Woodbine
1
MECP Stormwater Design and Permissions Working Group
May 1, 2019
IDF Trend Analysis,
Future Climate Projections &
System Design for Extreme Weather
Resiliency
Robert J. Muir, M.A.Sc., P.Eng.
Manager, Stormwater, City of Markham

Woodbine
Outline
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• Policies on Infrastructure Climate Effect Assessment
• Environment and Climate Change Canada (ECCC) Engineering
Climate Datasets (Version 2.3 & Version 3.0)
– Annual Maximum Series Trends and Significance
– Regional IDF Trends Since 1990
• Future IDF Projections & Uncertainty
• Hyetograph Selection as Critical Risk Design Factor
• Future Resiliency Design Approaches in Ontario Municipalities

Provincial Policy Statement (2014):
“Infrastructure … shall be provided in a coordinated, efficient and cost-effective
manner that considers impacts from climate change ….”
Infrastructure for Jobs and Prosperity Act (2015):
“Infrastructure planning and investment should minimize the impact of infrastructure on the
environment … should be designed to be resilient to effects of climate change.”
Environmental Assessments (2017):
“… proponents to consider measures to adapt to climate change: How vulnerable might
a project be to a changing climate?
Bill 139 (2017) Planning Act Amendments:
“OP shall contain policies that identify goals, objectives and actions to … provide for
adaptation to a changing climate, including through increasing resiliency.”
Ontario Drivers for Assessing Climate Change Risks
3Provincial Policy Statement 2014 Infr. for Jobs and Prosperity Bill 139EAs and Class EAs

ECCC Annual Maximum Rainfall Trends
• ECCC introduced trend
analysis in the v2.3
Engineering Climate Dataset,
showing trend direction and
statistical significance at
each station:
http://climate.weather.gc.ca/prods_servs
/engineering_e.html
• Ottawa Airport
 Decrease 5-min to 6-hrs.
 Increase 12 to 24 hrs.
 Statistically significant
decrease over 10-min,
15-min, and 1-hr. 4

Very Few Significant Trends in Canada (random)
• 93% of trends are not
significant or ‘no data’.
• 5-min rainfall maxima
have significant increases
at 2.7% of stations.
• Decreasing regional
trends in southern QC
and Atlantic. Increasing
on coasts (SW BC and
NFLD).
5
Significantly
Down 3%
Significantly
Up 4%2.7%
http://www.cityfloodmap.com/2015/12/trends-in-canadian-shortduration.html

National Data Trends Contradict Marketing Claims
• Insurance ‘facts’ & infographics
on rain trends refuted by ECCC:
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Data facts from ECCC:
– “No Detectable Trend Signal” (Atmosphere-
Ocean, 2014)
– “ECCC studies have not shown evidence to
support statement” (Cdn Underwriter, 2016)
– Advertising Standards Canada complaint
resolutions 2015-2018 reject ads
– “If this is used as the basis for statements about
actual changes in extreme rainfall in Canada,
then I would have concerns.” (ECCC, 2018)
– “failed to comply with the CBC/Radio-Canada
Journalistic Standards and Practices regarding
accuracy and impartiality.” (CBC Ombudsman,
2019)
http://https://www.slideshare.net/RobertMuir3/storm-intensity-not-increasing-factual-review-of-engineering-datasets

ECO Material Contradicts ECCC Data
• ECO report makes statement on
storm frequency without citing data.
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http://https://www.cityfloodmap.com/2015/11/milli-vanilli-blame-it-on-rain.html
“now “1-in-100
year” storms,
which are often
the threshold for
resilient design,
are happening
more frequently”
(press release)
• ECO report repeats incorrect
“Weather Story” theory on rain
frequency shifts as fact.
“extreme storms of
a magnitude
expected to happen
every 40 years are
now predicted to
occur every six
years”

Ont Gov. Material Contradicts ECCC Data
• 2019 Budget on Addressing Climate
Change claims more frequent
extreme weather events.
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http://http://budget.ontario.ca/pdf/2019/2019-ontario-budget-en.pdf
“The effects of a
changing climate,
such as more
frequent extreme
weather events,
are already
underway.” (page
155)
• EBR 013-4992 posting claims more
extreme weather events .
“As more extreme weather events occur
that threaten our homes, businesses and
infrastructure … ”
http://http://www.ebr.gov.on.ca/ERS-WEB-
External/displaynoticecontent.do?noticeId=MTM3NjQ1&statusId=MjA5Nzgw&language=en

Mixing-up Annual Precipitation Data and Extreme Storm Risks
“Indeed in Canada, in southern Canada we are getting about 18% more
rainfall on an annual basis than was the case just over 100 years ago. So
when you see in the news and the media people talk about storms seem
bigger and more intense and so forth, those perceptions are correct. And
there's a lot of data to show it. I'm just giving one quick illustration here.”
Blair Feltmate, Intact Centre on Climate Adaptation, February, 8, 2018
Standing Senate Committee on Energy, the Environment and Natural Resources
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FOI Request Revealed No Data on Bigger Storms:
link: University of Waterloo letter March 27, 2018

Less Extreme Short Duration Rain - Southern Ontario
• 97 % of trends not statistically significant (mild trends up & down).
• 2.3% statistically significant decreases and only 1.0 % significant
increases in intensity. No short duration significant increases.
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97%
http://www.cityfloodmap.com/2016/02/ontario-climate-change-trends-going.html
V2.3 Datasets

Reports Have Some Selective Data, Not Overall Trends
• LID Manual (2nd draft) only cites increases omits decreases.
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https://drive.google.com/open?id=1NHtrjCglDgox4tYISLU5LLZYS32Ea4MN
See Table 6.1
“The St Lawrence region experienced negative trends
for all durations and significant trends were found for
the 5, 10 and 15 min storm durations. The South region
for the 5 and 10 min storms experienced significant
negative trends, and all trends in the South regions,
with the exception of the 2 h duration, were negative.”
https://drive.google.com/open?id=1m7WVAEY7tHhDolQzGekDZGW5m-m1h0Iq

Decrease in Maximum Annual Observed Rain in S. Ontario
• 21 stations with
47 years of data
(average) have
42% more
decreasing
maximum rain
trends than
increasing
trends.
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https://www.cityfloodmap.com/2019/03/environment-and-climate-change-canada.html
V3.0 Engineering Climate Datasets – 2019

More Decreases Than Increases Across All Durations
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https://www.cityfloodmap.com/2019/03/environment-and-climate-change-canada.html

Decrease in Derived IDF Values in S. Ontario
• Long term
stations have
decreasing IDF
design intensity
values since 1990:
– 5-Min -1.8 %
– 24-hr -0.1 %
– Overall -0.4 %
14https://www.cityfloodmap.com/2019/03/idf-updates-for-southern-ontario-show.html

Decreases Across 2 Year to 100 Year Design Intensities
• Long term
stations have
decreasing IDF
design intensity
values since
1990:
– 2 Yr -0.8 %
– 100 Yr -0.2 %
– Overall -0.4 %
15https://www.cityfloodmap.com/2019/03/idf-updates-for-southern-ontario-show.html

Short Duration (5 Minute) Decreases Greatest
• Intensities that
govern much
sewer design (< 1
hour durations)
have decreasing
IDF design values
since 1990.
16https://www.cityfloodmap.com/2019/03/idf-updates-for-southern-ontario-show.html

100-Year 15-Minute
Future IDF
Uncertainty
• Various options:
– Tool / Method
– Station / Cell
– RCP/ Conf.
Bands
– Timeframe
• Wide diversity in
future volume
across options.
• No consistency in
governing option
across durations.
IDF CC Tool
2050-2100
CCDP
2065-2095
RCPs RCPs RCPs RCPs 10-90% 10-90% 10-90%
Local Climate Stations Local Grid Cells
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100-Year 15-Minute
Future IDF
Uncertainty
• Various options:
– Tool / Method
– Station / Cell
– RCP/ Conf.
Bands
– Timeframe
• Wide diversity in
future volume
across options.
• No consistency in
governing option
across durations. 18
H
L

100-Year 2-Hour
Future IDF
Uncertainty
• Various options:
– Tool / Method
– Station / Cell
– RCP/ Conf.
Bands
– Timeframe
• Wide diversity in
future volume
across options.
• No consistency in
governing option
across durations. 19
H
L

100-Year 24-Hour
Future IDF
Uncertainty
• Various options:
– Tool / Method
– Station / Cell
– RCP/ Conf.
Bands
– Timeframe
• Wide diversity in
future volume
across options.
• No consistency in
governing option
across durations. 20
H
L

100-Year 24-Hour
Future IDF
Uncertainty
• Various options:
– Tool / Method
– Station / Cell
– RCP/ Conf.
Bands
– Timeframe
• Wide diversity in
future volume
across options.
• No consistency in
governing option
across durations. 21
H
L
Stantec - Windsor/Essex Region Stormwater Management Standards Manual, 2018
See Climate Change – Practical Guidance for the SWM Practitioner
See Appendix A for Review of Future IDF Methods
https://essexregionconservation.ca/wp-content/uploads/2018/12/WE-Region-SWM-Standards-Manual.pdf

Hyetograph Selection Significantly
Affects System Performance and
Resiliency
• IDF data are applied in practice to derive design
storm rainfall patterns within hydrologic simulations
to assess performance
• Chicago storm: “the synthetic storm pattern would
undoubtedly have a greater return period than the
IDF curve from which it was derived” (Marsalek
and Watt, 1984)
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Hyetograph Selection Effects Major Runoff Peaks (Storm)
• Various 100-year storms to assess peak flows in Toronto InfoWorks models.
• “Chicago” distribution gives higher overland, major system design flows:
• 108% higher in small catchment
• 60% higher in medium catchment
• 36% higher in large catchment
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Description
Minor Peak (m3/s) Major Peak (m3/s)
Chicago AES Chicago AES
Area 15 – Small Catchment 0.16 0.15 0.25 0.12
Area 15 – Large Catchment 3.74 3.66 0.45 0.33
Area 17 – Small Catchment 0.12 0.10 0.34 0.22
Area 17 – Medium Catchment 2.79 2.72 0.32 0.20
Area 17 – Medium Catchment 1.28 1.25 1.49 1.01
Area 17 – Large Catchment 49.09 48.37 0.07 0.05

Hyetograph Selection Effects Surcharge (Sanitary)
• Several wastewater design storms were used to assess surcharged manholes
representing basement flooding risks in Markham’s all-pipe InfoWorks model.
• “Chicago” storm has highest surcharge/flood potential (conservative):
– 20 times more flood risk compared to historically-based design storms.
– 4.3 times more flood risks compared to Region operational / trunk storm.
– Higher risk for Today’s IDF than other storms with Future IDF (stress tests
for Climate Change resiliency, demonstrates safety factors in design)
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Design Storm
# MH Flooded
(< 2m freeboard)
% MH Flooded
(< 2m freeboard)
York Region 25-Year 'Historical' 60 0.42 %
Toronto May 2000 'Historical' (25-50 Year) 51 0.35 %
Ottawa 100-Year 'Historical / Scaled' 13 0.09 %
Markham 100-Year Chicago 259 1.80 %

IDF Data Use (To Create Hyetograph) is Most Critical to Risk
• Regulatory floodplain hyetographs can underestimate 100-year rain by 90%.
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0
50
100
150
200
250
300
0 100 200 300 400 500
RainfallIntensity(mm/hr)
Time (minutes)
Markham Storm (3 Hr
AES) 100 Year
TRCA Storm (AES 12
Hr) 100 Year
Markham 100-Yr
IDF 100-Yr
TRCA 100-Yr
Markham 100-Yr
TRCA 100-Yr
Risk
Gap

Southern Ontario Extreme Rain Trends Decreasing
http://www.cityfloodmap.com/2017/11/less-extreme-short-duration-rainfall-in.html
http://www.cityfloodmap.com/2017/09/less-extreme-ontario-rainfall.html
http://guelph.ca/wp-content/uploads/SMMP-Appendix_E_Combined_IDF_Report.pdf
“new rainfall depths are lower
than current by 10 to 15 %”,
EarthTech
https://drive.google.com/open?id=1Gxmg8gtkzZuv-ZqiqYpc3tQ9r-Ie1v1p 26https://drive.google.com/open?id=1AngUYFFlm-RqQlmSC0gZqxy8nV61BW8J
15+ Studies Confirm No Appreciable Increase
https://www.cityfloodmap.com/2018/03/extreme-rainfall-and-climate-change-in.html

No Change in Past IDF, But Allowances for Future Changes
• Municipalities have reviewed IDF trends, design standards and
recommend practical design methods / tests for resiliency:
– Windsor/Essex Region, 2018 - “no evidence to increasing IDF curves for stormwater
conveyance design”, “long-standing historical rainfall data from Windsor Airport continue
to be used for design standards”.. recommends rural 24-Hr SCS Type II and urban
24-Hr Chicago “stress test” hyetographs
– Niagara Falls, 2015 - “Updated IDFs for four of the five climate stations within the City
were found to generate rainfall volumes and intensities that were slightly lower than
those generated by the previous IDF curves .. recommends “5% increase to provide
a safety factor in the design of future stormwater infrastructure (and upgrades) to
account for possible future climate change impacts”
27https://www.cityfloodmap.com/2018/03/extreme-rainfall-and-climate-change-in.html

No Change in Past IDF, But Allowances for Future Changes
• Municipalities have reviewed IDF trends, design standards and
recommend practical design methods / tests for resiliency:
– Welland, 2012 - “1963 curves were conservative relative to the current (2000)
estimates and even relative to the projected (2020 and 2050) values for many
duration/return interval combinations.” … recommends “it is reasonable to retain the
1963 intensities”
– Markham, 2018 - “100-year short-duration intensities are considered to be stationary
for the purpose of the existing system capacity assessment under today’s climate - past
rainfall intensities (IDF data) maybe used”.. recommends conservative Chicago
Storm hyetograph for wastewater systems & 3 hour AES design storm to provide
resiliency for both current and future rainfall extremes for storm systems
28https://www.cityfloodmap.com/2018/03/extreme-rainfall-and-climate-change-in.html

No Change in Past IDF, But Allowances for Future Changes
• Municipalities have reviewed IDF trends, design standards and
recommend practical design methods / tests for resiliency:
– Ottawa, 2015 - “2007 IDF Curves are less than the OSG [Ottawa Sewer Guidelines]
IDF Curves on average by 5% and 10% for the 5 year and 100 year curves
respectively..” … recommends “storm sewer system performance also has to be
checked for historical storms as well as a 20% increase in the 100 year rainfall
volume for climate change stress testing” but does not require HGL freeboard to
footing elevation
29https://www.cityfloodmap.com/2018/03/extreme-rainfall-and-climate-change-in.html

Conclusions
• ECCC Engineering Climate Datasets Version 3 trends & significance for
each station/duration define extreme rain intensity changes:
– Short duration intensities define urban flood risk and conveyance
system design requirements (not annual precip.)
– Local station and even regional trends may be up or down.
– Local IDF changes follow observed intensity trends (e.g., lower IDF
values in southern per Ontario ECCC datasets & countless studies).
• Media / marketing / reporting claims of increasing rainfall trends divert
focus from key flood risk drivers and resilience design priorities.
• Future IDF predictions highly variable – practical stress tests proposed by
some municipalities provide for future safety factors / resiliency.
• Hyetograph selection more critical to defining risk than IDF refinements -
(synthetic design storm proposed to assess future climate resiliency). 30