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IDF Trend Analysis, Future Climate Projections & System Design for Extreme Weather Resiliency

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Presentation on policies promoting climate resilience in Ontario, a review of insurance industry and government agency statements on extreme weather trends, a review of national and local engineering climate datasets annual maximum series and derived IDF trends, particularly southern Ontario. A review of engineering and academic studies for multiple municipalities highlights many unsupported claims on extreme weather trends. Practical design approaches given decreasing or stationary IDF trends, and allowances for future climate changes effects are noted, including the consideration of design stress test analysis with synthetic hyetographs or rain intensity increases. Design hyetographs are shown to be more critical to infrastructure system design than IDF curve shifts in regions such as Southern Ontario.

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IDF Trend Analysis, Future Climate Projections & System Design for Extreme Weather Resiliency

  1. 1. 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
  2. 2. Woodbine Outline 2 • 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
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. National Data Trends Contradict Marketing Claims • Insurance ‘facts’ & infographics on rain trends refuted by ECCC: 6 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
  7. 7. ECO Material Contradicts ECCC Data • ECO report makes statement on storm frequency without citing data. 7 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”
  8. 8. Ont Gov. Material Contradicts ECCC Data • 2019 Budget on Addressing Climate Change claims more frequent extreme weather events. 8 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
  9. 9. 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 9 FOI Request Revealed No Data on Bigger Storms: link: University of Waterloo letter March 27, 2018
  10. 10. 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. 10 97% http://www.cityfloodmap.com/2016/02/ontario-climate-change-trends-going.html V2.3 Datasets
  11. 11. Reports Have Some Selective Data, Not Overall Trends • LID Manual (2nd draft) only cites increases omits decreases. 11 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
  12. 12. 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. 12 https://www.cityfloodmap.com/2019/03/environment-and-climate-change-canada.html V3.0 Engineering Climate Datasets – 2019
  13. 13. More Decreases Than Increases Across All Durations 13 https://www.cityfloodmap.com/2019/03/environment-and-climate-change-canada.html
  14. 14. 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
  15. 15. 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
  16. 16. 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
  17. 17. 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 17
  18. 18. 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
  19. 19. 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
  20. 20. 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
  21. 21. 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
  22. 22. 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) 22
  23. 23. 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 23 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
  24. 24. 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) 24 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 %
  25. 25. IDF Data Use (To Create Hyetograph) is Most Critical to Risk • Regulatory floodplain hyetographs can underestimate 100-year rain by 90%. 25 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
  26. 26. 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
  27. 27. 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
  28. 28. 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
  29. 29. 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
  30. 30. 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

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