Practical Climate Change Resilience for the Stormwater Management and Wastewater Engineering Professional

Accounting for future climate change impacts is recommended in Ontario policies and regulations. A review of these drivers was described in a recent presentation as follows:

How are stormwater management and wastewater engineering professionals accounting for these impacts practically to meet the requirements of the Provincial Policy Statement, the Infrastructure Jobs and Prosperity Act, Environmental Assessment requirements and Planning Act amendments in Bill 139?  They are taking a couple of simple approaches: i) adjusting intensity-duration-frequency (IDF) curves to account for potentially higher future rainfall intensities, or stress testing systems with such higher intensities, or ii) stress testing systems with conservative hyetographs, i.e., rainfall patterns, in hydrologic and hydraulic simulation models.

Some examples are as follows:

1) City of Markham, Ontario - Wastewater Collection System

Markham evaluated the resilience of its wastewater collection system considering historical storms with a climate change adjustment (adding 30% to rainfall intensities) and its Chicago storm.  The Chicago storm hyetograph was determined to me more conservative than the adjusted historical storms and was deemed to account for future climate change effects as well as other uncertainties.  Results were presented at the WEAO 2018 annual conference.

2) City of Markham, Ontario - Stormwater System

Markham evaluated the resilience of a flood-prone stormwater collection system considering local IDF data, and its 3-hour AES design hyetograph. The 3-hour AES design storm intensities were above local IDF intensities, and the local and regional trends in intensities were found to be decreasing. The use of the 3-hour AES hyetograph was determined to be sufficient to account for future climate change impacts, as discussed in the 2019 Don Mills Channel Class EA study report.

3) Windsor/Essex Region, Ontario Stormwater Systems

Stantec developed the Windsor/Essex Region Stormwater Management Standards Manual in 2018. The manual includes a review of IDF trends and concludes "design standards should continue to rely upon the long-standing historical data provided by the Windsor Airport station" and that a “stress test” event, a 150 mm rainfall event be applied to assess vulnerabilities and any design adjustments to mitigate unacceptable risk - for new development unacceptable risk would include water levels above lowest building openings on a site. Therefore, IDF values have not been increased in design, but a practical stress test is applied to assess risks and adaptation requirements.

4) City of Ottawa, Ontario Storm Sewers and Stormwater Management Designs

Ottawa reviewed its IDF data in 2015 and found increases and decreases in IDF intensities at different durations and "that the percentage differences in intensities between the IDF curves is within the margin of error associated with data collection and hydrologic assessments, it was ISD’s opinion not to update the OSD IDF curves." A check storm is considered based on climate change research: "The 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. For these events, there is no requirement for a free board between the footing elevation and the hydraulic grade line elevation."

5) City of Moncton, and Town of Riverview, New Brunswick Major Stormwater System

These municipalities have incorporated a “20% allowance in the historical data of 1 in 100
year storm-major stormwater system” (Mohammed, 2016).

6) City of London, Ontario Subwatershed Studies

In 2011, based on University of Western future climate projections, the City of London resolved to  "increasing the City's existing Intensity Duration Frequency (IDF) Curves by 21% and that Civic Administration BE DIRECTED to incorporate this change in a phased approach starting with the subwatershed studies outlined below and ultimately adjusting other design standards, planning and Official Plan considerations in dialogue with interest parties".

7) Ministry of Transportation, Ontario Highway Drainage

The Ontario Ministry of Transportation (MTO) has comprehensively assessed future climate risks to highway drainage infrastructure including storm sewers, culverts and bridges (see 2015 document The Resilience of Ontario Highway Drainage Infrastructure to Climate Change). It found predicted decreases in short duration rain intensities:

"Predicted storms with durations less than 6 hours are less intense than those observed in 2007, for all return periods. Longer duration storms do not always hold to this pattern, with the 6 and 24 hour storms often predicted to become more intense, particularly in Northwestern Ontario. The magnitude of the difference in rainfall precipitation between the IDF curves, which are based on historical data and those developed from climate models, can be quite significant."

It also found in bias-corrected future climate models both predicted increases and decreases: "In some areas rainfall intensity increased from 0% to just above 30% where in other areas there were rainfall intensity reductions in the from 2 to 10%."

The impacts of a 30% increase in flow rates was found to have limited affect on highway drainage infrastructure:

"Based on the analysis of samples of highway infrastructure components there is demonstrated resilience of MTO drainage infrastructure to rainfall increases as a result of predicted climate change scenarios. An overwhelming percentage of the storms sewer networks tested appeared to have sufficient excess capacity to hand the increases in design flow rates up to 30%. Similarly, the sample of highway culverts analysed showed adequate capacities, for a large percentage of the culvert, to handle the rage of low rate increases investigated without the need to be replaced. The bridges tested also appeared to suffer no risk to structures as a result of the flow increases."

MTO issued a policy on how to consider future climate effects called Implementation of the Ministry’s Climate Change Consideration in the Design of Highway Drainage Infrastructure that indicates designers are to use the IDF Curve Lookup tool and then to consider future IDF values in sizing infrastructure:

"Designers are to exercise engineering judgement to determine whether the infrastructure will meet current and future design criteria through appropriate sizing of the infrastructure or through providing allowances for future adaptation measures."

However, it is noted that MTO does not necessarily adopt the future IDF curve for design and accepts "providing allowances" to adapt to those conditions in the future. This adaptation approach is consistent with the American Society of Civil Engineers' recommended Observational Method approach to managing uncertain future climate risks (see previous post).

Is Wild Weather and a New Normal for Severe Rainfall Responsible for Urban Flooding, or Urbanization and Hydrologic Stresses? Case Law Points to Urbanization Driving Runoff and Flood Effects.

Everyone has an opinion on the weather and media is saturated with stories linking extreme weather with flooding. It makes sense. Flooding happens during severe storms. The bigger the storm the bigger the flood damages in fact.

But media and groups including the insurance industry and some researchers have suggested that flooding and flood losses have increased due to changes in weather patterns characterized by increased intensity or frequency of rainfall events.

That is not true. And there is no data to support that explanation.

Why?

Because rainfall intensities have not changed according to official Engineering Climate Datasets that review and analyze trends in extreme rainfall to inform engineering design across Canada.

Some media are correcting this false explanation that new wild weather, or a new normal, is causing flooding, like the CBC.

The CBC Ombudsman has ruled that CBC News reporting violated standards of journalistic practice in reporting more 100 Year storms linked to urban flooding - see the scathing report. It begins:

"Review by the Office of the Ombudsman, French Services, CBC/RadioCanada of two complaints asserting that the articles by journalist Marc Montgomery entitled How to mitigate the effects of flood damage from climate change and Response to a climate change story, posted on September 19 and November 19, 2018, respectively by Radio Canada international (RCI), failed to comply with the CBC/Radio-Canada Journalistic Standards and Practices regarding accuracy and impartiality."

and regarding this claim in the article on changing storm patterns:

“We are experiencing storms of greater magnitude, more volume of rain coming down over short periods of time these days due to climate change. That is causing massive flooding.”

the CBC Ombudsman concludes that (my bold):

"One only had to examine the official Environment Canada data for Ontario as well as for the

entire country to acknowledge that the claim made in the article was inaccurate. Such

acknowledgement would at the same time have addressed the complainant’s criticism regarding

the lack of data to corroborate Dr. Feltmate’s claim about the increased frequency of extreme

rainfall events in Canada."

While Environment and Climate Change Canada have refuted insurance industry claims on storm frequency shifts in the past (see Canadian Underwriter correction on the IBC/ICLR Telling the Weather Story theoretical shifts mistakenly reported as real data).

Yet the insurance industry has continued to promote the 'causation', with opinion pieces (not any peer-reviewed paper or analysis) saying climate-change effects on rainfall drive flood losses. See Financial Post piece. 

If not rainfall, what causes more flooding, more flood damages?

Canadian courts have pointed to urbanization as a driver, as in the landmark case of Scarborough Golf Country Club Ltd v City of Scarborough et al.. The decision indicates that urbanization markedly increases runoff stresses that cause runoff, erosion and flooding. Some highlights:

i) "Expert evidence confirmed the effect of the city's rapid urbanization and water control plans on the creek." 

ii) "It is important to note that the case is not presented primarily as a complaint against flooding but rather that the markedly increased flows and increased velocity of flow have caused and continue to cause damage to the creek bed and the adjacent tableland.", and 

iii) "There can be no doubt that the storm sewer facilities and urbanization of the lands to the north of the Club are the cause of the effects just described and that the difference in flow and velocity of flow is very substantial." 

So urbanization markedly increases runoff, flows and velocities, while there are no observed changes in extreme rainfall. Mapping clearly shows the significant expansion of urban areas in southern Ontario municipalities - see post and images below:

The IPCC has reviewed the size and frequency of floods at larger regional scales in their extreme events report and noted limited to medium information to assess changes, also noting the effects of changes in land use and engineering (see page 8):

"There is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scales because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes."

IPCC notes low confidence in the sign of changes at a global scale, meaning flood magnitudes could be going up or down.

Other factors driving losses? Research shows for some severe weather event types like hurricanes the driver is GDP growth, e.g., "research is robust in concluding that, for many decades into the future, the primary driver behind increasing economic losses related to hurricanes is expected to be societal growth"  

More factors? Maintenance of infrastructure affects its performance and flood risks. For example, TRCA described that flooding of the Keating Channel and lower Don River, which affects Toronto's Don Valley Parkway was due to a lack of maintenance:

"Since its construction between 1914 and 1922, the Keating Channel has been subject to heavy sediment loads, requiring regular dredging to maintain sufficient depths to allow for and maintain shipping activities at the mouth of the Don River. Between 1950 and 1970, widespread development throughout the Don Watershed and the construction of the Don Valley Parkway increased sedimentation rates by up to four times that of the pre-was era. After 1970, decreases in the number of new watershed disturbances and improved sediment control structures likely contributed to the decline in sedimentation in the Keating Channel to levels similar to the pre-war era. A reduction in shipping activities within the Keating Channel, combined with restrictions on the open water disposal of dredgate imposed by the International Joint Commission (IJC) in 1974, resulted in a cessation of dredging in the Keating Channel. In the following five to six years, the Keating channel filled with sediment and debris to the point where it became visible under all but high lake levels, resulting in increased flood risk along the lower Don."

So flood risks increase due to fluviogeomorphology (the transport and deposition of sediments in a watercourse) and hydraulics - when dredging stops, sediment builds up, hydraulic capacity is reduced and flooding is increased along the river. 

Yet despite flooding dating back to the 1800's, as reported in the Inquiry for Premier Davis, and despite impacts on rail lines in the Don River floodplain over decades, flooding has been attributed to climate change effects. Even by the Environmental Commissioner of Ontario. The fact is there is no new normal with "wild weather", but the same old issues and extremes:

Hydraulics affect sewer system capacity and flood risks as well. Modifications to store sewage and prevent discharge to the environment can constrain capacity and contribute to higher back-up risks, as documented in approved Class Environmental Assessment Studies in Ontario. Call this "The Law of Conservation of Poop" - holding back sewage in the collection system to prevent overflows causes surcharge levels to rise, sometimes closer to basements, increasing basement flooding risks. The excerpt below from the Toronto Area 32 Municipal Class EA describes "Causes of Flooding" related to operation of the tanks installed to protect Lake Ontario and beach water quality:

And while stormwater runoff and sewage level are rising in storm and wastewater collection systems due to urbanization and hydraulic constraints, risks are being increased by lowering basements, exposing higher value finishing and contents to flood damages - in Toronto, the rate of basement lowering, tracked through Toronto Open Data building permits for foundation underpinning, has increased significantly as shown in this post. The chart below shows the data trends:

A new report "Canada’s Changing Climate Report" lead by Environment and Climate Change Canada confirms that there is no change in extreme rainfall in Canada based on observations (see Chapter 4) saying "There do not appear to be detectable trends ...":

This certainly contradicts claims made by an insurance industry-funded research group that have indicated there is 'a lot of data to show it' when it comes to bigger storms. A February, 8, 2018 presentation to the Standing Senate Committee on Energy, the Environment and Natural Resources included this statement:

"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."

But a review in a recent presentation to the National Research Council's 2018 workshop on flooding that showed there is no data to support the statement. Concerns with insurance industry statements on frequency shifts were also expressed by Environment and Climate Change Canada staff in relation to the Telling the Weather Story 40 year to 6 year weather shift. Staff had concerns with statements that could confuse theory and actual changes. Here is an excerpt from communications regarding the Telling the Weather Story normal bell curve theory shift:

"The presentation looks to be a simple conceptual model for communicating the underlying idea – if one assumes a standard normal, then a shift in the mean implies an attendant change in extremes – which is fine as far as it goes. If this is used as the basis for statements about actual changes in extreme rainfall in Canada, then I would have concerns."

Here was the specific question posed:

Here is a graphic showing the theoretical shift in question, an arbitrary 1 standard deviation shift in a standard normal 'bell curve' (probability density function):

The Environment and Climate Change Canada report also speaks to theoretical shifts in probability density functions, like the Weather Story bell curve shift. This is the example showing a shift right in the distribution of extreme events Figure 4.2.1:

The reality is that in some regions when it comes to extreme rain intensities there is not a shift to the right but a shift to the left, meaning less extreme events, as shown in this annotated curve that reflects southern Ontario rain intensity shifts:

The 'green' shift to the left reflects an overall decrease of 0.4% in rainfall design intensities at 21 long term climate stations since 1990, considering durations related to urban flooding, i.e., 5 minutes to 24 hours. That analysis of the new Version 3.0 Engineering Climate Datasets was presented in this post.

There is often a statement that changes in means will lead to changes in extremes in a distribution of probabilities - this makes sense. This concept is reflected in IPCC reports as well:

But data shows that the means, the 2 Year storm rain intensities, the events that we have the most observations of and the most confidence in assessing trends are decreasing the most. The Version 3.0 datsets review for southern Ontario shows on average a drop of -0.8% in those rain intensities, as shown on this table in the first column:

In this region, the extremes can be expected to decrease along with the means - on average that is happening too for the 100 Year rain intensities.

The Environment and Climate Change Canada report notes 'medium confidence' in increases in annual precipitation across the country and "low confidence in quantifying regional or national total amounts of precipitation" - so medium confidence in it going up but low confidence in saying how much, especially at more local spatial scales, or regions.

Since little or no infrastructure is designed to address annual precipitation, the reports limitations on the annual precipitation statistic are irrelevant to cities facing challenges like urban flooding during extreme, short duration events. Based on CatIQ datasets, a higher number of flood claims and a higher value of claim is associated with rare storm volumes falling over duration of minutes and hours and not annual totals.

The key take-away is that extreme rainfall has not been observed to change, whether for higher frequency events like 2 Year storms, or for low frequency, rare events, like 100 Year storms.

It is easy for the media to confuse annual precipitation with rain extremes, and in the case of Canada’s Changing Climate Report, CBC News reported that urban flooding related to intense rain will increase too - CBC has since corrected that article noting the report did not find increased short-duration rainfall linked to basement flooding:

The Environment and Climate Change Canada report cites research that points to land use change having a "key role" in affecting flooding, for example for the southeast Prairies flood in 2014. Here is the excerpt on attribution of flooding to rainfall or other factors, saying "Anthropogenic influence may have influenced rainfall, but landscape modification played a key role in increased runoff":

This is consistent with reporting by the American Society of Civil Engineers who in their Adapting Infrastructure and Civil Engineering Practice to a Changing Climate document state: "It is important to point out that land-use changes (e.g., urbanization) can result in substantial flooding impacts, independent of climatic forcing functions." - see page 12.

Regarding attribution, it is also consistent with a recent report on extreme rainfall event attribution that also identifies a lack of association of extreme convective storms, those responsible for much urban flooding, with anthropogenic climate change effects. For example the National Academies of Sciences, Engineering, and Medicine. 2016 report Attribution of Extreme Weather Events in the Context of Climate Change states (see page 97):

"Studies of trends in the United States find different results depending on the time period and spatial region chosen, but there is no broad agreement on the detection of long-term trends in overall severe
convective storm activity such as might be related to anthropogenic climate change."

Regarding land use influence on runoff and flood risk, this is also consistent with analysis by the University of Guelph's Engineering Department on changes in urban 'runoff coefficients' (the fraction of rain that runs off and can contribute to flood stresses) due to urbanization like in the Don River watershed:

That analysis was intended to 'disentagle' the impacts of climate change and land use change. Green bars are pre-urbanization coefficients showing we had a small fraction of rain becoming runoff, while blue bars show significant increase in runoff potential after 50% urbanaization. Note there is uncertainty in flow monitoring too, just like in precipitation monitoring, but we see a 10 times, 1000% increase in runoff potential in summer months, when we have the highest rain intensities, due to urbanization. The urbanization effects are MASSIVE - the Scarborough Golf court case reiterated this fact over and over referring to "markedly increased flows".

Compared to urbanization effects on flows, meteorologic effects are a big "nothing burger", with no observed changes and just a lot of theory and speculation. We should design for uncertainty in the future, and incorporate cost-effective adaptation considerations or flexibility for future adaptation (ASCE's Observational Method for climate adaptation) however we should not mischaractierize past trends and risk factors driving today's infrastructure performance limitations.

The University of Guelph analysis also indicates that spring peak flow rates will decrease with climate change effects that reduce winter snowpacks and spring melt flood potential. The follow chart shows the decrease in spring peaks in the rural Moira River watershed:

The Environment and Climate Change Canada report recognizes the impacts of temperature on snow patterns in Chapter 4: "As temperatures increase, there will continue to be a shift from snow to rain in the spring and fall seasons.". The report also cites research that "The reduction in spring snow pack and the ensuing reduction in summer streamflow in British Columbia have been attributed to anthropogenic climate change". Other cited research notes "Such a change in the form of precipitation, from snow to rain, has profound impacts in other components of the physical environment, such as river flow, with the spring freshet becoming significantly earlier." - the University of Guelph research shows that the winter period flows increase from November to early March in the Moira River example, and the peaks decrease significantly from late March and April. This decrease in peaks will result in a decrease in spring flood risks in watershed affected by such events.

So there is no new wild weather, or new normal driving flood damages. Case law in Ontario defining the effects of hydrology, or urbanization, findings of inquiries into Don River flooding for Premier Davis, Municipal Class Environmental Assessment studies investigating basement flooding causes and solutions, and Environment and Climate Change Canada's Engineering Climate Datasets that examine trends in observed rainfall intensities show us that hydrology, hydraulics, fluviogeomorphology explain today's flood risks, and there is has been no shift in rainfall intensities, despite median and insurance industry 'weather stories' and claims.

Environment Canada Report Confirms No Overall Change in Extreme Rainfall - Generally Random Ups and Downs - Stated Certainty of Future Shifts Contradicts American Society of Civil Engineer's "Significant Uncertainty"

A new Environment and Climate Change Canada (ECCC) report Canada’s Changing Climate Report https://changingclimate.ca/CCCR2019/ reviews past, observed rainfall extremes https://changingclimate.ca/CCCR2019/chapter/4-0/ and confirms there are no observed changes in extreme rainfall across the country:

"For Canada as a whole, there is a lack of observational evidence of changes in daily and short-duration extreme precipitation."

ECCC predicts increases showing a theoretical probability density function shift (Figure 4.21) where the blue line probability density function represents today's/yesterday's eventt magnitudes and frequencies without climate effects, and red represents with effects (shift right means higher magnitude for any frequency):

Engineering Climate Datasets in some regions show trends in the magnitude of rain intensity magnitudes (reality) going the other way however:
https://www.cityfloodmap.com/2019/03/idf-updates-for-southern-ontario-show.html .

This image shows the difference between the theory and the local data reality - the green line is the REALITY showing for any given frequency (2, 10, 50, 100 Year events) the magnitude is going down in southern Ontario:

ECCC suggests there is insufficient data to observe the changes in extremes expected: "Estimating changes in short-duration extreme precipitation at a point location is complex because of the lack of observations in many places and the discontinuous nature of precipitation at small scales." - while that MAY be accurate for extreme events that are rare and elusive, why do 2 Year rain intensities, derived from many, many yearly observations at all long term rain gauges, show the clearest decline, across all durations from 5 minutes to 24 hours?

Surely, we have DO enough point locations and observations to see the change in these small storms. But if these small frequent storm intensities are no higher with today's temperature shifts, why do we expect the extremes to be higher either? Data we do have shows in southern Ontario these 100 year intensities are 0.2% LOWER on average. So extremes are shifting shifting along with the means.... shifting lower.

A theoretical probability density function shift has been promoted in the past by ICLR and IBC in the 2012 Telling the Weather Story report:

This has been shown to be 'made-up' and not related to real data (ECCC IDF tables and charts mistakenly cited as the source of the 40 year to 6 year frequency shift) - this chart shows the theoretical 1 standard deviation shift widely circulated by IBC and real data shifts:

See the difference between theory and data? It is pretty clear.

Given the lack of past trends, and uncertainty in future noted in the ECCC report ("It is likely that extreme precipitation will increase in Canada in the future, although the magnitude of the increase is much more uncertain"), we must follow the American Society of Civil Engineer's recommended "Observational Method" approach see 2015 report Adapting Infrastructure and Civil Engineering Practice to a Changing Climate at http://theicnet.org/wp-content/uploads/2015/07/2015-07-ASCE-Practice-to-Climate-Change-2015.pdf, and also see https://ascelibrary.org/doi/book/10.1061/9780784415191?utm_campaign=PUB-20181023-COPRI%20Alert&utm_medium=email&utm_source=Eloqua# for the new 2018 manual on engineering practice Climate-Resilient Infrastructure, Adaptive Design and Risk Management.

The ASCE 2018 manual promotes incorporating any no-regret, now cost measures in design today considering most probable future conditions, and allowing design flexibility to adapt in the future if and when performance is shown to be inadequate or affected by future changes - this is a practical approach intended to avoid costly over-design, and over-investment in potentially unnecessary and cost-ineffective infrastructure today.

While the ASCE 2015 report notes the high degree of uncertainty "However, even though the scientific community agrees that climate is changing, there is significant uncertainty about the location, timing and magnitude of the changes over the lifetime of infrastructure."

In contrast, the ECCC report appears to asset a high degree of confidence in future changes saying "For Canada as a whole, there is a lack of observational evidence of changes in daily and short-duration extreme precipitation. This is not unexpected, as extreme precipitation response to anthropogenic climate change during the historical period would have been small relative to its natural variability, and as such, difficult to detect. However, in the future, daily extreme precipitation is projected to increase (high confidence). - how can ECCC assert high confidence when there are no observed trends? How can ECCC contradict ASCE's statement on high "signifcant uncertainty'?

ECCC reports that summer precipitation is expected to decrease: "Summer precipitation is projected to decrease over southern Canada under a high emission scenario toward the end of the 21st century, but only small changes are projected under a low emission scenario." - how can that be if the summer temperatures are going up? Does this not violate the Clausius-Clapeyron theory cited in the ECCC report states that "increased atmospheric water vapour in this part of the world should translate into more precipitation, according to our understanding of physical processes" - so that is a theory - what about the real data? What does it show? the Clausius-Clapeyron relationship does not stand up to scrutiny as shown in a previous post.

Given highest rainfall extreme are in the summer (see the work of Dr. Trevor Dickinson on seasonal extremes), a summer decrease in precipitation could potentially mean lower flood risks. The data for southern Ontario already show a decrease in the annual maximum series (reflecting lower means and typical 2 Year design intensities in derived IDF curves) and the extreme 100 Year design intensities are decreasing slightly as well.

Overall, many in the media have over-hyped concerns about changing rainfall severity. Data and ECCC's report shows there has been no change, beyond random fluctuation. Looking ahead the American Society of Civil Engineers indicates that future changes have "significant uncertainty"- this contracts the ECCC's statement on "high confidence" on future extremes.

IDF Updates for Southern Ontario Show Continuing Decrease in Extreme Rainfall Intensities Since 1990 - Environment and Climate Change Canada's Engineering Climate Datasets Version 3.0

The Annual Maximum Series (AMS) charts in a recent post show updated trends in observed maximum rainfall volumes over various durations. Design rainfall intensities, equivalent to volumes over the various durations, are derived by fitting a statistical distribution to the observations, resulting in intensity-duration -frequency (IDF) values presented in tables and charts for each climate station. A previous post examined trends in IDF values for long-term record stations in southern Ontario based on 1990 to version 2.3 values (updated to 2001 to 2013 data) - see link - the overall decrease in intensities was 0.2 percent with more frequent, small return period, values decreasing the most.

The extended, updated version of Environment and Climate Change Canada's Engineering Climate Datasets has IDF values based on data up to 2017 and was released in March 2019. Information is available from the Environment and Climate Change Canada's ftp site through this link on their website.

Again we can compare design intensity values from 1990 with the current, updated values and determine if older design standard values are appropriate and conservatively above today's values or if updates to standards are required to reflect more intense rainfall rates. For this review, 8 of the 21 stations have had updates to IDF values since the version 2.3 datasets. The average length of record increased from 42 to over 46 years, averaged across all stations and statistics. The charts below show the average change in intensity for all durations grouped together (top chart Figure 1) and considering variations across durations (bottom chart Figure 2).

Figure 1 - Average Change in Southern Ontario IDF Values for Engineering Design by Return Period - Record-Length Weighted Changes Between 1990 and Version 3.0 Datasets for 21 Climate Stations with Long Term Records

Figure 2 - Average Change in Southern Ontario IDF Values for Engineering Design by Duration and Return Period - Record-Length Weighted Changes Between 1990 and Version 3.0 Datasets for 21 Climate Stations with Long Term Records

 Observations are that:

●     Rainfall intensities are decreasing even further than in the last review.

●     The changes in IDF values based on more recent observations are very small and reflect only minor random ups and downs - changes in IDF values due to assumed statistical distribution selection are greater than observed rain data changes. No “new normal” or “wild weather” due to a changing climate.

●     Frequent storm intensities (those used for most storm sewer design) are decreasing for all durations.

●     The more frequent the storm the greater the decrease in design intensity.

●     Rainfall intensities are decreasing more for short durations than longer ones (see short duration red and orange bars in Figure 2).

●     Less frequent, severe storm intensities (25 year to 100 year return periods) are deceasing on average.

●     Severe storm intensities are decreasing most for short durations.

The following tables summarize values in the above charts. Note that the chart data is weighted by record length so that longer trends are given proportionately more weight. The tables show both weighted and unweighted values -giving more weight to longer record stations results in a greater overall decrease in IDF rainfall intensity statistics.

Table 1 - Trend in Southern Ontario Intensity Duration Frequency Values for 21 Long-Term Climate Stations, Weighted by Record Length - 0.4 Percent Average Decrease in Intensities 

Table 2 - Trend in Southern Ontario Intensity Duration Frequency Values for 21 Long-Term Climate Stations, Not-weighted by Record Length - 0.2 Percent Average Decrease in Intensities

What does this mean for engineering design? In general, older design IDF values or curves are conservative reflecting older, higher observed rainfall intensities. Infrastructure designed to older standards will be slightly more resilient today, having a marginally greater safety factor and higher performance under today's extreme weather conditions. Older infrastructure may be stressed by hydrologic or hydraulic factors, or intrinsically lower design standards - see previous posts here on hydrologic factors including at many southern Ontario cities in this post. How the updated values affect municipal engineering design is shown below on an annotated Table 1.

Table 1 Annotated - What has changed? What are IDF values used for? What does this mean for municipal infrastructure engineering design and resilience of sewer and pond designs?

The implications for municipal infrastructure design based on governing durations and frequencies are annotated around the first table. This shows that:

●     storm sewers, designed to convey high frequency, short duration intensities, are facing lower rainfall intensities since 1990;

●     major drainage systems designed for low frequency longer durations (because critical conveyance segments are often lower in the system where times of concentration are longer) are facing no change in design rainfall intensity;

●     storm water ponds designed to hold low frequency, high return period, long duration storms are facing no change in design rainfall volumes.

This just reflects historical trends in southern Ontario, so how about future changes under climate change that should be considered in design? After all, Bill 138’s Planning Act amendments and O.Reg.588/17 require municipalities to identify how they will accommodate climate change effects in infrastructure policies and plans.

The American Society of Civil Engineers ASCE has created a guide that can be considered and that classifies infrastructure by it's criticality, based on potential loss of life and economic impact as well as the service life of the asset to determine an approach for addressing potential future climate change effects. The guide is "Climate-Resilient Infrastructure: Adaptive Design and Risk Management". One of the principles is that given uncertainty with future climate, one may design with today's climate if the risk class is low, as long as future adaptation is feasible. The guide also promotes an approach called the Observational Method (OM), defined as follows:

"The Observational Method [in ground engineering] is a continuous, managed, integrated, process of design, construction control, monitoring and review that enables previously defined modifications to be incorporated during or after construction as appropriate.All these aspects have to be demonstrably robust. The objective is to achieve greater overall economy without compromising safety."

The OM approach has been adapted by ASCE to designing climate resilient infrastructure and has the following steps:

1. Design is based on the most-probable weather or climate condition(s), not the most unfavorable and the most-credible unfavorable deviations from the most-probable conditions are identified.

2. Actions or design modifications are determined in advance for every foreseeable unfavorable weather or climate deviation from the most-probable ones.

3. The project performance is observed over time using preselected variables and the project response to observed changes is assessed.

4. Design and construction modifications (previously identified) can be implemented in response to observed changes to account for changes in risk.

For new subdivisions, adaptation/modifications noted in the last steps could be implemented in the future if rainfall intensities increase. Some relatively minor local system modifications representing adaptation activities could include:

●     adding or modifying storm inlets with control devices to limit capture into the storm sewer (upstream of where future HGL risks are predicted);

●     adding plugs to sanitary manhole covers to limit inflows (where significant overland flow spread and depth is predicted);

●     modifying the outlet of stormwater ponds to optimize storage for larger storms (e.g., add intermediate-stage relief components to limit over control);

●     increasing the capacity of overflow spillways in stormwater ponds to convey larger storms that cannot be stored (e.g., widen or line with erosion protection to a higher stage);

●     increase pond storage capacity through grading of side slopes (e.g., steeper slopes or steps/walls) at time of sediment removal/cleaning (NB - slope material may be used to bulk up high moisture content sediment to accelerate cleaning schedule);

●     sump pump disconnection of gravity drained foundation drains (weeping tiles) for lowest, at risk basements where insufficient freeboard exists to future higher HGL.

In addition, property owners in any areas of increased risk could be made aware of those and be encouraged to raise insurance coverage limits or consider lot-level flood proofing as well. The benefits of the ASCE's stated OM approach is that it can accommodate future climate change effects without over-designing or over-investing in today’s infrastructure. This is feasible if future adaptation opportunities exist in today's design and if new subdivisions have a relatively high level of resilience already (i.e., safety factors, freeboard values, redundancy, conservative design parameters) such that future changes do not drop effective performance in most areas across a system into a realm where damages will occur. There may be risks in critical sections of the infrastructure system that where designed to the limits of current standards.

Considering an OM approach for southern Ontario climate resilience we are in an observation stage (Step 3) now, having skipped Step 1 and designed most systems for historical IDF characteristics, and not having considered adaptation measures in advance (Step 2). Given that rainfall intensities have not changed, the project performance will not have changed since the system was originally designed with historical IDF values. Therefore no modifications/adaptations are required to account for rainfall trends. It is unlikely that performance variation in a new subdivision could be confidently determined for decades given that the chances of experiencing an event that tests design performance are low. Any performance monitoring may have the co-benefit of informing the baseline performance under historical design standards, as explicit consideration of safety factors is not common, and it is possible that modern systems are exceeding their intended capacity and performance level due to these intrinsic design safety factors. 

For retrofitting older infrastructure systems, the IDF data is not as critical in determining risk as is the selection of a design hyetograph that will use this data. Most older systems have level of service gaps for yesterday’s and today's climate and extreme weather, leading to current flood risks.

Looking at the OM approach for retrofitted systems, the noted changes in southern Ontario IDF values since 1990 will have no bearing on performance and flood risks and would not trigger project modifications/adaptation. Some conservative design hyetographs used in retrofit analysis do incorporate a safety factor that could account for future climate effects as well as other hydrologic (e.g. antecedent conditions) or operational uncertainties (e.g. local blockages, clogged grates). For example, some municipalities use a Chicago storm distribution that is conservative in terms of system response - this was examined in detail in this WEAO 2018 Conference Paper and presentation. That type of conservative design hyetograph pattern could limit the project response to future IDF changes experienced under less extreme real storm patterns.

What is more uncertain perhaps, at that requires observations, is the baseline performance of the retrofitted system and how well it mitigates flood risk given the diverse range of failure mechanisms possible. That is, infrastructure upgrades on the public collection system will not alleviate lot-level risks that remain, resulting in baseline performance gaps regardless of changes in IDF values or baseline system design. This should be an area of future research, i.e., to quantify baseline mitigation effectiveness (i.e., performance) - as many factors affect performance and occur together at the same time, it may be difficult to separate out what performance variations are due to weather variations versus other factors. For example, real storms have a significant spatial and temporal variability compared to simplified design assumptions (typically spatially and temporally uniform rainfall) - this was explored at a recent National Research Council workshop on urban flooding (see slides 17-19 for a recent example of real-world temporal and spatial variability compared to design assumptions).  Nonetheless, an observed gap in performance regardless of the cause can trigger adaptation/modifications to restore performance of a project to its intended level of service. This would likely be possible only if performance is significantly below expectations.

***

Other related posts and links:

1. CBC Ombudsman's scathing ruling on journalistic standard violation regarding extreme rainfall reporting - link,
2. CBC Radio Canada interview on the importance of data and gaps in media reporting - link,
3. Financial Post OpEd on insurance industry claims correlating flood losses to extreme weather trends - link,
4. Water Environment Association of Ontario (WEAO) Influents magazine article on flood risk drivers - link,
5. National Research Council national workshop presentation on extreme rainfall trends (this inspired the southern Ontario IDF review in this and earlier posts) - link,
6. WEAO OWWA joint climate change committee presentation on flood risk factors including IDF trends and hydrologic factors - link,
7. Review of “Telling the Weather Story” report citing theoretical IDF shifts as real Environment and Climate Change Canada data - link,
8. “Thinking Fast and Slow on Floods and Flow” exploring heuristic biases in framing and solving problems surrounding extreme rainfall and flood risks - link.

Premier snubs Ontario Society of Professional Engineers with form letter - OPSE says "missed the intent"

So sad for Ontario. Premier sends a form letter in response to OPSE letter on climate and energy policy and the Ontario Action Plan on Climate Change.

..... it goes on but it does not acknowledge the substance of the OPSE letter. So OPSE has sent another letter to Premier Wynne:

... it goes on. The kicker is this closing statement:

"OPSE wants a response from you that acknowledges the importance of engineering expertise and commits to consulting with OPSE and Ontario's engineers, now and in the future."

OPSE suggests the Premier missed the intent of the communications, but it is likely that the Premier just does not care.

As Joe Oliver writes in the Financial Post

"Ontario Premier Kathleen Wynne is behaving like an environmental activist unburdened by accountability, rather than a government leader devoted to protecting the welfare of her constituents."

Obviously the Premier believes that the engineering profession would be a burden and bring unnecessary accountability to Ontario's environmental and energy sectors.