Less Extreme Ontario Rainfall - Precipitation Intensities For Design of Buried Municipal Stormwater Systems by Yi Wang. A Thesis presented to The University of Guelph

Those with decreasing rainfall intensities
could be Singing in the Rain, with lower
stresses on their buried municipal
infrastructure systems.

Wang's Ph.D. thesis at the University of Guelph describes changes in frequent and extreme rainfall trends. The thesis is available here. Confidence limits on 2-year, 5-year, 10-year and 25-year rainfall intensities for durations of 5 minutes to 2 hours show no significant changes in most cases and decreasing rainfall intensities at many stations.

Results from page 51 show that there are more than twice as many decreases in rainfall as increases considering the 90% confidence limit, as shown below:



Table 3.2: Results of 90% Confidence Interval Comparison Test

ID     5min 10min 15min 30min 1h  2h
6034075 ---- ---- ---- ---- ---- ----   Kenora A
6037775 ---- ---- ---- ---- ---- ---   Sioux Lookout A
6057592 ---- ---- ---- ---- ---- ----   Sault Ste Marie A
6085700 ---- ---- ---- ---- ---- ----   North Bay A
6100971 ---- ---- ---- ---- ---- ----   Brockville PCC
6104175 ---- ---- ---- ---- ---- ----   Kingston Pumping Station
6105978 ---- ---- ---- ---- ---- ----   Ottawa CDA RCS
6116132 ---- ---- ---- ---- ---- ----   Owen Sound MOE
6131415 ---- ---- ---- --↓↓ --↓↓ ----   Chatham WPCP
6131983  /    /   ---- -↑↑↑ --- ----   Delhi CS
6136606 ---- ---- ---- ---- ---- ----   Port Colborne
6137362 -↓↓↓ ---- ---- ---- ---- ----   St Thomas WPCP
6139525 ↓↓↓↓  /   ↓↓↓↓ ↓↓-- --- ----   Windsor A
6142400 ---- ---- ---- ---- ---- ----   Fergus Shand Dam
6144478 ---- ---- ---- ---- ---- ----   London CS
6148105 ---- ---- ---- ---- ---- ----   Stratford MOE
6150689 ---- --- ↑↑-- ---- ↑↑-- ---   Belleville
6153301  /   ---- ---- ---- ---- ----   Hamilton RBG CS
6158355 -↓↓↓ -↓↓↓ ---- ---- ---- ----   Toronto City
6158733  /   ----  /    /    /    /     Toronto Intl A
6158875 ---- ---- ---- ---- ---- ----   Trenton A

·        The arrows and hyphens in cells represent the results of CI comparison of 2, 5, 10, and 25-year events (from left to right). An up-arrow indicates an increase of rainfall intensity occurred in the 2nd period of record, and a down-arrow  indicates a decrease of rainfall intensity. A hyphen means no significant change (α = 0.1) is shown or, in other words, the CIs are not significantly different. Cells with slashes represent records that are not stationary.

11 significant increases , 24 significant decreases
Southwestern to Central Ontario most significant decreases

Results from page 52 show that there are almost twice as many decreases as increases considering the 80% confidence limit, as shown below:

Table 3.3: Results of 80% Confidence Interval Comparison Test

ID    5min 10min 15min 30min 1h  2h
6034075 ---- ---- ---- ---- ---- ----   Kenora A
6037775 ---- ---- ---- ---- --- ↑↑--   Sioux Lookout A
6057592 --- ---- ---- ---- ---- ----   Sault Ste Marie A
6085700 ---- ---- ---- ---- ---- ----   North Bay A
6100971 ---- ---- ---- ---- ---- ----   Brockville PCC
6104175 ---- ---- ---- ---- ---- ----   Kingston Pumping Station
6105978 ---- ---- ---- --- --- ----   Ottawa CDA RCS
6116132 ---- ---- ---- ---- ---- ----   Owen Sound MOE
6131415 ---- ---- ---- -↓↓↓ --↓↓ ----   Chatham WPCP  
6131983  /   ---- --- -↑↑↑ -↑↑↑ ----   Delhi CS
6136606 ---- ---- ---- ---- ---- ----   Port Colborne 
6137362 -↓↓↓ --- ---- ---- ---- ----   St Thomas WPCP
6139525 ↓↓↓↓  /   ↓↓↓↓ ↓↓↓↓ --- ---   Windsor A
6142400 ---- ---- ---- ---- ---- ----   Fergus Shand Dam    
6144478 ---- ---- ---- --- ---- ----   London CS
6148105 ---- ---- ---- ---- ---- ----   Stratford MOE
6150689 ↑↑-- ↑↑-- ↑↑↑- --- ↑↑—  ↑↑↑↑   Belleville    
6153301  /    /   ---- --- -↓↓↓ ----   Hamilton RBG CS
6158355 ↓↓↓↓ -↓↓↓ -↓↓↓ ---- ---- ----   Toronto City
6158733  /   ----  /    /    /    /     Toronto Intl A
6158875 ---- ---- ---- ---- ---- ----   Trenton A

·        The arrows and hyphens in cells represent the results of CI comparison of 2, 5, 10, and 25-year events (from left to right). An up-arrow indicates an increase of rainfall intensity occurred in the 2nd period of record, and a down-arrow  indicates a decrease of rainfall intensity. A hyphen means no significant change (α = 0.1) is shown or, in other words, the CIs are not significantly different. Cells with slashes represent records that are not stationary.


24 significant increases , 41 significant decreases
Southwestern to Central Ontario most significant decreases

***

Ontario climate change extreme rainfallHere are Wang's tables in original graphic format:


Ontario climate change rainfall

Climate-driven variability in the occurrence of major floods across North America and Europe - Journal of Hydrology Review

An assessment of major flood trends was conducted by a group of researchers including Environment and Climate Change Canada and University of Waterloo Civil and Environmental Engineering. They found no evidence that climate change has to date increased the occurrence of floods.

"Abstract:
Concern over the potential impact of anthropogenic climate change on flooding has led to a proliferation of studies examining past flood trends. Many studies have analysed annual-maximum flow trends but few have quantified changes in major (25–100 year return period) floods, i.e. those that have the greatest societal impacts. Existing major-flood studies used a limited number of very large catchments affected to varying degrees by alterations such as reservoirs and urbanisation. In the current study, trends in major-flood occurrence from 1961 to 2010 and from 1931 to 2010 were assessed using a very large dataset (>1200 gauges) of diverse catchments from North America and Europe; only minimally altered catchments were used, to focus on climate-driven changes rather than changes due to catchment alterations. Trend testing of major floods was based on counting the number of exceedances of a given flood threshold within a group of gauges. Evidence for significant trends varied between groups of gauges that were defined by catchment size, location, climate, flood threshold and period of record, indicating that generalizations about flood trends across large domains or a diversity of catchment types are ungrounded. Overall, the number of significant trends in major-flood occurrence across North America and Europe was approximately the number expected due to chance alone. Changes over time in the occurrence of major floods were dominated by multidecadal variability rather than by long-term trends. There were more than three times as many significant relationships between major-flood occurrence and the Atlantic Multidecadal Oscillation than significant long-term trends."

The paper is available from the Journal of Hydrology. The authors are from across the world.

Glenn A.HodgkinsaPaul H.WhitfieldbDonald H.BurncJamieHannaforddBenjaminRenardeKerstinStahlfAnne K.FleiggHenrikMadsenhLuisMedieroiJohannaKorhonenjConorMurphykDonnaWilsong
a
U.S. Geological Survey, 196 Whitten Road, Augusta, ME 04330, United States
b
Environment and Climate Change Canada, 401 Burrard Street, Vancouver, BC V6C 3S5, Canada
c
University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
d
Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Wallingford, Oxfordshire OX10 8BB, United Kingdom
e
Irstea Lyon, Hydrology-Hydraulics, 5 rue de la Doua BP32108, 69616 Villeurbanne cedex, France
f
Albert-Ludwigs-Universität Freiburg, Fahnenbergplatz, 79098 Freiburg, Germany
g
Norwegian Water Resources and Energy Directorate, P.O. Box 5091, Majorstua, 0301 Oslo, Norway
h
DHI, Agern Allé 5, DK-2970 Hørsholm, Denmark
i
Technical University of Madrid, ETSI Caminos, Canales y Puertos, c/ Profesor Aranguren, 3 28040 Madrid, Spain
j
Finnish Environment Institute, SYKE, Freshwater Centre, P.O. Box 140, 00251 Helsinki, Finland
k
Irish Climate Analysis and Research UnitS (ICARUS), Department of Geography, Maynooth University, Maynooth, Co. Kildare, Ireland

Since rainfall intensities are not increasing dramatically across Canada, as demonstrated by Environment and Climate Change Canada (ECCC) in the Atmosphere-Ocean in 2014, saying rainfall intensities are stationary, it makes sense that major floods are not increasing either. Of course there may be local regional trends - ECCC found that there are decreasing rainfall intensities in regions such as the St Lawrence basin of southern Quebec and the Maritimes. Their Engineering Climate Datasets (version 2.3) also show twice as many statistically significant decreasing trends as increasing ones in southern Ontario.

The paper Climate-driven variability in the occurrence of major floods across North America and Europe focused on minimally altered catchments in order to isolate climatic as opposed to hydrologic drivers. It focused on large watersheds. As noted on this blog, urbanization is a key driver of flood risk in small urban catchments and is expected to have increased of the past  50-100 years in many Ontario cities. This is link to GIS mapping of changes: Ontario city urbanization affecting runoff and flood risk since from 1966 to 2000.

If Hurricane Harvey hits Toronto will it be "The Day After Tomorrow" Stormageddon, Rainpocalypse? Sensational pseudo-science in media should be viewed with caution.

hurricane harvey torontoThe comment below is awaiting moderation on The Weather Network. It is in response to the article "Visualizing what Harvey's impacts would look like in Canada".

****

Toronto overland flooding NewtonbrookThe Weather Network broadcasts a segment on the movie The Day After Tomorrow calling it a silly, non-scientific tale and discounting the sensational stormageddons portrayed in the movie. This article is just similar sensationalization, and I caution even calling it 'pseudo-science' because there are too many gaps in basic hydraulics and hydrology to make the weather-flood math even worth dissecting. A couple cool graphics, but no science in the article. An alternative? Yes, it is possible to analyze the impact of storms on cities using urban hydrology and hydraulics to estimate where water could spread - I have assessed Toronto for the 100-year storm spread and multiples of that spread that could represent how a mega-storm could affect the city, street by street: 
Toronto urban flooding overland flow May 2000 August 2005 July 2013 flood report
http://www.cityfloodmap.com/2017/01/city-of-toronto-overland-flow-map-100.html 
Toronto urban flooding Beaches East York Leaside
The interactive map at the link above can be used to explore your street's risk in Toronto (realistic storms, not sensational 'stormageddons'. I have done similar analysis for southern Ontario that uses complete elevation models of Ontario, considers rainfall statistics, applies hydrologic runoff principles and hydraulic flow principles: 

http://www.cityfloodmap.com/2016/06/ontario-overland-flood-risk-mapping.html 

A few 2D maps on hot spots and 3D renderings are attached. 

The Weather Network promotes Science Behind the Weather all the time but does not get into much depth on hydrology and hydraulics and other scientific disciplines that come into play between weather and flooding. 

***

And a follow-up comment:

Just checking the "math" on Toronto Hurricane Harvey flooding simulation. I give it an "A" in grade 9 Algebra - yes, 56.8 cubic kilometres of water will have a height of 90 metres over Toronto's 630 square kilometers - kudos for being able to divide a volume by an area to get a depth - that would just about immerse the 130 metre tall Royal York Hotel as shown. But a D minus in Geography - grade 9 kids learn about the water cycle and that rain runoff water flows off land - it does not stack up like jello unsupported from its sides like the Hurricane Harvey Toronto flood math suggests. A F in physics because runoff water is viscous and flows instead of ponding up vertically. E minus in hydrology for anyone with an engineering college technologist certificate - again, water accumulates over and runs off through watersheds not defined by municipal boundaries - the rainfall volume should actually be bigger than 56.8 cu.km because the Toronto watersheds extend beyond the political boundaries. D minus for hydraulics as when it rains runoff flows away based on the hydraulics and at times the storage routing of the urban drainage and river and lake systems. This means runoff does not stack vertically, some infiltrates into the ground for small storms, and most flows away during the storm with the flood depth determined by the hydraulics at the time of peak outflow. All 2nd year civil engineers know from basic hydrology courses that axiom. But in the Hurricane Harvey simulation it is not even a remote consideration, nor is basic watershed science and hydrologic cycle considerations. I really do encourage The Weather Network to focus on the science behind flooding and it requires a more broad perspective on scientific disciplines beyond meteorology. 

***

Below is a critique of the science of The Day After Tomorrow on Wikipedia. The Hurricane Harvey Toronto flooding simulation is also an impossible joke as well - a cheap thrill ride for the weak minded: 

Some scientists criticized the film's scientific aspects. Paleoclimatologist and professor of earth and planetary science at Harvard University Daniel P. Schrag said, "On the one hand, I'm glad that there's a big-budget movie about something as critical as climate change. On the other, I'm concerned that people will see these over-the-top effects and think the whole thing is a joke ... We are indeed experimenting with the Earth in a way that hasn't been done for millions of years. But you're not going to see another ice age – at least not like that." J. Marshall Shepherd, a research meteorologist at the NASA Goddard Space Flight Center, expressed a similar sentiment: "I'm heartened that there's a movie addressing real climate issues. But as for the science of the movie, I'd give it a D minus or an F. And I'd be concerned if the movie was made to advance a political agenda." According to University of Victoria climatologist Andrew Weaver, "It's The Towering Inferno of climate science movies, but I'm not losing any sleep over a new ice age, because it's impossible."


Patrick J. Michaels, a former research professor of environmental science at the University of Virginia who rejects the scientific consensus on global warming, called the film "propaganda" in a USA Today editorial: "As a scientist, I bristle when lies dressed up as 'science' are used to influence political discourse."College instructor and retired NASA Office of Inspector General senior special agent Joseph Gutheinz called The Day After Tomorrow "a cheap thrill ride, which many weak-minded people will jump on and stay on for the rest of their lives" in a Space Daily editorial.

Southern Ontario IDF Trends at Climate Stations with Long Term Records - Climate Change Impacts on Extreme Rainfall Severity

There is perpetual contradictory information on extreme rainfall frequency trends in the media. The prevailing statement is that weather is more extreme due to climate change and underlying global warming that increases the atmosphere's water vapour and capacity and to rain. A previous post has shown that the relationship between temperature, water vapour and extreme rainfall does not 'hold water' - that is a high temperatures, researchers at MIT and Columbia have not observed higher rainfall intensities as predicted by theory.

What about observed rainfall intensities and the extreme value statistics derived from them? This posts takes a deep dive into southern Ontario 100-year rainfall intensity trends in southern Ontario, focusing on Environment and Climate Change Canada's long term climate station records. The finding is that there is no prevailing increase in extreme rainfall intensities in southern Ontario and that generalized safety factors in design (say 20% buffer) can accommodate the effect of recent extreme events.

Some background information and notes:

Ontario climate change
Southern Ontario Annual Maximum Series Trends
i) Environment and Climate Change Canada (ECCC) reports trends in raw observed rainfall extremes - these annual maximum series (AMS) trends and their statistical significance were reviewed in a previous post. In brief, in southern Ontario there were more than twice as many statistically significant decreasing trends in raw observed extremes as increases, as shown in the table to the right.

Canada climate change severe storms extreme rainfall trends
Canadian Long Term Climate Station Annual Maximum
Recorded Rainfall Trends
ii) ECCC derives IDF statistics from the raw data and updates IDF curves and IDF tables from time to time. These statistics characterize the average and extreme intensities that engineers and design professionals can consider in sizing new infrastructure or remediating old infrastructure. The 100-year rainfall intensities (100 year "return period") are those we can expect with a 1-in-100 or 1% chance per year - this post reviews those extreme trends for short and long durations, but only stations with more than 45 years of record are used since its good practice to not estimate statistics too far beyond the record length. So the 7 Ontario stations in the table at right are reviewed - out of all the 5 minute to 24 hour trends in the table, these southern Ontario stations have increasing trends in only 30% of the maximum rainfall observations.

iii) The raw data and derived IDF data are called the "Engineering Climate Datasets". Five versions of this data were reviewed (pre v1 data up to 1990 obtained from ECCC archives, v1 data up to 2003, v2.2 data up to 2007 and v2.3 data up to 2013). This data is available on ECCC's ftp site with the exception of the pre v1 archives. The ftp link to Intensity-Duration-Frequency (IDF) Files is ftp://ftp.tor.ec.gc.ca/Pub/Engineering_Climate_Dataset/IDF/

iv) The Canadian Standards Association published PLUS 4013 (2nd ed. pub. 2012) - Technical guide: Development, interpretation and use of rainfall intensity-duration-frequency (IDF) information: Guideline for Canadian water resources practitioners  which indicates how extreme events could be considered in IDF curve updates and frequency assessment of those events. The guide notes "If an observation of the event is available from an IDF location, update the IDF calculations using the event and all subsequent years since the most recent update (not including intervening or subsequent years will bias the calculation)". The data below does not always meet this requirement to include subsequent years and so some statistics are noted to be potentially biased (i.e., statistics shifted by a large recent event).

v) To look back at pre-pre-version 1 rainfall intensities, statistical analysis of annual maximum data up to 1980 was completed assuming a log-normal distribution to estimate the 100 year statistics prior to and including 1980.

Short Duration 100-Year Rainfall Intensity Trends in Southern Ontario - 5 Minutes to 1 Hour

The following two charts show the 5 minute and 1 hour duration trends in IDF curve data from pre-version 1 to version 2.3 Engineering Climate Datasets. Only the Toronto International Airport (Pearson Airport in Mississauga, Ontario) has data updated in version 2.3 including 2013. These charts represent the rainfall intensities that govern urban infrastructure design - some large trunk sanitary sewer systems may be governed by longer duration volumes and intensities but most storm drainage systems will be most sensitive to short duration rainfall given the quick response time and flashiness of urban catchments (i.e., short catchment 'time of concentration' means the short duration IDF intensities govern).

IDF curve update Ontario short duration extreme rainfall 100 year 5 minute five minute
5 Minute 100 Year Rainfall Intensity Trends - IDF Curve Updates in Environment and Climate Change Canada's Engineering Climate Datasets for Southern Ontario Long Term Climate Stations (Windsor, St. Thomas, London, Mississauga (Toronto International Airport / Pearson), Toronto, Kingston, and Ottawa). 

IDF curve update Ontario short duration extreme rainfall 100 year 1 hour one hour
1 Hour Minute 100 Year Rainfall Intensity Trends - IDF Curve Updates in Environment and Climate Change Canada's Engineering Climate Datasets for Southern Ontario Long Term Climate Stations (Windsor, St. Thomas, London, Mississauga (Toronto International Airport / Pearson), Toronto, Kingston, and Ottawa). 
The short duration trends show overall decreasing 100-year 5 minute rainfall intensities for most stations. It is noted that the Kingston Pumping Station and Ottawa CDA climate stations have decades of continuously missing data and sporadic data in the early to mid 1900's. The July 8, 2013 storm in Mississauga/west Toronto increased the 5-minute intensity slightly, and increased the 1 hour 100 year intensity back up to pre-1980 levels. It is questionable whether the 2013 storm should be included in the IDF update based on the CSA guide approach. Including it can bias the record however it does not increase IDF curve values above earliest statistics so it could be maintained considering that it would not affect design standards based on earlier rainfall statistics for short durations.

The 1 hour duration 100 year IDF trends are mixed, with more decreases than increases progressing from 1980 to 1990. After 1990, there are more decreases than increases as well.

This suggests that drainage design standards based on earlier raw maximum rainfall observations (AMS's) and derived extreme rainfall IDF statistics, particularly short duration rare, 100-year intensities, are conservative considering today's climate, as defined by the most recent AMS and IDF curve data in the Engineering Climate Datasets.

Since drainage design incorporates safety factors, just like any other infrastructure, an allowance of 20% higher intensity to 'stress test' system performance could be considered in southern Ontario systems to account for future climate change uncertainty or the effect of significant events, even if they are considered statistical 'outliers' in the CSA IDF guide approach.

Since IDF curve data is only one input to hydrologic analysis and hydraulic infrastructure design, safety factors and resiliency in other design aspects could be considered before applying any IDF safety factor, especially where there are significant capital or lifecycle cost implications - e.g., are runoff coefficients conservative, accounting for intensification post-design, are conservative hyetographs used in simulations, are inlet control devices used to mitigate the effect of higher IDF curve intensities on storm sewer systems, is there adequate freeboard on major overland drainage systems to accommodate higher rainfall, etc.?

Moderate to Long Duration 100-Year Rainfall Intensity Trends in Southern Ontario - 6 to 24 Hours

IDF curve 100 year rainfall intensity trends for longer duration of 6 to 24 hours are summarized in the two charts below.

The 6 hour intensities show a consistent increase from 1980 to 1990 and mixed trends from 1990 to 2007. Statistics can be affected by single events (Mississauga/Toronto Intl A in 2014, or Ottawa CDA in 2004).

Generally, if a 20% safety factor is available, most systems could accommodate even the higher intensities that consider single extreme 'outlier' events - for example, Toronto and GTA or GTHA standards based on 1990 data, say 13.4 mm/hr at Toronto City (Bloor Street station ID 6158350) or 15 mm/hr at Toronto Intl A (Pearson Airport station ID 6158733) plus 20% would yield 16-18 mm/hr extreme weather 'stress test' intensities. Such values would be above the July 8, 2013 influenced 100 year intensity, meaning systems designed with the 20% design buffer would be resilient for design intensities considering larger storms as well. In Ottawa, adding 20% to the 1990 6 hour 100 year intensity of 13 mm/hr (station ID 6105976) would give a 15.6 mm/hr 'stress test' intensity which is also above the 2007 updated IDF intensity that considers the significant September 9, 2004 storm. Ottawa, in fact, already considers such as 20% design stress test - see slide 28 in this presentation.

IDF curve update Ontario extreme rainfall 100 year 6 hour six hour
6 Hour 100 Year Rainfall Intensity Trends - IDF Curve Updates in Environment and Climate Change Canada's Engineering Climate Datasets for Southern Ontario Long Term Climate Stations (Windsor, St. Thomas, London, Mississauga (Toronto International Airport / Pearson), Toronto, Kingston, and Ottawa).

IDF curve update Ontario extreme rainfall 100 year 24 hour daily total
24 Hour (Daily Total) 100 Year Rainfall Intensity Trends - IDF Curve Updates in Environment and Climate Change Canada's Engineering Climate Datasets for Southern Ontario Long Term Climate Stations (Windsor, St. Thomas, London, Mississauga (Toronto International Airport / Pearson), Toronto, Kingston, and Ottawa). 
The 24 hour IDF curve trends in southern Ontario are similar to the 6 hour trends with increases from 1980 to 1990 and a mix of decreases and increases since 1990. Increases occur when recent extreme events are factored in (2013 in Toronto and 2004 in Ottawa). Again, a 20% buffer on 1990 IDF intensities would generally cover the increase due to extreme 'outlier' events. Infrastructure systems that are sensitive to storage volume over long durations such as stormwater detention ponds could be reviewed based on the 20% stress test, not necessarily to alter design, but to test system performance in terms of surcharge risk in the upstream collection system, freeboard on spillway / overflow features, or cumulative changes to downstream floodplain limits (if the system is governed by return period storm as opposed to regional storm hurricane events, etc.).

Conclusion

With regular media reports echoing The Day After Tomorrow storm-apocalypse predictions when there are high lake levels that are not significantly above historical extremes, and Al Gore's Inconvenient Sequel providing alternative facts on hurricane frequency that, up until Hurricane Harvey, have been clearly decreasing in number of landfalls and GDP-normalized damages, there is a need to dig below the headlines, take advantage of Open Data and check if data really supports the headlines. Prime Minister Trudeau recently declared in Gatineau that we will have 100 year storms every few years, which data from Environment and Climate Change Canada (ECCC) does not support. ECCC routinely correct insurance industry statements on extreme weather trends like in this Canadian Underwriter article where IBC claimed storms were more frequent and ECCC issued this correction:

"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 IDF trend analysis above for southern Ontario long term climate stations supports the ECCC statement that there is no support for insurance industry claims - there is certainly no 40 year to six year frequency shift in 100 year rainfall intensities. A similar ECCC correction was made on Windsor area trends in a CBC News article, where an insurance broker stated "we're getting 20 times more storms now than we were 20 years ago.", and in response to a complaint (mine) CBC checked with ECCCcorrected the article adding "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."

Looking at the official data from 1990 and scaled to zero to put changes in perspective, the ups and down do not look dramatic overall. Below are those 5 minute, 1 hour, 6 hour and 24 hour 100 year IDF trends. It suggests we should "Keep calm and carry on"... especially if you have a 20% design buffer.

IDF curve update Ontario short duration extreme rainfall 100 year 5 minute environment canada climate adaptation

IDF curve update Ontario short duration extreme rainfall 100 year 1 hour 60 minute climate adaptation

IDF curve update Ontario extreme rainfall 100 year 6 hour six hour climate adaptation

IDF curve update Ontario extreme rainfall 100 year 24 hour daily precipitation climate adaptation

So some regions in Canada may have overall increasing trends in extreme rainfall (see second table of long term Canadian AMS trends), but southern Ontario does not appear to be one of them based on IDF data trends. This suggests that infrastructure that is designed or upgraded to 1990 IDF standards (i.e., pre ECCC version 1 Engineering Climate Datasets obtained from archives for this post's review) is largely resilient to today's climate, as there has been little change. Sensitivity to future, predicted IDF changes would be the next step in creating resilient infrastructure - it may be that upgrades to meet even the 1990 IDF 'weather' with a nominal safety factor will result in adequate climate adaptation co-benefits, depending on the resiliency in other hydrology and hydraulic analysis and design.