. (This is a liability issue for the operator if the impacts of the changes were not carefully addressed.)  Also no follow up on the intrinsic vulnerability of underpasses which are sized by design, based on economic and technical constraints to handle only moderate storms and flows. (My experience is that capacity to handle a 100 year storm in an underpass, with 100 % redundancy in terms of back-up pumps, and stand-by diesel power, is rare - the depressed 400 series highway in Windsor may be the only one with this high level of service in the Ontario (i.e., Herb Gray /Windsor Essex Parkway).

8) Climate change modellers predict more extreme rainfall under some scenarios, despite having no models to simulate convective thunderstorms, and despite not using predictive models with a spatial or temporal resolution to analyze short term rainfall events (i.e., minutes and hours durations).  (The Ministry of the Environment in Ontario's expert panel indicated "Climate change science and modelling currently is not at a level of detail suitable for stormwater management where knowledge of the intensity, duration, frequency of storms and their locations and timing is required." - as per the report at this link)

9) People want answers and increased rainfall frequency or severity seems plausible, and besides, runoff discussions and flow capacity discussions are complex and not addressed.

10) Its 2015, and climate change temperature trends over years and decades are mistakenly considered to be the same as the short term extreme rainfall trends.

This is where we are today in the midst of an important discussion on climate change mitigation and carbon pricing.  Many climate change reports conflate temperature and rain.  Insurance industry conveniently points to rain as the reason insurance premiums are increasing, not saying how low investment returns by property and casualty insurers are forcing those companies to no longer subsidize underwriting activities as in past decades - that is increasing premiums.

Here are some resources and facts on the issues with today's rainfall frequency reporting:

1) Rainfall extremes happen.  Environment Canada publishes extreme value statistics as part of their Engineering Climate Datasets and exceeding "100 year storm" rainfall is not unusual.

• All the data is here: http://climate.weather.gc.ca/prods_servs/engineering_e.html
• It is a challenge to navigate but the intensity duration frequency files have information to show at each weather station when and how "100 year storms" were exceeded.  For example in Toronto's 61 year record at the Bloor Street gauge, we exceeded 100 year extremes in 1954, 1962, 1977, twice in 1986 (NB - neither August 19, 2005, not July 8, 2013 exceeded 100 years in downtown Toronto).

Excerpt from Table 1 Annual Maxium in file: idf_v2-3_2014_12_21_615_ON_6158355_TORONTO_CITY.txt
Version 2.3 data set for Ontario file: IDF_v2.30_2014_12_21_ON.zip

• Rainfall intensity for duration of interest that cause flooding in urban areas is not increasing as Environment Canada has verified in response to our complaint on inaccurate reporting in this story :

Excerpt. CBC confirms Environment Canada has verified no change in rainfall over decades..

• Here is our summary of Canada-wide rainfall trends in the Engineering Climate Dataset which shows for 565 weather gauges :
  • there is no statistically significant change in rainfall intensity for 86% of data points
  • there is a statistically significant decrease for 2 to 3% of data
  • there is a statistically significant increase for 3 to 5% of data
  • there is incomplete data for trend analysis 7% of the time
  • for shortest duration rainfall that affects urban flooding, just less than 3% of data shows increases in intensity (5 minute intensity increases at 2.7% of gauges)
   

  

  Real climate data from Environment Canada shows no change in historical rainfall intensities.
  Trend data file used: idf_v2-3_2014_12_21_trends.txt
  From Environment Canada's file: IDF_Additional_Additionnel_v2.30.zip

2) Flooding happens when rainfall extremes exceed the design capacity of our drainage systems and because those systems are becoming more and more constrained.

• Underpasses are designed for 10-year to 25 year storms in some cases (check the Toronto criteria here in the design standards).
• Over a many years, underpasses have a high risk of flooding, for example, sized for a 10-year storm flood frequency there is a 41.0% chance of flooding in 5 years, or sized for a 25-year storm there is a 33.5% chance over 10 years.  This is a nice summary table of risks: 

Source : Reference Guide for Applying Risk and Reliability-Based Approaches for Bridge Scour Protection,
NCHRP Report 761, 2013.

• The Don River floodplain that floods the Don Valley Parkway in Toronto and that flooded the GO Train rail line on July 8, 2013 floods because of an intrinsically low design capacity.  Or put another way, there is inadequate "freeboard", or buffer, between the elevation of the travelled lanes and rail bed and the moderate and extreme water levels of the river.
• The 1981 inquiry into Toronto's Don River flooding sheds light on past railway flooding, including the area of the infamous GO Train flooding on July 8, 2013.  The 81 page report is available at the Toronto Reference Library:
  http://www.torontopubliclibrary.ca/detail.jsp?Entt=RDM209381&R=209381

• The inquiry report provides a chronology of 40 Don River flood events during both ice-jam and ice-free conditions dating back to spring 1801 when aboriginals could not spear fish for salmon due to the post-flood high turbidity levels.  Railway line damage and flooding during ice-free conditions (i.e., no ice blockage of bridges) was reported in the "Great Flood" on September 13, 1878, the spring of 1914, and during two storms in 1980 (March and April).  Limited flooding was also reported on May 11, 1981 including the area of the Bayview Extension and the Toronto Brick Yards - the stranded GO Train incident occurred was just south-west of the Brick Yards (now the Evergreen Brick Works).  The report indicates that train operation has halted, or trains were detoured during floods, including December 25, 1979, January 11, 1980, March 21, 1980, April 14, 1980, February 11, 1981 and May 11, 1981.

3) After extreme events weather personalities / presenters compare weather extremes to climate "normals", or averages, which exaggerates the severity of the storm event.

• Environment Canada publishes normals including average monthly rainfall amounts are low in the summer.  For example, in Toronto the average rainfall for July is 63.9 mm, as shown below or at this link

• The rainfall statistics for Toronto show that even a moderate frequency "10 year storm", with 67.6 mm of rain over a day, exceeds the monthly average by 6%.  So why would we be surprised that some more extreme storms exceed the monthly total - as noted above, there is 41% chance we will have a 10 year storm every five years?

  

  Table 2a Return Period Rainfall Amounts (mm) in file: idf_v2-3_2014_12_21_615_ON_6158355_TORONTO_CITY.txt
  Version 2.3 data set for Ontario file: IDF_v2.30_2014_12_21_ON.zip

Nobel Memorial Prize in Economics winner Daniel Kahneman explains why humans struggle to think statistically. We substitute heuristics for methodical thought.  So an evaluation of infrastructure vulnerabilities is not within our capabilities in many cases - please see our next post for an exploration of heuristic biases that can influence reporting on extreme rainfall, flooding and climate change.

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Extreme rainfall trends in Canada (Environment Canada Engineering Climate Datasets) are documented in the following posts:

Static Maps: http://www.cityfloodmap.com/2015/12/severe-storm-trends-canada-rainfall.html

Interactive Map: http://www.cityfloodmap.com/2015/12/canadian-extreme-rainfall-map-climate.html

Table Summaries: http://www.cityfloodmap.com/2015/12/canadian-extreme-rainfall-summary-by.html

Chart and Table: http://www.cityfloodmap.com/2015/12/top-weather-story-in-canada-2015-less.html

Long-term Station Table: http://www.cityfloodmap.com/2015/12/long-term-climate-change-short-term.html

Environment Canada Denies Changes: http://www.cityfloodmap.com/2015/10/bogus-statements-on-storms-in-cbcnewsca.html

Contradicting Insurance Industry Claims: http://www.cityfloodmap.com/2015/12/trends-in-canadian-shortduration.html

Ontario Climate Change Policy - Minister Murray Ignores Rainfall Data, Conflates Climate and Weather

No real change in Canadian rainfall extreme weather.
Environment Canada's Engineering Climate Datasets v2.3.

Below is CityFloodMap's response to the brief CBC report on the Ontario government's climate change plan. The leaked cap and trade plan would not go ahead if these facts were considered:

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Murray said severe weather events have cost the government hundreds of millions. But Environment Canada verified no significant change in rainfall events over decades: 

http://www.cityfloodmap.com/2015/07/storm-intensity-not-increasing-old.html 

CBC has corrected their earlier reporting on storm trends as a result of these facts: 

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

Don't "Blame it on the Rain" like MiIli Vanilli because there are other factors that quantitatively explain increasing flood damages in Ontario as in my letter to the Minister: 

http://www.cityfloodmap.com/2015/08/letter-to-ontario-minister-of.html 

Evidence-based policies require us to check facts: 

“There will still be times when someone accuses us of having lost our way, of having chosen the wrong priorities, and I know that can be hard to hear. But in moments in great and important choice, when the stakes are high, and the consequences are long-lasting, we have to test our assumptions.” Premier Kathleen Wynne, AGM, June 6, 2015 

Now is a good time. The insurance industry has been off base for several years on rainfall facts and is WAY out of step with Environment Canada data. Milli Vanilli's step aside: 

http://www.cityfloodmap.com/2015/11/milli-vanilli-blame-it-on-rain.html 

The GO Train rail line has flooded for centuries and decades as reported in the flood inquiry report to Premier Davis (Keating Channel dredging is behind schedule): 

http://www.cityfloodmap.com/2015/07/go-train-flooding-not-new-1981-inquiry.html 

Its time to start connecting to dots on climate change and have Ontario graduate from infographics and spin, and to real science and real evidence based policy: 

http://www.cityfloodmap.com/2015/07/connecting-dots-on-climate-change-100.html

Premier Kathleen Wynne and Ontario Ministers of the Environment and Climate Change, Natural Resources, Infrastructure, Municipal Affairs and Housing, its time to 'slow down the thinking' on extreme weather (a la Daniel Kahneman) and overcome heuristic biases:

http://www.cityfloodmap.com/2015/11/thinking-fast-and-slow-about-extreme.html

The Ontario Chamber of Commerce should demand that Ontario govenment look at the big picture and misstatements on climate change impacts. If it did, it would realize that it should be investing in Design Standard Adaptation and funding municipalities to address flood risks, and not be tilting to windmills (err.. turbines) as a means of Climate Change Mitigation - detailed analysis of flood causes supports a more focused and rational approach to flood issues in Ontario:

http://www.cityfloodmap.com/2016/04/design-standard-adaptation-vs-climate.html

Bogus statements on storms in cbcnews.ca report - 'twenty times more storms' in Windsor-Essex

Update: CBC has updated their story in response to our complaint on the accuracy in the original news report.  Thank you for listening CBC Windsor.  Here is the clarification offered:

Clarifications

• This story has been updated to include comment from Environment Canada on heavy rainfall events in the Windsor region.
  Nov 20, 2015 12:06 PM ET

The highlighted text below has been added to the report.  Note, we provided information to CBC on rainfall trends between 1946 and 2009 as shown below, and it appears Environment Canada has also reviewed trends from 1953 to 2012 to respond to the complaint :

"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."

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.

It appears that the interviewee based statements on an insurance industry newsletter.  

Excerpt. CBC response to complaint on storm statistics and frequency causing flooding.

****** Updated Post Below *******

(Originally) no fact checkers at cbcnews.ca this week for a story on storm frequency.  Hence bogus statements  introduce an article on why storm damage claims are increasing:

"The more storms Mother Nature dishes out, the more problems homeowners have with their sewers and basements.

And with an increasing frequency of storm events, insurance companies serving homeowners in Windsor and Essex County are taking a harder line on what coverage they can offer and what their customers must pay to receive it."

And the interviewee seems to back this up by doubling down:

"On a statistical basis ... "we're getting 20 times more storms now than we were 20 years ago.""

Well this embodies the quote about there being lies, damn lies and statistics, because the true statistics on rainfall frequency shows the opposite in Windsor-Essex, from whence many a Tecumseth tall tale teller hail.  Environment Canada statistics show us decreasing intensities - i.e., REAL downward trends in annual maxima for rainfall volumes over a range of durations from 5 minutes to 24 hours. 

This data is freely available to anyone with an internet connection, and is readily applied by those water resources engineers and municipal drainage designers who work with rainfall statistics as part of their professional practice.  Certainly, storms did not increase twenty times and storms cannot explain the change in insurance claims over the past decades.  Storm intensities are decreasing at the Windsor Airport gauge (station ID 6139525) since the mid 1940's (CBC has clarified through Environment Canada correspondence that "there has been no significant change in rainfall events over several decades").  Other possible factors affecting damages:

1) Runoff increased due to development

2) Overland drainage systems have been compromised

3) More expensive stuff in basements

No doubt cbcnews.ca needs better fact checking (some fact checking?).  There is no QA/QC in reporting on extreme weather in Canada.  Sad.  It took all afternoon to summarize the trends in rain intensity for climate stations across Canada in one simple graph, but its not hard to do because Environment Canada does the trend analysis on the raw data and categorizes trends as significantly significant or not in their publications - this summary of rain intensity trends is for 565 stations:

Real climate data from Environment Canada shows no change in historical rainfall intensities.

 The statistics for 565 weather gauges show us the following:

• there is no statistically significant change in rainfall intensity for 86% of data points
• there is a statistically significant decrease for 2 to 3% of data
• there is a statistically significant increase for 3 to 5% of data
• there is incomplete data for trend analysis 7% of the time
• for shortest duration rainfall that affects urban flooding, just less than 3% of data shows increases in intensity (5 minute intensity increases at 2.7% of gauges)

If the rainfall frequency distribution is stationary (no change), after a long, long time, half of gauges would have increases and half decreases.  Looking at all data points including the non-significant trends what are the changes? :

• 41% of data showed a decrease in intensity
• 52% of data showed an increase in intensity
• 7%  of data was incomplete (no data trend)

So it is not like there are a lot of increases just shy of statistical significance ... its a fairly even split for a random sample. I redid the analysis screening out rain gauge records shorter than 20 years (the data above was 10+ years) and using only gauges whose record ended in since the year 2000 to focus on newer data and more long-term reliable records.  For these screened 345 gauges we find more or less the same:

• 42% of data showed a decrease in intensity
• 56% of data showed an increase in intensity
• 2%  of data was incomplete (no data trend)

So has Mother Nature dished out more rain, or have developed municipalities dished out more runoff over the decades?  Saying there are 20 times more storms than there were 20 years ago is just plain wrong - in fact it is a 'worse-than-useless' statement because it diverts attention from real risk factors and effective management approaches.  Canada needs evidence-based policy on flood risk management and open data to support better decision making.  The real Environment Canada data is available for download here:

http://climate.weather.gc.ca/prods_servs/engineering_e.html

Environment Commissioner of Ontario infographic non-data

The cbcnews.ca data  is available in the Government of Ontario infographic at right.  Notice there is no real data there, no labels on the access, no data sources, nothing really.  But it seems quite definitive with the exclamation point and all.

Further Government of Ontario climate data is available in the rubber-chicken graph below, because data does not matter to those who do not believe in evidence based policy, science, statistics, or informed decision making.

Government of Ontario climate data.  Oh my, it is getting big and scary just like the infographic and cbcnews.ca foretold!