As Ontario develops its Environment Plan, how it build resilience to extreme weather and mitigate flood damages in our communities should be a key consideration. To do so, we will need to identify and pursue technically-effective and financially-sustainable approaches to reduce flood risks. The following post explores reporting on floods, examines risk factors driving flood losses, and discusses challenges and opportunities for risk mitigation solutions that policymakers can consider. Further analysis on the role of green and grey infrastructure, including benefit-cost analysis to help guide infrastructure investment priorities, will be presented at the Water Environment Association of Ontario annual conference in April 2019 (see paper).
R. Muir
Feb. 2, 2019
Flooding and Extreme Weather (Climate Change) in the Headlines
Flooding and concerns
with severe weather continue to dominate headlines especially when summer
storms impact Ontario municipalities, whether in Toronto in 2018, Windsor in
2017, Burlington in 2014, Toronto in 2013, Ottawa in 2009, Peterborough in 2004
or Stratford in 2002. Similarly, spring river flooding and high lake levels
like those across the Grand River watershed in 2018 or around Lake Ontario in
2017 are often accompanied by declarations of a ‘new normal’[i] of extreme conditions due
to more frequent or intense storms as a result of climate change. These recent
events are associated with high economic losses and, tragically, have even
resulted in loss of life[ii]. Therefore the need for
strategic infrastructure planning that addresses flood resiliency and addresses
these impacts in a timely and sustainable manner continues to be a priority for
Ontario municipalities and water management agencies.
Understanding the
engineering factors affecting flooding, sometimes misreported in the media, can
help explain risks and identify opportunities for ‘weathering the storms’ and
improving community resilience, including evaluating the role of emerging natural/green
technologies promoted in the media, and in some industry circles[iii], and now being
considered in Ontario water management policies.
What Causes Flooding?
The majority of
summer storm impacts affecting Ontario municipalities result from how cities
were built and how they have grown - that is, a combination of long-standing
limitations in historical infrastructure capacity and urbanization pressures
over many decades[iv].
Simply put, sewer pipes designed and installed fifty to one hundred years ago
were never sized to handle extreme weather conditions responsible for today’s
flooding, and were intended to accommodate lower amounts of development -
designing to effectively convey runoff overland following very heavy rain only
became a common practice in Ontario in the 1980’s. Similarly, flooding along
river valleys and around lakes results from the long-standing intrinsic risks
facing historical settlements due to their location relative to expected high
water levels - planning to effectively situate development above and beyond
these flood plains became common in only the 1950’s and later decades with the
continued advancement of flood hazard mapping and regulation.
In the media today,
infrastructure design limitations and urbanization stresses are sometimes
identified as factors contributing to flooding, but they seldom recognized as
the dominant factors to be managed - as a result there is a tendency to
speculate on changes in weather patterns as opposed to recognize the basic
physical limitations present under today’s or yesterday’s weather conditions.
Is Flooding Getting Worse?
Yes, in some cases. No,
in others. The frequency and severity of flood events along rivers may have
increased due to historical growth in watersheds that took place before modern
engineered runoff control practices. Urbanization can increase flood risk due
to higher runoff, flow rates and water levels and intensification in high risk
zones can increase exposure to these risks, making flood conditions and flood
impacts worse[v].
Such higher risks can occur across large watersheds as well as within local
neighbourhoods beyond river valleys and where historical development may have
buried small local creeks, limiting the capacity for rainwater to safety runoff
during extreme weather. It is commonly accepted that increases in flood risk
accompany growth in Gross Domestic Product (GDP) - Ontario’s GDP has increased
by 35% from 2000 to 2017[vi], suggesting the potential
for more at risk property. But in rural watersheds, unaffected by urbanization,
changes in winter temperatures have actually lowered spring flows and flood
risk, by increasing the amount of steady melt runoff throughout the winter
(i.e., due to dramatically more frost-free days)[vii].
Complicating the
situation, infrastructure systems may be constrained over time which can also
make localized flood impacts worse. Sometimes improvements made to
transportation systems, such as constructing underpasses to reduce traffic
disruptions and improve safety at historical at-grade railway crossings,
exposes resulting low lying roadways to more frequent flooding[viii]. Similarly, wastewater
collection system retrofits to enhance water quality protection, like the
installation of control tanks or the adjustment of regulator structures to
prevent wastewater overflows to waterways, can incrementally increase local
flood risks as wastewater is held back in the sewer system to protect the
environment[ix]. Infrastructure systems
are therefore complex and their design may involve trade-offs between competing
performance goals (e.g., flooding vs. environmental protection). In addition,
the capacity of sewer systems can be reduced by a range of other local factors,
such as inadvertent encroachment by utilities cross-bored through sewer pipes
or the build-up of calcite deposits or other debris between regular maintenance
cycles. While these factors can worsen flood risk by lowering infrastructure
capacity, the exposure of individual properties may increase at the same time
as well, aggravating flood damage potential. For example the practice of
lowering basements through foundation underpinning to enhance living spaces can
increase the risk of damage further just by shifting vulnerable property closer
to any high water or wastewater levels in city sewers[x].
There are some
dramatic examples of infrastructure failures that could suggest flood impacts
are getting worse, such as the wash-out of Finch Avenue West in Toronto during
the August 2005 storm[xi]. A review of historical
failures in the Toronto region, however, suggests a significant decrease in
these types of failures as the design and construction practices for roads and
bridges have improved - more resilient engineering practices are now resulting
in more limited instances of washouts and lower vulnerability compared to the
early and mid 1900’s[xii], despite an increasing
number of roadways and structures in our communities.
Sometimes dramatic
flooding events are deemed unprecedented in the media and the event may be
explained by more severe weather and climate change effects. Careful review of
data records may contradict such suggestions, for example in the case of the
stranded Toronto commuter train along the Don River in July 2013. While some
media reports suggested the event was unprecedented, records indicate that
higher flooding occurred weeks before the incident[xiii] and a comprehensive
inquiry in the 1980’s revealed long-standing railway risks dating back to the
1800’s. A review of media archives shows the Toronto commuter train was
stranded in the same location in 1981 as well[xiv].
Overall, some flood
impacts are getting worse, often due to a range of under-reported factors. Over
time historical infrastructure design limitations become apparent, sometimes
accentuated by urbanization over previous decades. Infrastructure failures,
including roadway and bridge wash-outs are fortunately extremely isolated
despite some dramatic examples. In some cases, dramatic flood events may
reflect limited operational practices to manage long-standing risks, as opposed
to any changes in intrinsic risk factors.
Are Storms Bigger and More Frequent Due To Climate Change?
Not necessarily.
While the number of flood events may appear to be on the rise due to
urbanization stresses and other considerations, bigger and more frequent storms
is not a key factor in many Ontario cities. In fact, numerous engineering
studies[xv] to review design
standards in the face of climate change concerns and the official Engineering
Climate Datasets have shown extreme rainfall trends across southern Ontario
have remained unchanged for decades[xvi]. This runs counter to
common media suggestions that link any flood trends directly to rainfall
trends, but often in the absence of any rainfall analysis or comprehensive
consideration of local runoff hydrology and infrastructure hydraulic factors.
In some regions, such
a northern Ontario, increases in rainfall intensity have been observed in
historical rainfall records. While many climate change models predict more
extreme rain intensities in the future in Ontario due to climate change, there
is a high degree of uncertainty, and some models predict decreasing extremes[xvii].
So based on
observations and statistical analysis, storms are not necessarily more severe,
despite recent media statements to the contrary that may even state there is a
definitive change in baseline conditions that affects every single extreme
weather event[xviii].
Notwithstanding the lack of clear historical trends, precautionary engineering
design must always consider safety factors to account for potential changes in
storm frequency or severity, and consider the natural unpredictability of
weather systems. There is a significant opportunity for professional engineers
and specialists to educate the media and non-technical stakeholders on severe
weather trends affecting flooding.
The recent call for
‘immediate action’ on climate change effects by executives from Intact
Financial and Sun Life[xix] shows that flood risk
factors are not well understood.
Are Water Levels Higher Today Due To Climate Change?
Not necessarily.
While 2017 Lake Ontario levels were certainly well above average levels, long
term records show that historical high levels were only barely exceeded by a
few centimetres in 2017[xx]. Occasionally breaking
records is something that should be expected to occur to some degree over any
long record period - consider that in the second year of any water level
recording that if the first year had average levels, there is a 50% chance of
‘breaking the record’ in the second year. Even where there are long term
observations like on the Great Lakes, records should be expected to be broken
and considered when planning land uses or designing vulnerable infrastructure.
Expanding
encroachment upon the lakeshore environment, whether from residential
development (e.g., Toronto Island), or the early spring use of beaches by
volleyball leagues (e.g., Woodbine Beach), can accentuate conflicts with high
water levels that are largely reflective of the ‘old normal’ and not higher
water levels due to a changing climate. In the media, it is common to report on
high water levels without a broad consideration of historical water level data
which can serve to mischaracterize the rarity of particular levels. Sometimes
the nature of community encroachment has changed more than the water levels,
making the impacts of high water levels more severe.
In some water
systems, operational considerations can affect water levels regardless of variability
in the climate and weather inputs. This is a consideration for Lake Ontario and
St. Lawrence River levels that are controlled based on multiple, sometimes-competing
objectives (hydropower supply, commercial navigation, water supply,
recreational boating, flood and low water level management, and habitat
enhancement) as well as northern lakes in ‘cottage country’ where levels are
also controlled based on a range of objectives.
Strategies for Achieving Sustainable Flood Resiliency
The Ontario government
has set a framework for achieving resiliency through acts, regulations and
guidelines that support municipalities in evaluating resiliency, reporting
infrastructure performance, and planning necessary improvements in level of
service with long-term asset management strategies[xxi]. While the focus is
often on climate change resiliency, significant opportunities for risk
reduction lie in improving resiliency to today’s climate given historical
design limitations and recent growth pressures. Focusing on today’s
infrastructure investment challenges should be pursued as an effective strategy
for achieving flood resiliency today while also delivering future climate
resiliency as a co-benefit. In other words, necessary ‘design standard
upgrades’ can achieve ‘climate adaptation’ goals as well.
There are
opportunities for promote how appropriate safety factors can be incorporated
into design standards to guide municipalities when considering future climate
resiliency - this may require the collaboration of several ministries that are
responsible for interrelated natural hazards (river flood risks), stormwater
management (urban flood risks), and building standards (property-scale risks)
and that affect flooding from ‘flood plain to floor drain’.
OSPE has recently commented
on emerging policies related to flood risks and stormwater management in
Ontario, addressing flood risk factors and highlighting challenges for
achieving sustainable mitigation. OSPE's 2017 report “Weathering the Storms:
Municipalities Plead for Stormwater Infrastructure Funding”[xxii] prepared with the
Ontario Sewer and Watermain Construction Association and the Residential and
Civil Construction Alliance of Ontario identified that “significant investments
will be required to maintain or bring municipal stormwater infrastructure up to
a good or better condition rating” and noted that there is considerable
apprehension on climate change effects among Ontario municipalities. A strategy
that focuses on today’s risks would effectively address future effects and one
that implements technically-effective and cost-effective infrastructure
solutions would ensure that the significant investments would be worthwhile.
What is the Role of Grey and Green Infrastructure?
To help guide
infrastructure priorities OSPE has commented on Ontario’s draft Watershed
Planning Guidance identifying concerns with the effectiveness of emerging
technologies to address flood risks[xxiii]. In earlier comments
on Ontario’s Long Term Infrastructure Plan OSPE recommended that comprehensive
cost analysis was required for green infrastructure (low impact development
measures, like rain gardens, permeable pavement, infiltration trenches, etc.)[xxiv]. The need to evaluate
both technical and cost effectiveness of green infrastructure is especially
important today as it is being promoted in emerging Ontario policies
surrounding stormwater management, and is currently being promoted by several
groups, especially within the insurance industry[xxv], as a viable solution to
achieving flood risk reduction. Often this promotion is being done based on
limited technical input, sometimes with gross economic proxies used in place of
necessary engineering analyses[xxvi].
Analysis of the
cost-effectiveness of various infrastructure solutions for reducing flood
damages has been completed to reinforce the need for comprehensive financial
analysis to further guide infrastructure policies and priorities. Full
lifecycle costs of traditional grey infrastructure (i.e., storm sewers and
sanitary sewers) and emerging green infrastructure solutions were evaluated
considering both initial capital and on-going operation and maintenance costs.
In the case study, grey infrastructure was shown to be cost-effective at
reducing flood damages – in fact for every dollar invested in sewer upgrades, two
dollars of insured damages are prevented. When total losses are considered,
grey infrastructure prevents five dollars of damage. A more important finding
was that the effectiveness of grey infrastructure was one to two orders of
magnitude higher than green infrastructure[xxvii]. These are important
observations to guide infrastructure investments in Ontario as part of asset
management plans, or other flood control strategies. Firstly, grey
infrastructure investments are absolutely worthwhile and can increase the level
of service at a reasonable cost. Secondly, green infrastructure appears to have
been oversold as a potential tool for flood risk reduction, delivering only
pennies of benefits for every dollar spent.
Promoting green
infrastructure as a flood mitigation solution for critical infrastructure is now
pervasive, especially from the insurance industry. Recently, executives from
Intact Financial and Sun Life suggested the need to “improve and even transform
the design, delivery, efficiency, resilience and greening of infrastructure
projects”[xxviii]. This appears to be a counter-productive
approach, as green infrastructure spending represents a significant opportunity
cost considering more cost-effective traditional infrastructure measures.
Furthermore, OSPE’s comments on Ontario’s draft Watershed Planning Guidance
cautioned that green infrastructure can make flooding worse:
“The adverse impacts of green infrastructure infiltration on wastewater
systems, in which the
majority of flooding in Ontario is concentrated due to historical
municipal servicing practices and
standards, has been overlooked in the statement promoting green
infrastructure as a flood
control measure.”
What is the Role of Ontario’s Professional Engineers?
Just as OSPE asserted
that the government must restore the oversight of professional engineers in the
detailed planning and design of Ontario’s power grid to prevent missteps from
happening[xxix],
OSPE asserts the role of professional engineers in the development of
infrastructure investment priorities to mitigate flood impacts in a
cost-effective and timely manner. To identify these investments, Ontario’s
Municipal Engineers Association has a well-established Class Environmental
Assessment process[xxx] for guiding
municipalities in developing master plans and local projects to address local
flooding issues in existing communities. The process evaluates cost, social,
technical and environmental considerations and can be followed to identify
appropriate infrastructure investments. Ontario’s professional engineers can
ensure that appropriate technologies are evaluated and selected, planned and
funded, and then designed and implemented – such infrastructure can provide
flood protection to Ontario communities and lasting value to residents and
businesses who fund these investments through municipal taxes, in some cases
stormwater utility fees.
[i]
Isabella O’Malley. Canada in 2030: New normal of extreme weather events.
September 7, 2018. https://www.theweathernetwork.com/news/articles/canada-in-2030-climate-change-commitments-up-in-the-air-carbon-dioxide-air-quality-humidity-pollen-allergies/111767
[ii]
James Matthews, The Toronto Star. Searchers brace for tragedy after child swept
from mother’s arms into raging Grand River. February 21, 2018. https://www.thestar.com/news/gta/2018/02/21/car-plunges-into-grand-river-near-orangeville-police-emergency-services-search-river.html
[iii]
IBC-ICCA-IISD. Urgent action needed to curb possible debilitating loss of
natural infrastructure assets in Canada: IBC/Intact Centre/IISD Report. http://www.ibc.ca/on/resources/media-centre/media-releases/urgent-action-needed-to-curb-possible-debilitating-loss-of-natural-infrastructure-assets-in-canada
[iv]
Barry J. Adams, Fabian Papa. Urban Stormwater Management Planning with
Analytical Probabilistic Models, ISBN: 978-0-471-33217-6
[v]
Trevor Dickinson, Ramesh Rudra, Kishor Panjabi. Climate Change & Urban
Development Have Impacted Streamflows in Southern Ontario. September 27, 2018. https://www.slideshare.net/RobertMuir3/climate-change-urban-development-have-impacted-streamflows-in-southern-ontrio/RobertMuir3/climate-change-urban-development-have-impacted-streamflows-in-southern-ontrio
[vi]
Statista. Gross domestic product of Ontario, Canada from 2000 to 2017 (in
million chained 2007 Canadian dollars). https://www.statista.com/statistics/577539/gdp-of-ontario-canada/
[vii] Trevor
Dickinson and Ramesh Rudra. Disentangling Impacts of Climate & Land Use
Change on Quantity & Quality of River Flows in Southern Ontario. Undated.
https://www.slideshare.net/RobertMuir3/disentangling-impacts-of-climate-land-use-change-on-quantity-quality-of-river-flows-in-southern-ontario-trevor-dickinson-ramesh-rudra-university-of-guelph
[viii]
The Huffington Post Canada. Toronto Flood: Ferrari Abandoned In Tunnel
(TWITTER). July 9, 2013. https://www.huffingtonpost.ca/2013/07/09/toronto-flood-ferrari-video_n_3566474.html
[ix]
Genivar. Investigation of Chronic Basement Flooding, Eastern Beaches (Area 32),
Final Project File. Section 6 Assessment of Existing Systems. May, 2012. https://drive.google.com/open?id=1qYHDRAxm0JpvQzjHG36OBAs2Y6BpH9JD
[x]
Robert Muir. Basement Underpinning and Sewer Back-up Risks - How Lowering
Basements Increases Flood Damage Potential in Canadian Cities Undergoing
Intensification. July 27, 2018. https://www.cityfloodmap.com/2018/07/basement-underpinning-and-sewer-back-up.html
[xi]
Jennifer Wells. Climate change: How Toronto is adapting to our scary new
reality. The Toronto Star. August 19, 2012. https://www.thestar.com/news/insight/2012/08/19/climate_change_how_toronto_is_adapting_to_our_scary_new_reality.html
[xii]
The Metropolitan Toronto and Region Conservation Authority. A History of
Flooding in the Metropolitan Toronto and Region Watersheds. Undated. https://drive.google.com/file/d/1-IfCxFRoOUwj2OLHhcCVtAKXB9IvdfY2/view
(review of wash-out trends: https://www.cityfloodmap.com/2018/05/is-climate-change-making-flooding-worse_19.html)
[xiii]
Robert Muir. Evidence Based Policy Gaps in Water Resources: Thinking Fast and
Slow on Floods and Flow. Journal of Water Management Modeling. 2018. https://www.chijournal.org/C449
[xiv]
Robert Muir. GO Train flooded in 1981 too. Media misses mark suggesting new
normal for extreme weather and flooding. https://www.cityfloodmap.com/2017/05/go-train-flooded-in-1981-too-media.html
[xv]
Ontario Society of Professional Engineers. Response to Ontario’s Draft
Watershed Planning Guidance 2017 (5) Climate Change Extreme Weather Risks in
Ontario, page 12). April 7, 2018. https://drive.google.com/open?id=1dNFzxZxlzxUx-g9DzvVHSvwceXhddkCq
[xvi]
Ramesh Rudra et.al.. Changes in Rainfall Extremes in Ontario. International
Journal of Environmental Research. July, 2015. https://drive.google.com/open?id=1AngUYFFlm-RqQlmSC0gZqxy8nV61BW8J
[xvii]
Poulomi Ganguli and Paulin Coulibaly. Assessment of Future Changes in
Intensity-Duration-Frequency Curves for Southern Ontario using North American
(NA)-CORDEX Models with Nonstationary Methods. https://arxiv.org/ftp/arxiv/papers/1706/1706.00122.pdf
[xviii]
CBC News. The National. How climate change and extreme weather will change how
we live. September 19, 2018. https://www.youtube.com/watch?v=HuE4oMQyu5k
[xix] Charles
Brindamour and Dean Connor. Climate resilience must be part of every
government’s agenda. The Globe and Mail. September 25, 2018. https://www.theglobeandmail.com/business/commentary/article-climate-resilience-must-be-part-of-every-governments-agenda/
[xx]
Robert Muir. Toronto Island Flooding 2017 - Were Lake Ontario Levels Extreme?
No, Barely Above Historical Maximum Levels. September 30, 2017. https://www.cityfloodmap.com/2017/09/toronto-island-flooding-2017-were-lake.html
[xxi]
Robert Muir. Extreme Weather Resiliency and Climate Adaptation Through
Strategic Asset Management & Infrastructure Investments. Association of
Municipalities Ontario 2018 Annual Conference. August 21, 2018. https://www.slideshare.net/RobertMuir3/extreme-weather-resiliency-and-climate-adaptation-through-strategic-asset-management-infrastructure-investments
[xxii]
Ontario Society of Professional Engineers, The Residential and Civil
Construction Alliance of Ontario , and The Ontario Sewer and Watermain
Construction Association. Weathering the Storms: Municipalities Plead for
Stormwater Infrastructure Funding. 2017. https://www.ospe.on.ca/public/documents/reports/Stormwater-report-2017-compressed.pdf
[xxiii]
Ontario Society of Professional Engineers. Response to Ontario’s Draft
Watershed Planning Guidance 2017. April 7, 2018.
https://drive.google.com/open?id=1dNFzxZxlzxUx-g9DzvVHSvwceXhddkCq
[xxiv]
Ontario Society of Professional Engineers . Engineers Respond to Ontario's
Long-Term Infrastructure Plan 2017 (EBR 013-1907). January 27, 2018.
[xxv] About
Insurance Bureau of Canada, Intact Centre on Climate Adaptation, and
International Institute for
Sustainable Development. Combatting Canada’s Rising
Flood Costs: Natural infrastructure is an underutilized option. September,
2018. http://assets.ibc.ca/Documents/Resources/IBC-Natural-Infrastructure-Report-2018.pdf
[xxvi]
pwc in collaboration with Autocase. Assessing the business case for green
infrastructure through a Total Economic Valuation approach, Final Draft.
November, 2017. https://drive.google.com/open?id=1VoJiXMG4jh1KyfCBizIwAd9Yv9Dkf5A2
[xxvii]
Robert Muir and Fabian Papa. Economic Analysis of Flood Damage Reduction for
Grey and Green Infrastructure – Cost Benefit Analysis Considering Insured and
Total Losses, Erosion Remediation Offsets, Lost Productivity Value, and
Willingness to Pay for Surface Water Quality Improvements. September 17, 2018. https://drive.google.com/open?id=1IsMZOrMZaRf6HMs8ubbVsY866daPjkiV
[xxviii]
Charles Brindamour and Dean Connor. Climate resilience must be part of every
government’s agenda. The Globe and Mail. September 25, 2018. https://www.theglobeandmail.com/business/commentary/article-climate-resilience-must-be-part-of-every-governments-agenda/
[xxix]
Ontario Society of Professional Engineers. Ontario Wasted More Than $1 Billion
Worth of Clean Energy in 2016. Society Notes, The official blog of the Ontario
Society of Professional Engineers. June 29, 2017. https://blog.ospe.on.ca/featured/ontario-wasted-more-than-1-billion-worth-of-clean-energy-in-2016-enough-to-power-760000-homes/
[xxx]
Municipal Engineers Association. Municipal Class Environmental Assessment
(MCEA). October 2000, as amended in 2007, 2011 & 2015. http://www.municipalclassea.ca/
***
On the question of "Are Storms Bigger and More Frequent Due To Climate Change?" - the CBC Ombudsman has recently consulted Environment and Climate Change Canada (ECCC) in response to complaints on reporting inaccuracy and ECCC indicated: “For Canada as a whole, observational evidence of changes in extreme precipitation is lacking.”
CBC has corrected their original reports that claimed 100-years storms were increasing, as detailed in the earlier post: CBC articles corrected
ECCC has confirmed the observation that extreme precipitation has not changed in across Canada in its recent Canada's Changing Climate Report which states: "For Canada as a whole, there is a lack of observational evidence of changes in daily and short-duration extreme precipitation.", and "There do not appear to be detectable trends in short-duration extreme precipitation trends in Canada as a whole based on available stations data."
CBC has corrected their coverage on this ECCC report in this article saying "Correction - An earlier version of this story said that more intense rainfall contributes to increased urban flooding. In fact, while the report states that precipitation is higher overall, it did not find that episodes of short-duration extreme rainfall have increased or establish a connection between these and increased or exacerbated flooding."
Our review of the most current Engineering Climate Datasets (Version 3.0) shows that in southern Ontario, design rainfall intensities continue to decrease since 1990 - see review of IDF trends long term climate stations. Overall, frequent storm intensities (i.e., 2 Year storms) and infrequent storm intensities (i.e., 100 Year storms) have decreased in intensity - frequent storms, those we have observed the most and have the most confidence in trends, have decreased the most.
ECCC has confirmed the observation that extreme precipitation has not changed in across Canada in its recent Canada's Changing Climate Report which states: "For Canada as a whole, there is a lack of observational evidence of changes in daily and short-duration extreme precipitation.", and "There do not appear to be detectable trends in short-duration extreme precipitation trends in Canada as a whole based on available stations data."
CBC has corrected their coverage on this ECCC report in this article saying "Correction - An earlier version of this story said that more intense rainfall contributes to increased urban flooding. In fact, while the report states that precipitation is higher overall, it did not find that episodes of short-duration extreme rainfall have increased or establish a connection between these and increased or exacerbated flooding."
Our review of the most current Engineering Climate Datasets (Version 3.0) shows that in southern Ontario, design rainfall intensities continue to decrease since 1990 - see review of IDF trends long term climate stations. Overall, frequent storm intensities (i.e., 2 Year storms) and infrequent storm intensities (i.e., 100 Year storms) have decreased in intensity - frequent storms, those we have observed the most and have the most confidence in trends, have decreased the most.
