University of Guelph Research Shows Lower Spring Flooding With Global Warming, No Change in Rainfall, and Explains Urban Flooding Due to Urbanization - Not Climate Change Effects

Research from the University of Guelph has shown that climate change has reduced spring flooding risk (exponential growth in frost-free days with more recharge and less snow pack / spring melt) and that summer flow changes are due to urbanization, not changes in precipitation.

The presentation below summarizes the research and is entitled "Disentangling Impacts of Climate & Land Use Change on Quantity & Quality of River Flows in Southern Ontario" - the authors, Trevor Dickinson and Ramesh Rudra from the University of Guelph clearly see the need to clarify drivers for flow changes and to avoid the common media mistake of associating all extreme hydrologic conditions with climate change and omitting changes that may lower risks (like spring flooding in some watersheds).



Research indicates:
1) Monthly and Annual Precipitation has remained unchanged (see slide 7)
2) Temperatures have risen 'mostly in the winter' (see slide 13 - 14), meaning summer maximum temperatures that are typically associated with extreme rainfall have not increased, or have decreased
3) Extreme daily maximum temperatures have decreased (slide 14)
4) Increased winter temperatures mean more steady winter runoff, more infiltration and "Decreased Snowmelt Floods" (see slides 24 - 31)
5) Urbanization increases runoff coefficients (slide 36-37) and:

" So … in Ontario urban watersheds: - urban development has augmented the winter and spring climate change impacts; and - summer flow volumes have increased dramatically, in volume and frequency, these impacts being completely due to urban development."

The big take away is that urbanization is a key driver for summer river flows in Southern Ontario, but climate change is not - this is supported by trends in the Engineering Climate Datasets (version 2.3) that show twice as many statistically significant decreasing Southern Ontario trends as increasing ones.

This analysis is consistent with review by others showing change in minimum temperatures but no change in summer maximum temperatures. For example, the Ontario Centre for Climate Impacts and Adaptation Resources reviewed climate change trends for several stations - for Ottawa airport, between 1939 and 2014, the average winter minimum is up by 2.5 degrees Celcius and average winter mean is up 2.2 degrees. But the summer maximum is flat - no change. While the summer mean temperature is up by 0.5 degrees, this is due to increases in minimum temperatures, which were up by 1.1 degrees. These graphs from the Centre show the difference in winter temperatures changes and summer temperatures changes:

Winter temperatures have increased with climate change - Ottawa, 1939-2016

Summer maximum temperatures (middle chart) have NOT increased with climate change - Ottawa, 1939-2016. Changes in mean temperature are driven by changes in minimum temperatures.
Those who point to the Clausius-Clapeyron equation and a greater water vapour holding capacity at higher temperatures as a driver for climate change-induced flooding in urban areas should reevaluate their position, and consider the data on maximum temperatures. Since there is no increase in summer maximum temperature at some stations, the cause of flooding due to extreme rainfall cannot be greater water vapour holding capacity of the air - as research at the University of Guelph has shown, urbanization and not climate change is the key driver for changes in river flow. We can expect the same types of flow impacts beyond river systems and within municipal infrastructure systems, where urbanization and intensification have increases hydrologic stresses on systems even with no change to rainfall inputs.

The Ontario Centre for Climate Impacts and Adaptation Resources reviewed climate change trends for Hamilton as well. The following charts show the same relative temperatures changes as Ottawa:
Hamilton winter temperature has increased the most due to climate change.

Hamilton summer temperatures have increased at only a fraction of the winter increase.
 The Hamilton summer maximum temperatures increase (0.4 degrees in 40 years from 1970 to 2010) is only a fraction of the winter maximum increase (1.8 degrees in 40 years). The 0.4 degree increase in summer maximum would translate into less than a 3% change in water vapour holding capacity over 40 years. A review of research in another post has shown that temperature increases have not resulted in extreme rainfall increases across Canada - see post here.

Urbanization has increased significantly in Southern Ontario since the mid 1960's as shown in this post - this includes Hamilton growth:



In the Toronto area, where the University of Guelph assessed changes in runoff and linked these to urbanization as opposed to climate change, growth has also been significant since the mid 1960's. The following table shows changes in Toronto-area watersheds where urbanization increased from 59% to 986% over a perido of about 35 years. Compared to theoretical temperature-induced water vapour changes changes of a few percentage, if any at all, urbanization clearly explains higher runoff stress and flood risk while climate change explains none of the risks.

Urban Growth in TRCA watersheds and Flood Risk Influence on Urban Flooding

Greater Toronto Area Urban Area Growth in TRCA watersheds and Flood Risk Influence on Urban Flooding

Climate Change and Infrastructure Resiliency Assessment - What Representative Concentration Pathways Should be Used to Estimate Future IDF Curves? Caution Using RCP8.5.

There is considerable uncertainty in modern infrastructure design methods when rainfall design intensities are well established using past observations and derived return period values. The uncertainties include:

1) runoff coefficients or other hydrology parameters, especially for pervious surfaces
2) catchment response time (time of concentration), typically estimated using empirical methods
3) rainfall temporal pattern, aka design storm hyetograph, derived from input IDF data (for hydrologic and hydraulic simulations) ... and the spatial pattern which is always ignored because it is chaos
4) hydraulic performance of inlets and grates
5) hydraulic roughness and energy losses in junctions, etc.

Considering future climate scenarios, the input IDF is also uncertain. Estimated future values often depend on the assumed Representative Concentration Pathway (RCP) which are called 2.6, 4.5, 6.0 and 8.5 and which represent progressively more extreme emissions, CO2 concentrations, and energy entering the troposphere (the number 2.6 represents the energy per area warming the planet you could say).

Future design IDF estimation tools like the University of Western IDF_CC Tool give a choice of 3 pathways - 2.6, 4.5 and 8.5. The description of RCP 8.5 indicates that this scenario gives the most severe climate change impacts as noted below. But the extreme intensities do not always support that statement.


The following future IDF intensity tables for RCP2.6, RCP4.5 and RCP8.5 show that the RCP4.5 scenario can give the highest short duration intensities that affect infrastructure capacity and resilience. The 5-year 5-minute intensity is highest for RCP8.5 but only 3.5% above RCP4.5, which is very small in the context of infrastructure design. But the 100-year 5-minute intensity for RCP8.5 is below the RCP4.5 values by over 8% - and the 24-hour intensity is also about 8% lower. So RCP8.5 is not the most conservative, 'most severe' scenario for extreme 100-year events. Note these tables are based on a period of 2050-2100.




The reasonableness of the RCP8.5 has been questioned. In Energy, University of British Columbia note “RCP8.5 no longer offers a trajectory of 21st-century climate change with physically relevant information for continued emphasis in scientific studies or policy assessments.” Researchers add:

"This paper finds climate change scenarios anticipate a transition toward coal because of systematic errors in fossil production outlooks based on total geologic assessments like the LBE model. Such blind spots have distorted uncertainty ranges for long-run primary energy since the 1970s and continue to influence the levels of future climate change selected for the SSP-RCP scenario framework. Accounting for this bias indicates RCP8.5 and other ‘business-as-usual scenarios’ consistent with high CO2 forcing from vast future coal combustion are exceptionally unlikely. Therefore, SSP5-RCP8.5 should not be a priority for future scientific research or a benchmark for policy studies."

Because there is such as wide range of future IDF possibilities already, it is good to know that RCP8.5 could be discounted as implausible in sensitivity analysis. The chart below shows various projections for 5-minute 100-year rainfall intensity for a range of RCP scenarios. Dropping RCP8.5 from further consideration will help focus assessments of infrastructure resiliency. But considering RCP4.5 may yield even higher IDF values than the assumed 'most severe' RCP8.5 scenario.

IDF climate change Ontario Canada
Future IDF Uncertainty - Moving Target Under Various Representative Concentration Pathways

RCP2.6 scenarios may not result in future IDF intensities that are above current design standard values as shown in the chart above.

TVO Articles on Climate Change, Extreme Rainfall and Urban Flooding Omit Basic Fact Checking and Ignore Fundamental Engineering Principles

I have posted comments on three TVO Articles on the topic of climate change, extreme weather, urban flooding and resiliency of Ontario Cities. Readers of this blog will be familiar with the content. It gets a bit repetitive from article to article, only because the data gaps are the same old ones we always see on these topics.

1) How climate change is making storms more intense, Published on Apr 21, 2017 by Tim Alamenciak

https://tvo.org/article/current-affairs/climate-watch/-how-climate-change-is-making-storms-more-intense

My Comments:
This is absolutely incorrect. Environment and Climate Change Canada (ECCC) published in Atmosphere-Ocean in 2014 that there is "no detectable trend signal" in the Engineering Climate Datasets related to short-duration rainfall that causes urban flooding:


Windsor has the lowest level of service for floodplain protection (100 year storm) while other regions have Hurricane Hazel (over 500 year storm) - so Windsor / Essex region will flood a lot more that other places. Also Windsor has been effectively tightening up their sanitary sewers to prevent spills to the river (reduced combined sewer overflows (CSOs)) which means more stays in the sewers and can back-up basements in extreme weather. Its a tough trade-off when environmental protection (keeping sewage out of the river) means more sewage in basements.

This is a recent summary of ECCC data as well as studies my Ontario universities and major engineering consultants saying decreases in extreme rainfall in Ontario. In fact there are twice as many statistically significant decreasing trends as increasing ones in southern Ontario (per the version 2.3 Engineering Climate Datasets - links to ECCC data files are all provided on the slides:


This presentation to the Ontario Waterworks Association and Water Environment Association of Ontario's Joint Climate Change Committee does extensive myth-busting related to extreme rainfall and flooding and explore the true drivers to increased flood events (spoiler-alert: its engineering hydrology and hydraulics, not meteorology). It also shows how the Clausius-Clapeyron relationship (theory relating temperature to extreme rainfall) has been disproved by research at MIT, Columbia and the University of Western. Unfortunately, there are lot of opinions and high level statements that are made without data. This is a pervasive problem in the media. When fact checking does occur, Advertising Standards Canada, the CBC Ombudsman and Canadian Underwriters have all agreed that there is no change to extreme rainfall. Here are some examples of that:

More data / facts / details:

Windsor decreasing extreme rainfall trends (Engineering Climate Datasets version 2.3 Station ID 6139525) - decreasing for ALL storm durations, and statistically significant decreases for durations of 10 minutes, 2 hours, 6 hours and 12 hours:


CBC Ombudsman confirms with ECCC, and disputes insurance industry statements that we have more storms (see letter to me):

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

That was in response to this story that had no fact-checking:


And which had this correction made based on ECCC and real data: "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." Canadian Underwriter editors dispute insurance industry statement on more frequent / severe storms after fact-checking with ECCC:


"Associate Editor’s Note: In the 2012 report Telling the Weather Story, commissioned to the Institute for Catastrophic Loss Reduction by the Insurance Bureau of Canada, Professor Gordon McBean writes: “Weather events that used to happen once every 40 years are now happening once every six years in some regions in the country.” A footnote cites “Environment Canada: Intensity-Duration-Frequency Tables and Graphs.” However, a spokesperson for Environment and Climate Change Canada told Canadian Underwriter that ECCC’s studies “have not shown evidence to support” this statement."

We can explain most increased flooding by hydrological changes over the past 100 years (same rain a before but more runoff than before as urban areas have expanded drastically across GTA watersheds over the past 60 years):

http://www.cityfloodmap.com/2016/08/urbanization-and-runoff-explain.html

... and specifically here is are the changes in hydrology in southern Ontario cities including the Windsor area:


We can also explain increased flooding with hydraulics related to municipal drainage design (tanks to hold back water and protect beaches can back up into basements like in my Toronto "Area 32" engineering flood study report), and related to overland flow in 'lost rivers' that statistically explain the highest concentrations of reported basement flooding:


Basically, hydrologic stresses have increases (more runoff) and conveyance capacity has decreased (reduced CSO relief, tanks to protect beaches, blocked overland flow paths in old 'lost rivers'). Underpinned/excavated basements are now lower than before, closer to the crown of the sewer pipes in the street and more prone to sewage back-ups than before, with no change in rainfall extremes due to climate change.

Robert J. Muir, M.A.Sc., P.Eng.

Toronto


2) How climate change is already costing you money, Published on Nov 01, 2017 by Patrick Metzger

https://tvo.org/article/current-affairs/climate-watch/how-climate-change-is-already-costing-you-money

My Comments:

There are many false statements in this article and a lack of basic science, statistics or critical engineering considerations. I am a licensed Professional Engineer with extensive experience in extreme weather statistics and municipal infrastructure planning and design (26 years) - this article is like 100's of others, skimming the surface and missing the critical data and conclusions, reinforcing stale pundit talking points in the climate-change-echo-chamber. Please see below for what is wrong with the article.

Firstly, the article conflates climate and weather which have different temporal scales. Climate includes rainfall and precipitation over seasons, years and decades while weather related to flooding in urban areas involves rainfall over minutes and hours. So the cited increase in precipitation is irrelevant to urban flooding and insurance since precipitation trends over months and years do not govern the performance of infrastructure systems (storm sewers, sanitary sewers, drainage channels and overland flow paths) - that infrastructure is governed by extreme rainfall rates over minutes and hours. It is an undeniable engineering fact. And these short duration rainfall intensities are 'flat' across Canada according to Environment and Climate Change Canada, as published in Atmosphere-Ocean in 2014 - in fact ECCC stated that some regions have decreasing trends including the St Lawrence basin in Quebec and the Maritimes.

My own fact checking of the Engineering Climate Datasets (version 2.3 on the ECCC ftp site) shows twice as many statistically significant decreases in southern Ontario as increases, and for the critical shortest durations, no statistically significant increases at all. Here is a review of the typical insurance industry statements and the real data:


Over the past two weeks I have correspondence from 3 scientists at ECCC stating that the annual precipitation statistic (climate) is irrelevant to urban flooding and the short duration rainfall (extreme weather) is what we should be looking at - across Canada the relevant data shows 'no detectable trend signal'. TVO should check the background of those providing information for these articles to see if the academic and practical experience aligned with the technical topic being discussed.

It is too easy to just try and may headlines and exercise 'availability bias', 'anchoring bias' and other problem-solving short cuts with discussing extreme weather and flooding. It is more responsible to look at real data and fact-check articles because there is important public policy on climate adaptation and mitigation that relies on the proper characterization of the problems that we are solving. Blaming flooding on rainfall trends misdirects resources to mitigation when it should be focused on adaptation to yesterday's extremes (due to intrinsic design limitations in 50-100 year old infrastructure and land use planning). Chief economists at major banks have repeated IBC statements on extreme weather shifts with no fact checking whatsoever - the Sun, the Star, CBC and individual insurance companies have repeated it too without checking. They have been fact checking with ECCC recently though and the consensus is that there is no shift in extreme rainfall and IBC mixed up a theoretical future shift (of an arbitrary 'bell curve' no less) and had reported it extensively as a past observation by ECCC. ECCC has denied that their data shows any increase in severe weather with climate change.

Some examples of ECCC refuting insurance industry claims:

Ombudsman confirms with ECCC, and disputes insurance industry statements that we have more storms (see letter to me):


That was in response to this story that had no fact-checking:

http://www.cbc.ca/news/canada/windsor/more-than-half-of-homeowners-insurance-claims-stem-from-water-damage-broker-says-1.3291111

And which had this correction made based on ECCC and real data: "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."

Canadian Underwriter editors dispute insurance industry statement on more frequent / severe storms after fact-checking with ECCC:


"Associate Editor’s Note: In the 2012 report Telling the Weather Story, commissioned to the Institute for Catastrophic Loss Reduction by the Insurance Bureau of Canada, Professor Gordon McBean writes: “Weather events that used to happen once every 40 years are now happening once every six years in some regions in the country.” A footnote cites “Environment Canada: Intensity-Duration-Frequency Tables and Graphs.” However, a spokesperson for Environment and Climate Change Canada told Canadian Underwriter that ECCC’s studies “have not shown evidence to support” this statement."

Lastly, the Clausius-Clapeyron relationship linking temperature to extreme rainfall have been shown to not hold up based on real observed data. This is a review of those findings in studies from MIT, Columbia and University of Western (in London and Moncton trends are flat, while in Vancouver there is less extreme rainfall at higher temperatures):


Its time for a lot more basic fact checking on climate change, extreme weather and flooding. There is too much 'thinking fast' and not enough 'thinking slow', as shown in this review of media reporting biases through the lens of Kahneman:

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

Unfortunately, as Kahneman puts it ""People are not accustomed to thinking hard, and are often content to trust a plausible judgment that comes to mind.", American Economic Review 93 (5) December 2003, p. 1450

"Only the small secrets need to be protected. The big ones are kept secret by public incredulity."(attributed to Marshall McLuhan) .. .so true, especially when we rely on infographics and slogans and ignore basic data in our reporting.

Robert J. Muir, M.A.Sc., P.Eng.
Toronto


3) How Ontario cities battle climate change, Published on Dec 01, 2015 by Daniel Kitts

https://tvo.org/article/current-affairs/the-next-ontario/how-ontario-cities-battle-climate-change

My Comments:

Mr Adams is correct is questioning Mr Kitts 'facts'. Because the official national Engineering Climate Datasets show no detectable trend in extreme rainfall in Canada. This was published in Atmosphere-Ocean in 2014 and looks at the critical short duration rainfall rain intensities that drive urban flooding. Here is a review that explore that national data in detail, drilling down to Ontario and southern Ontario trends and showing why insurance industry statements on higher weather frequency shifts were exposed to be 'made up' (confusing arbitrary future predictions with past observations):


Citing IPCC is irrelevant in the context of urban flooding in Ontario cities .. IPCC's definition of 'heavy rainfall' is the 95% percentile of daily rain with in Toronto is about 29 mm of rain - that is big for 'climate' but tiny for 'weather'. Typically storms have to be 3 times that big to cause urban flooding and most new communities are designed to handle 100-year design storms with built-in resiliency measures / safety factors to handle larger storms (if we see a hockey stick and get more extreme rain in the future).

Recently I made presentation to the Ontario Waterworks and Water Environment of Ontario's Joint Climate Change Committee on city resiliency and adaptation. In it there is wealth of basic media myth-busting many would benefit from. It includes explanations of why we have more flooding from a quantitative engineering perspective, exploring hydrologic stresses and intrinsic hydraulic design limitations in 50-100 year old infrastructure and land use planning:


It shows for example that 2017 Lake Ontario levels, while above average, were not very extreme looking back at 100 years of record (we exceeded past records by about 5 cm in some months which is naturally what happens with longer and longer records and the updated operating 'rule curves' for the lakes). It shows that the Richmond Hill GO Train was flooded in 1981 (just like 2013) in the exact same spot, even though the Ontario government suggests the 2013 flood was due to climate change. It shows that during the highest short duration rainfall recorded in Toronto in 1962 there was extensive basement and roadway flooding (this is not a new phenomenon at all). It shows numerous studies at the University of Guelph, University of Waterloo and major engineering consultants that Ontario extreme rainfall in decreasing and that extreme rainfall is not coupled to temperature changes. It shows significant urbanization in Oakville, Burlington and the rest of the Golden Horseshoe wince the 1960's and how we have paved up to the upper limit of the Burlington escarpment headwater watershed in that time - its hydrology that explains the increased flooding, not meteorology! This blog post shows the drainage paths in Burlington a little better than the OWWA WEAO presentation at the link above:


These change in hydrology and runoff potential are undeniable and dwarf any noise in the extreme rainfall statistics. The 'new normal' is in fact the 'old extremes' that we have always had .. the system response is more severe however with greater runoff into the same 50-100 year old infrastructure and confined channels along the lower portions of our watersheds. When it comes to urban flooding, only Milli Vanilli 'Blame it on the Rain'. Nobody cares about hydrology. Canada's greatest hydrologist Vit Klemes once lamented about this saying If you have not read it, please see his key note address to International Interdisciplinary Conference on Predictions for Hydrology, Ecology, and Water Resources Management: Using Data and Models to Benefit Society, entitled "Political Pressures in Water Resources Management. Do they influence predictions?"


Basically you could say that today on Ontario it is not unlike the communist Czech Republic that Dr Klemes describes in his address, where predictions (climate change) becomes prescriptions, despite the facts and data. And the media is so far out of touch that we cannot put the
genie back in the bottle and the government is playing along pretending to help solve problems while ignoring true causes.

As our Dr Klemes spoke in Prague:

"[the theorists] find it easier to play trivial scenario-generating computer games while the [managers] find these games much easier to finance... And so by happy collusion of interests, an impression is created that 'something is being done for the future' while the real problems are quietly allowed to grow through neglect of the present"

That is 100% correct. We are ignoring the present risks of today related to hydrology and blaming our flood problems on a climate change computer game (Weather Zoltar if you will). RIP Dr Klemes .. I still remember your guest lecture in our undergraduate class and wish you were around to speak truth to power on this topic.

TVO you have to raise the bar on this topic and demand basic fact checking especially given ECCC statements, corrections by Advertising Standards Canada, CBC Ombudsman, Canadian Underwriters ....

Robert J. Muir, M.A.Sc., P.Eng.
Toronto

Radical Transparency. Uncovering the 'big secrets' in urban flood risk adaptation and extreme rainfall trends under climate change in Southern Ontario.

"Truth and untruth exist at the same level of authority on the internet."
Salman Rushdie, on Fareed Zakaria GPS, September 17, 2017

"Only the small secrets need to be protected. The big ones are kept secret by public incredulity."
Marshall McLuhan

Too bad. Lets expose the big secrets in flood risk management and climate adaptation, and give truth the upper hand, shall we?

Lets encourage "radical transparently". Why? So that we can create data-driven, evidence-based policies to cost-effectively manage flood damages and reduce risks to people and property.

This radical transparency is promoted by Ray Dalio, founder of Bridgewater Associates (see his Ted Talk here on successful investing and company building). Dalio says that to be successful we need to "bet against the consensus" and "be right".

The presentation below on the key drivers for managing flood risk in Southern Ontario goes against the consensus in terms of extreme weather extremes (showing they are down not up) - but its not a bet, but rather a careful review of data - so in that regard I trust it is 'right' .... or certainly right-enough for its intended purpose given all the other uncertainties in hydrology and hydraulic disciplines.




Ray Dalio in his Ted Talk shares his painful "Fail Forward" moment of ruin and how he used the experience to improve his decision making. He said "Rather than thinking 'I'm Right', I started asking myself 'How do I know I'm Right?' I gained a humility I needed in order to balance with my audacity. I wanted to find the smartest people who would disagree with me to try to understand their persepctive or to have them stress test my perspective. I wanted to create an idea meritocracy ..."

Let me know your thoughts. I welcome any 'stress test' of my OWWA WEAO Joint Climate Change Committee presentation above. Thank you so much!

R. Muir

Less Extreme Short Duration Rainfall in Kitchener-Waterloo - IDF trends do not show climate change impacts that would affect urban flooding.

The University of Waterloo civil and environmental engineering department analyzed design rainfall intensity trends - that is intensity-duration-frequency (IDF) statistics used in infrastructure design - with the goal of potentially updating City of Kitchener and City of Waterloo design rainfall values. Why do this? Because climate change is predicted in some models to increase the intensity and frequency of extreme rainfall. Results are in the following report:

Update of Intensity-Duration-Frequency (IDF) Curves for the City of Waterloo and the City of Kitchener Prepared By: Donald H. Burn, Ph.D., P.Eng. Department of Civil and Environmental Engineering University of Waterloo, August 2012.

The executive summary states there is no significant change and some decreasing trends for short duration rain intensities - that is, the design parameters that affect urban infrastructure flood risks:

"Annual maximum rainfall data for durations ranging from five minutes to 24 hours were analyzed for trends using the Mann-Kendall non-parametric trend test. Although no statistically significant trends were identified, there were noticeable patterns in the magnitude and direction of the trends in the rainfall data, as a function of the rainfall duration. Based on the available rainfall data for the period 1971 to 2007, new intensity-duration-frequency (IDF) curves were developed for the Waterloo Wellington A climate station; the curves can be used as IDF curves for the City of Waterloo and the City of Kitchener. The Pearson Type III (PE3) distribution was identified as the preferred distribution function for the data and formed the basis for estimating the quantiles required to form the IDF curves. The rainfall intensity values for the new IDF curves tend to be lower than the corresponding values for the existing curves for rainfall durations of up to one to two hours and generally slightly higher than the rainfall intensity values for the existing curves for the longer rainfall durations. The results indicate that the existing IDF curves for the City of Waterloo and the City of Kitchener are likely somewhat conservative for rainfall durations less than two hours, although the impacts of climate change could result in more severe events in the future."

The University of Waterloo findings are consistent with the 'general lack of detectable trend signal' in past rainfall observations as reported by Environment and Climate Change Canada (ECCC). ECCC reported even some regional decreasing trends (St. Lawrence region of southern Quebec and the Atlantic Provinces) for the short duration intensities affecting urban drainage systems:

Trends in Canadian Short‐Duration Extreme Rainfall: Including an Intensity–Duration–Frequency Perspective Mark W. Shephard, Eva Mekis, Robert J. Morris, Yang Feng, Xuebin Zhang, Karen Kilcup & show all Pages 398-417, Published online: 19 Nov 2014 (Atmosphere-Ocean).

What do the University of Waterloo findings look like? These intensity-duration curves for 5-year, 25-year and 100-year rain frequencies show that for duration less than 2 hours, the storm severity has been decreasing:

IDF update climate change Kitchener Waterloo 5 year
IDF update to assess climate change impacts for sewer design shows decreasing 5-year rainfall intensities for durations less than 120 minutes (2 hours) - small flashy urban drainage systems now have lower extreme rainfall risk than with previously higher rainfall. Therefore earlier designs using older, higher rainfall design intensities have a safety factors against extreme weather risks for frequent events, and climate change has not adversely affected Kitchener-Waterloo erosion risks or erosion damage potential (erosion risks are often governed by frequent storm stresses). 

IDF update climate change Kitchener Waterloo 25 year
IDF update to assess climate change impacts for sewer design shows decreasing 25-year rainfall intensities for durations less than 90 minutes (one and a half hours) - small flashy urban drainage systems subject to nuisance flooding now have lower extreme rainfall risks. Therefore earlier storm drainage designs using older, higher rainfall design intensities, have a safety factors against extreme weather risks, and climate change has not adversely affected Kitchener-Waterloo flood risks or damage potential. Wastewater systems that have extraneous flow stresses (i.e., inflow and infiltration) and that respond to short duration rainfall appear to have lower capacity stresses with climate change IDF update. A Class Environmental Assessment Master Plan study in Kitchener has shown that peak wastewater flows in the trunk systems (e.g., Ottawa, Manchester, Montgomery trunks) are most highly correlated to short duration rainfall intensities. A Class Environmental Assessment study of the Sandrock Greenway trunk has also shown that smaller local wastewater systems respond to short duration rainfall intensities, even without high inflow potential in catchments with fully and partially-separated foundation service catchments).

IDF update climate change Kitchener Waterloo 100 year
IDF update to assess climate change impacts for sewer design shows decreasing 100-year rainfall intensities for durations less than 90 minutes (one and a half hours) - small flashy urban drainage systems now have lower extreme rainfall risk today compared to previously higher intensities. Therefore earlier designs using older, higher rainfall design intensities have a safety factors against extreme weather risks for rare storm events, and climate change has not adversely affected flood risks or flood damage potential. 

 Why do derived IDF values decrease? Because the observed maximum rainfall amounts in the Annual Maximum Series (AMS) have been decreasing. The following two graphs show trends in annual maximum rainfall recordings from 1971 to 2007. The 5-minute duration maximum rainfall has been decreasing and the 2-hour maximum rainfall have been flat - it is over this range that IDF intensities have been shown to be decreasing n the earlier graphs.






***
Comparing University of Waterloo analysis with politician statements:

Prime Minister Justin Trudeau recently stated "We are a government grounded in science". If so, why has he stated that 100 year storms may occur every 10 years or sooner following 2017 flooding in Gatineau? There is no data to support the storm frequency statement made by the Prime Minister.

Comparing University of Waterloo analysis with insurance industry statements:

The insurance industry, interested in flood damages and the effect on business activities, has stated that storms that happened every 40 years are now occurring every 6 years. Environment and Climate Change Canada has clearly refuted this frequency shift, most recently in Canadian Underwriter saying its studies do not support the insurance industry statement. As noted in the recent article:

"Associate Editor’s Note: In the 2012 report Telling the Weather Story, commissioned to the Institute for Catastrophic Loss Reduction by the Insurance Bureau of Canada, Professor Gordon McBean writes: “Weather events that used to happen once every 40 years are now happening once every six years in some regions in the country.” A footnote cites “Environment Canada: Intensity-Duration-Frequency Tables and Graphs.” However, a spokesperson for Environment and Climate Change Canada told Canadian Underwriter that ECCC’s studies “have not shown evidence to support” this statement."

The following detailed review of insurance industry statement and comparison with Environment and Climate Change Canada's Engineering Climate Datasets clearly shows how the insurance industry has confused projected rainfall intensity shifts with trends from past observations: