Showing posts with label toronto. Show all posts
Showing posts with label toronto. Show all posts

Toronto Extreme Rainfall Trends - 100-Year Daily Rainfall in Engineering Climate Datasets

Previous posts have reviewed trends in extreme rainfall across Canada, in various regions including southern Ontario, and in the Greater Toronto Area (GTA), including Toronto and Mississauga where long-term climate data is available for review.

Projections of future extreme rainfall increases are commonly made as part of climate change studies. A review of past trends in extreme rainfall was made in the 2021 National Research Council flooding cost benefit guidelines, as summarized in a previous post. The following chart was included in those guidelines and shows the trends in 100-year daily rainfall at two GTA climate stations in downtown Toronto and at Pearson International Airport in the adjacent municipality of Mississauga.

Toronto 100-Year Rainfall Trends and Projections

The chart shows the 100-year rainfall depth using data records up to 1990 and then adding more recent data up to 2017. The chart shows that the 100-year rainfall at Pearson Airport/Mississauga has been decreasing slightly when recent data is added after 1990. Meanwhile the Toronto rainfall has been increasing slightly (see dotted and dashed black lines on the chart above for the trends).

Several climate studies have projected that the 100-year daily rainfall would increase over coming decades as shown on the chart. The Toronto's Future Weather & Climate Driver Study by SENES projected a doubling of this rainfall statistic by 2040-2049, relative to a 2000-2009 baseline value (see the orange dashed line on the chart above, where the 2000-2009 value is shown at 2005 and the 2040-2049 value is shown at 2045).

Some additional data has been analyzed by Environment and Climate Change Canada for the Toronto climate station, now including data up to 2021. This allows the 100-year daily rainfall statistic to be updated with a few more years of data. The chart below shows the additional Toronto data point circled in yellow at 2021.

100 Year Daily Rainfall Trends in Toronto and Mississauga and Climate Projections

While the Toronto rainfall statistic up to 2017 was 97.5 mm, the value up to 2021 decreased slightly to 97.3 mm. The value up to 2017 reflected the prior July 8, 2013 extreme event, creating a jump after 2007 when the value was slightly lower at 94.7 mm. As more data is observed below the 2013 extreme, the statistic should continue to decrease as more data is added and analyzed.

The take-away? Observational data, including data up to 2021, does not support the projected significant increases in 100-year daily rain in climate studies. The Toronto data is available over the period of 1940 to 2021.

How far off are the projected increases in extreme rainfall? The Toronto Future Weather & Climate study projected a theoretical 31mm/decade increase over 40 years - that was for Pearson Airport climate station. Actual data at Pearson Airport shows an observed increase of only 3.1mm/decade.  This considers a value of 115.1 mm in the middle of the 1950-2003 period and a value of 125.5 mm for 2003-2017 - that later value is estimated to generate the current value of 117.3 mm by using a weighted average across all years from 1950 to 2017. For Toronto the actual increase is only 2.0 mm/decade.

On average the GTA (Toronto and Pearson/Mississauga) increase is about 2.5 mm/decade, or less than a tenth of almost 31mm/decade projected in the SENES climate/future weather study.

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Further reading in previous posts on extreme rainfall trends:

1) Rainfall intensity trends in Canada:

a) 226 long term climate stations in the Engineering Climate Dataset are used to show actual trends between rain intensity statistics up to 2007 and then up to 2017: https://www.cityfloodmap.com/2020/12/design-rainfall-trends-in-canada.html

b) more of the above plus observed annual maxima rainfall trends as reported in the 2021 National Research Council of Canada (NRC) "National Guidelines on Undertaking a Comprehensive Analysis of Benefits, Costs and Uncertainties of Storm Drainage and Flood Control Infrastructure in a Changing Climate": https://www.cityfloodmap.com/2022/02/nrc-national-guidelines-on-flood.html

2) Rainfall intensity trends in Southern Ontario:

a) ECCC's Engineering Climate Dataset Intensity Duration Frequency (IDF) trends for long-term southern Ontario climate stations, comparing statistics up to 1990 and current values (v3.3 datasets with some station data up to 2021): https://www.cityfloodmap.com/2023/05/southern-ontario-extreme-rainfall.html

3) Rainfall extreme reporting (?) in the media (including Toronto, Mississauga trend review):

a) Thinking Fast and Slow About Extreme Weather and Climate Change, inspired by the late Daniel Kahneman (RIP good sir), exploring the cognitive biases in extreme rainfall reporting in the media: https://www.cityfloodmap.com/2015/11/thinking-fast-and-slow-about-extreme.html

b) my paper with "Thinking Fast and Slow" themes published in the Journal of Water Management Modelling with the title "Evidence Based Policy Gaps in Water Resources: Thinking Fast and Slow on Floods and Flow": https://www.chijournal.org/C449



4) Local studies that observed no increases in design rainfall when updating IDF values:


While media and the insurance industry has repeated that climate change has been responsible for increased flood damages and insurance claims over past decades, the lack of increases in extreme rainfall means that other factors are at play. These include fundamental changes in hydrology in urbanized communities, e.g., increased watershed development and intensification. See previous posts for some examples of expanding urbanization in Ontario communities over previous decades: https://www.cityfloodmap.com/2016/08/land-use-change-drives-urban-flood-risk.html

When fact checkers look into media statements regarding extreme rainfall trends, including the CBC and Radio Canada Ombudsmen offices, data shows no overall increase in extreme rain across Canada. This post shares corrections made by the CBC over recent years: https://www.cityfloodmap.com/2019/06/cbc-correcting-claims-on-extreme.html

Toronto Area Extreme Rainfall Intensity Trends - Environment Canada IDF Curve Updates 2020

Environment and Climate Change Canada's intensity duration frequency (IDF) data describes the rare extreme rainfall intensities used to design drainage infrastructure and to assess river peak flows/flood flows when the big storms hit.

Some climate station IDF analysis have been due for an update for several years.  The new version 3.10 update in 2020 extends analysis to 2016-2017 in many cases.  The trends in short duration intensities can show how flood risks are changing due to changing climate and any more severe weather. Many municipalities and researchers have updated their IDF statistics internally and have reported trends in extreme rainfall intensities (see previous post for Ontario studies: https://www.cityfloodmap.com/2020/05/annual-maximum-rainfall-trends-in.html).

Earlier versions of the IDF datasets are available to characterize annual maximum rainfall, dating back to 1990.  The tables below shows updated trends in 100-year rainfall intensity over a short 5 minute duration at Buttonville Airport in Markham (updated in version 3.10 in 2020) and in Toronto and Mississauga (updated in version 3.10 in 2019).





For short durations, it appears that extreme rainfall intensities are decreasing in the Greater Toronto Area.  The rare 100-year intensities are decreasing from 4-7% at the three locations above.  The more frequent 2-year intensities are decreasing by about 5-8%.

There is higher uncertainty with 100-year storm intensities due the rarity and spatial distribution of events.  However, the more frequent 2-year intensities that rely on many more rainfall observations every year to characterize these average annual peaks are more reliable.  To illustrate this, consider the 95% confidence bands on the Environment Canada IDF 5-minute data for Buttonville Airport, in southern York Region, just north of Toronto:
Extreme Rain 95% Confidence Bands Buttonville Airport, Markham, Ontario - Environment Canada Engineering Climate Datasets v3.10
The 100-year 95% confidence band of 97 mm/hr (2 x 48.5) is 46% of the expected value of 210.8 mm/hr.  In contrast, the 2-year band of 22.6 mm/hr is only 22% of the expected value of 104.7 mm/hr, a relatively tighter band.  The tight band makes the observed decrease in 2-year rain intensities more noteworthy, i.e., the 2-year intensity has decreased 7.6% which is a significant proportion of the uncertainty band.

The longer duration annual maximum rainfall series for Toronto and Mississauga have relatively tighter confidence bands for both 100-year and 2-year intensities:

Extreme Rain 95% Confidence Bands Pearson International Airport, Mississauga, Ontario - Environment Canada Engineering Climate Datasets v3.10

Extreme Rain 95% Confidence Bands Toronto, Ontario - Environment Canada Engineering Climate Datasets v3.10

Given that rainfall intensities are decreasing over most durations in the Greater Toronto Area, based on Environment Canada's annual maximum series and derived 2-year and 100-year IDF design intensities, why does media often report a 'new normal' of more extreme weather?  This may be due to lack of familiarity with data and a tendency to exercise an 'availability bias', i.e., simple listing of recent events that have caused damages and association of those events with increasing rainfall intensities, but without checking the actual rainfall trends or investigating other factors.  For more on cognitive biases in framing and solving complex problems read about Thinking Fast and Slow on Floods and Flow:   https://www.chijournal.org/C449.   Given the proliferation of rainfall gauges across the GTA, many more than the Environment Canada numbers, the observation of many extreme events over a short duration may not be a statistical anomaly at all, as analysis here shows: https://www.cityfloodmap.com/2019/03/are-six-100-year-storms-across-gta-rare.html

The CBC has made several corrections to its stories on changing extreme rainfall trends in the past, sometimes finding violation of its Journalistic Standards and Practices regarding accuracy of reporting - here are some examples: https://www.cityfloodmap.com/2019/06/cbc-correcting-claims-on-extreme.html.  Most recently the CBC Ombudsman in a review entitled "Past, Present, or Future" wrote that "journalists could have been clearer with their choice of tenses" - more on that here: 

The CBC Ombudsman stated "There are appropriate distinctions made between observed phenomena and predicted phenomena" in its reporting noting this excerpt: 
  • Precipitation will increase in much of the country.
  • Weather extremes will intensify.
The last two bullet points are careful to use the future tense.

The recently updated Environment Canada IDF data in the GTA supports the CBC's perspective that intensified weather extremes are predicted phenomena as opposed to observed ones.




Annual Maximum Rainfall Trends in Canada - Environment Canada Engineering Climate Datasets v3.10 Update

A recent post (https://www.cityfloodmap.com/2020/02/annual-maximum-rainfall-trends-in.html) reviewed trends in annual maximum rainfall, their direction and statistical significance (i.e., showing whether the trends strong or are mild and just reflect normal variations).

Now there is an update. Environment and Climate Change Canada has just released v3.10 of the Engineering Climate Datasets that include annual maximum series data used to derive IDF curves, as well as the trends in those annual maximum series.  (note: trend data are contained in the comma delimited text file idf_v-3.10_2020_03_27_trends.txt in the IDF_Additional_Additionnel_v3.10.zip file on the Environment Canada download site).

Overall many additional stations have been added to the trend analysis.  Version 2.30 had 565 stations, Version 3.00 had 596 station and Version 3.10 now has 651 station.  The average length of record is 25.5 years.  How have the trends in annual maximum rainfall changed? The 3 charts below show that the change is very gradual, there are more significant increases than decreases, but overall the percentage of non-significant trends is unchanged.

Annual Maximum Rainfall Trends in Canada Environment Canada Engineering Climate Datsets
Maximum Rainfall Trends in Canada - Engineering Climate Datasets v3.10, v3.00 and v2.30, Environment and Climate Change Canada
The summaries at the bottom show:

Trend in Maximum Rain   v3.10        v3.00         v2.30
Significant Increase            4.28%      4.18%        4.09%
Significant Decrease           2.24%      2.33%        2.30%
No Significant Trend        85.80%     85.55%      86.37%
No Calculation                    7.68%      7.94%        7.24%

How about regional trends? Some provinces have more decreases than increases:

annual maximum rainfall environment canada data trends
Annual Maximum Rainfall Trends in Canada, by Province / Region - Environment and Climate Change Canada Engineering Climate Datasets v3.10 (March 2020)


Trends in the Toronto area are shown on the following charts for the City of Toronto, City of Mississauga (Pearson Airport), and City of Markham (Buttonville Airport).

City of Toronto Annual Maximum Rainfall Environment Canada
Toronto Maximum Rainfall
City of Mississauga Annual Maximum Rainfall Environment Canada
Mississauga Maximum Rainfall

Markham York Region Maximum Rainfall Annual Maximum Rainfall
Markham, York Region Maximum Rainfall

Trends in Toronto indicate annual maximum rainfall is decreasing for all durations from 5 minutes to 24 hours.  The decrease for the 12 hour duration is statistically significant.

Trends in Mississauga at Pearson Airport are decreasing for most durations, however the 1 hour duration trend is increasing due to the July 8, 2013 peak.  No Mississauga trends are significant.

Trends in Markham, in southern York Region are decreasing for shorter durations of 30 minutes or less and increasing for longer durations. None of the trends are significant.





Toronto and Mississauga Lost Rivers and Urban Flooding

Just a few GIS maps illustrating urban flooding risks in Toronto and Missisauga, showing lost rivers and historical flooding locations (Toronto May 2000 [orange symbol] and Toronto August 2005 [red symbol] storms and Mississauga July 2013 [yellow symbols]).  The lost river major overland flow paths for small catchments (less than 1000 hectare drainage area) are estimated using the rationale method with the SOLRIS Version 2 land use-derived runoff coefficients, times of concentration derived from the MNRF WRIP enhanced DEM to estimate peak rainfall intensity, and approximate uniform flow depth and spread approximations along the centreline flow path. The land use shown is the province of Ontario's SOLRIS Version 3 data, which helps show where overland flow paths are in channels, open spaces, parks and easements vs. through developed areas where original drainage features have been enclosed over time.

Toronto - East End: good slopes toward Lake Ontario, the Don River valley and Taylor Creek. Little flooding in May 2000 and August 2005 (those storms did not affect this area greatly however).

Lost Rivers Toronto Flood Pluvial Flooding Beaches East York Riverdale Leslieville

Toronto - West End: a few flood clusters along the lost river flow paths.

Lost Rivers Toronto Flood Pluvial Flooding Etobicoke

Toronto - North End (Newtonbrook area): significant flooding in low relief areas, clusters of flooding along other lost river flow paths. Highest concentration of flooding area in 'partially separated' sewer servicing areas where foundation drains contribute wet weather flow to the wastewater collection system and overland flow paths were not explicitly designed.

Lost Rivers Toronto Flood Pluvial Flooding North York Newtonbrook

Mississauga - Malton Area: Older development, less resilient servicing standards.  Flooding locations are approximate but appear to show concentration along the downstream end of the large central 'lost river', north of the 401.

Lost Rivers Mississauga Flood Pluvial Flooding Malton

Mississauga - Cooksville Creek: A large 2000 mm diam. trunk sewer runs along the 'lost river' flow path in the centre of the map, south the the QEW.  This branches to two large trunk under the QEW and upstream.  Flooding locations are approximate.

Lost Rivers Mississauga Flood Pluvial Flooding Cooksville Creek

Toronto Area Extreme Rainfall Trends - Comparing Engineering Climate Datasets with Future Weather & Climate Study Predicted Trends

Environment and Climate Change Canada's Engineering Climate Datasets summarize observed annual maximum rainfall over various durations from 5 minutes to 24 hours.  Theses series are used to derive IDF tables and charts that describe the intensity, duration and frequency (i.e., return period) of extreme rainfall.  IDF tables are used to support engineering design of storm drainage and wastewater systems, and are used to define rainfall patterns used in hydrologic modelling.

The City of Toronto commissioned Toronto's Future Weather & Climate Driver Study - the 2012 results indicate projected changes in extreme rainfall for a few durations and return periods.  Results of the Outcomes Report are here https://www.toronto.ca/wp-content/uploads/2018/04/982c-Torontos-Future-Weather-and-Climate-Drivers-Study-2012.pdf.  The baseline period for the study is 2000-2009 and statistics are predicted out to 2040-2049.

The Engineering Climate Datasets have been updated in early 2019, including for two Toronto-area climate stations with long records called "Toronto City" and "Toronto International Airport".  The following tables compares the predicted increase in extreme rainfall in the 2012 study with trends in the same statistics from 1990 to 2017 at these two Toronto-area stations.



A key take away is that the Future Weather & Climate Driver Study does not agree with the direction and magnitude of changes in the actual statistics, which are based on real observations (not modelling predictions).  Some actual statistics have been decreasing since 1990, not increasing as predicted int eh study.  When a statistic is increasing, it is at a significantly lower rate that what is predicted in the study.

The following chart compares the past 100 year daily data to the study predictions - the Toronto study seems to have a hockey stick shape, jumping significantly upward by the 2040's which does not match the past trends.


The next chart shows changes in 10 year hourly rainfall. The Toronto study significantly understates the value today, suggesting it will double by the 2040's - the predicted future value has already been in place since the 1990's however.


It is questionable whether the City of Toronto should consider any changes to design criteria for municipal infrastructure considering these future predictions - best to follow ASCE's approach and incorporate flexibility in future design and wait and see with the 'observational method'? - if observations show that there is no change in the statistics, there should be no significant driver in changing design criteria, especially based on models that do not match the magnitude or trend in actual extreme rainfall statistics.

***

Bonus: here are a few more predicted 24 Hour 100 Year rainfall values, also going against the observed trends:


Are More 100 Year Storm Happening? Yes and No. A Proliferation of Rain Gauges Can Now Record More 100 Year Storms, But Fixed Locations Show No Increase

There are many sensational media stories about ghost storms and ninja storms hitting urban areas, and a steady claim that we are experiencing more extreme rainfall, that is, higher intensities for a given probability (called return period), or greater frequency of given design intensities. Often it is stated that we are experiencing more 100 year storms today and that is a "new normal" brought on by a changing climate.

How does the number of climate stations, or rain gauges, that are in operation affect the number of observed extreme events. Well, let's look at Toronto for example.  Several past extreme events were reported in the Staff Report on Impact of July 8, 2013 storm on the City's Sewer and Stormwater Systems dated September 6, 2016: (https://www.toronto.ca/legdocs/mmis/2013/pw/bgrd/backgroundfile-61363.pdf)

During the May 12, 2000 extreme rainfall event, Toronto operated 16 rain gauges as shown on the staff report map below.


Fifteen years later, during the August 19, 2005 storm, the City operated 31 rain gauges as shown below, so almost double the number of rain gauges.  Look at the higher density of gauges in north Toronto where many higher August 19, 2005 rainfall depths were observed.

Then 8 years later, during the July 8, 2013 storm the city operated even more rain gauges, i.e., 35 in total.


And then a few years later, on August 7, 2018, the city operated 43 rain gauges - even more than 2013. I don't have a map but here is a super-cool graph summarizing Toronto Open Data rainfall totals at those gauges over a period of 5 minutes to 24 hours.


And now today as of July 17, 2019, Toronto has 45 active rain gauges as shown in the following map presented to the Ministry of Environment Conservation and Parks' stormwater stakeholder group participating in development of minimum standards for ECA pre-approval.


So let us summarize the trend in the number of rain gauges in the chart below.


Astute blog readers will notice that the number of rain gauges has increased almost 300% since the year 2000. Yes, almost three times the number of rain gauges now. Obviously, more extreme events can be observed and recorded when the number of rain gauges increases dramatically.

The following table shows that in the year 2000, there was a rain gauge every 39.4 square kilometres (16 gauges per 630.2 square kilometres). By 2019, there is a gauge ever 14 square kilometres.


***

So what is happening at fixed locations where rain intensities are measured? In Toronto and Mississauga, many trends are downward according to the Engineering Climate Datasets:

 

As a result, design intensities for short durations have been decreasing since 1990:


***

To recap, many more rain gauges today mean we 'see' more storms - these are typically needed to support basement flooding Municipal Class EA studies (rainfall needed to calibrate hydrologic and hydraulic simulation models), to guide operational activities too.  Many municipalities have installed rain gauges to support inflow and infiltration management programs.

We have a "finer mesh net" to catch these events and add them to our records - we have almost 3 times more rain gauges in Toronto since 2000.

But no. Storm are not becoming more intense. If we see more of them, it is because we are looking harder for them with more extensive monitoring efforts. Given this expanding intensive network of rain gauges today, it is not uncommon, statistically speaking, to observe many 100-year storms over a short time period.  This earlier post explores those statistics in the GTA - https://www.cityfloodmap.com/2019/03/are-six-100-year-storms-across-gta-rare.html.

Disaster Mitigation Adaptation Fund - Infrastructure Canada Announces Toronto, Vaughan , Markham, Regional Municipality of York Grants

Disaster Mitigation Adaptation Fund (DMAF) funding has been announced for Alberta and Ontario - the announcement for GTA municipalities has been made March 26.  Funding in the City of Toronto, City of Vaughan and the City of Markham is focused on earlier development areas with limited design standards for municipal infrastructure and limited land use planning surrounding floodplain hazard management. The total funding is $150,388,000.

The Markham projects fall under its long term Flood Control Program and include sewer upgrades in the West Thornhill community where Phase 3 and Phase 4 are being 40% funded through DMAF, the Don Mills Channel flood control upgrades including a central wetland storage/floodplain restoration will replace vulnerable properties to be purchased as well as culvert upgrades, and sewer upgrades in the vicinity of the Thornhill Community Centre which will reduce flood risks for vulnerable populations. Details on the West Thornhill Project are here: link, and the Don Mills Channel project details are here: link

The Vaughan projects include the Vaughan Metropolitan Centre Black Creek and Edgeley Pond  - details on the project are here: link

The Toronto project involves the Midtown Toronto Relief Storm Sewer that is part of the city's long term and comprehensive Basement Flooding Protection program. The project will help reduce flooding for almost 900 homes during a 100-year flood event. See details on the overall program here: link

The Regional Municipality of York project involves the twinning of a wastewater collection system forcemain (pressurized flow). This has been called a a significant component of the Upper York Sewage Solutions project. See project details here: link

*** ANNOUNCEMENT ***

Canada helps protect communities across the Greater Toronto Area from flooding
and storms

Four new projects approved in four communities in the City of Toronto and the Regional Municipality of York

Climate change is happening and it is affecting Canadian communities from coast-to-coast-to-coast. More and more Canadians realize that natural hazards like floods, wildland fires and winter storms are increasing in frequency and intensity. For many communities, these hazards are significantly affecting critical infrastructure and can result in health and safety risks, interruptions in essential community services and increasingly high costs for recovery and replacement.

The Government of Canada’s Disaster Mitigation and Adaptation Fund (DMAF) is a 10-year, $2 billion national program designed to help communities better withstand current and future risks of natural hazards.

The following four projects in the Greater Toronto Area have been approved for federal funding totaling $150,388,299 and for municipal funding totaling $252,682,449.


Location
Project Name
Federal Funding
Municipal Funding
Toronto, City of
Construction of the Midtown Toronto Relief Storm Sewer for Basement Flooding Protection
$37,160,000

$82,840,000     

York, Regional Municipality of
York Durham Sewage System Forcemain Twinning Project
$48,000,000

$72,000,000 

Markham, Corporation of the City of
City of Markham’s Flood Control Project
(Don Mills Channel, West Thornhill, Thornhill Community Centre)
$48,640,000

$72,960,000 

Vaughan, City of
Implementing Vaughan Stormwater Flood Mitigation projects
$16,588,299

$24,882,449 


***

An announcement was made regarding DMAF funding in Edmonton ($53,000,000) for the construction of two dry ponds in Parkallen’s Ellingson Park =-these are two of 13 planned facilities and are expected to reduce the amount of water pooling in the area by about 84 per cent: ink

An announcement was made regarding DMAF funding in Canmore, Alberta ($13,760,000) for a project involves reinforcing flood mitigation structures along several steep mountain creeks in the Bow Valley to reduce the risks of debris flooding, and re-vegetation and bio-engineering work to control erosion problems: link - more on the project here

An announcement was made regarding DMAF funding of the Calgary Springbank Off-stream Reservoir Project ($168.5 million) in Rocky View County which will divert extreme flood flows from the Elbow River to a storage reservoir to be contained temporarily until the flood peak has passed : link . The reservoir would have capacity of over 70 million cubic litres and would be located 15 kilometres west of Calgary between Highway 8 and the Trans-Canada Highway, and east of Highway 22.

More on the Disaster Mitigation and Adaptation Fund and projects: http://www.infrastructure.gc.ca/dmaf-faac/index-eng.html

***

Background on return on investment (ROI) cost benefit analysis to support the Markham DMAF application is here considering its city-wide Flood Control Program that shows a ROI, or benefit cost ratio of over 5 if total losses are mitigated - a lower ROI would result from deferral of only insured losses:



The Markham DMAF project ROI values are based on individual project costs and benefits, with these benefits based on deferred total losses (i.e., higher than insured losses). The average ROI benefit-cost ratio is 4.7 for the three Markham projects.

***

Benefit cost analysis for infrastructure adaptation to extreme weather and climate change using grey and green infrastructure strategies is presented in an upcoming WEAO paper provided in an earlier post: link

Is Climate Change Making Flooding Worse? - Stormy Data Trumps Fake News on Extreme Weather Trends and Flooding

From the Toronto Star: "Once, when he [Environment Canada's Dave Phillips] offhandedly uttered the words “storm porn” in a pre-interview, a TV reporter built a whole segment around the phrase, because there is only one thing editors and the public crave more than a weather story or a sex story, and that is a sexy weather story." link

***

"Stormy Data" is in the news almost daily - the media is obsessed with stories about big rain events and flooding - but sometimes the media is full of "weather porn", i.e., sensational stories and video clips that skew the reality behind severe flooding events. Certainly flooding is a critically important issue across Canada that needs careful and sustained attention to make improvements. But the focus on changing weather as the cause is often incorrect, and the tendency to point to climate change as the cause is equally wrong... Fake News. Fake News! Confused Media!

This post talks about storm porn (sometimes used in insurance marketing), flood loss trends in Canada and the causes, and a history of flooding in the Toronto area that suggests flood events and road/bridge washouts were more frequent in the past before modern floodplain management and design practices. That is good news that Best Practices can reduce flood risk over time!

On Weather - More Extreme? No. Its Storm Porn

Almost 30 years ago we has a cable weather channel that was had simple weather forecasts on the 'tube' (The Weather Network History). Today The Weather Network gives us:

"Force of Nature - (Featured every 20 minutes on the 3's, a show-reel of significant weather making headlines around the world), and Force of Nature Extended segment where a news reporter gives an in-depth description of the footage shown."

and "Storm-Hunters - weekends at 7 and 10pm." and "Angry Planet".... - I call this "storm porn", or "weather porn".

And no fallen limb or large puddle escapes weather reporting. Reporters know to go to the underpasses because they flood in extreme weather ... just like they are designed to - but there is no capacity in weather reporting or mainstream media to even remotely consider these design facts. It is better for business to sensationalize the events. What is better for science and public policy however?

But storms are not bigger or more frequent, or more sever today than they used to be - Environment and Climate Change Canada's Engineering Climate Datasets (Version 2.3) show this, despite what the insurance industry has stated (unfortunately by mixing up predictions with observations, theory with facts, annual precipitation totals with short-duration rain bursts):



Intact Financial Weather Frequency Shift
Intact Financial video promotes disproved 40 year to 6
year weather shift (Telling the Weather Story).
The insurance industry does not properly consider storm/weather data that engineers rely on to assess flood risks and continues to state that "In Canada, weather events that used to occur every forty years are now happening every six years in some regions"  as in this video on their web site/blog. That statement about more frequent weather has been shown to be a 'made-up', theoretical bell-curve shift and not actually real data.




On Flood Causes - Many Factors

Flood incidents are caused by many factors. For example, high risk, historical land use planning:
  1. Gatineau 2017 flooding was due primarily to having 75% of buildings in the 1-in-20 year flood plain, a high risk zone that has a 5% chance of flooding every year.
  2. Toronto Island 2017 flooding was due primarily to not completing the buy-outs of the remaining high risk properties.
Or sometimes operational decisions (mistakes) result in flood incidents. The 2013 GO Train flood is a clear example of known floods risks and inadequate operational care - deeper flooding happened regularly at the stranded train site (even just 6 weeks before), and happened over the span of the line's operation, dating back to the early 1980's. But no operational procedures were in place to check water levels or stop trains from entering the floodplain. When the last train was stranded on July 8, 2013, the Don River Watershed did not receive record rain at all and the river flow was a less than a frequent 1-in-5 year flow rate, something with a 20% chance to occur every year. 

Or sometimes stuff was just built kinda small back in the day. That's right. Infrastructure is just like cars or anything else and used to be built to a lower standard of performance - cars did not have seatbelts or anti-lock brakes and guzzled gas in the 1950's. Similarly, sewer and drainage systems in the 1950's were prone to excess wet weather flow inflow and infiltration (I&I) stresses, inadequate overland flow planning/design, and no river flood hazard mapping or land use regulation.

Or the cumulative effect of urbanization and intensification over a century in urban areas aggravates the issues associated with the factors above. Same old rain results in more flooding.

How many times do we have to say it? "There has been No Collusion between storm frequency and flood frequency". OK, we meant "No Causation", but you get the message.

On Flood Damages / Losses

Damages need to be mitigated. I charted out a Best Practices approach for identifying and mitigating flood risks holistically from 'flood plain to floor drain', looking at riverine, storm and sanitary/wastewater systems in this blog post.

Insured and uninsured losses from catastrophic and relevant events in Canada are charted by Munich RE. These flood losses include categories of hydrologic events and meteorologic events (hurricanes) that are normalized by inflation and growth in GDP to provide an indication of trends over time. The chart below shows flood losses between 1980 and 2017 in Canada:
Canadian Flood Damage Trends Insurance Losses
Canadian Catastrophic and Relevant Event "Flood" Losses, Inflation and Growth Adjusted for Hydrological and Meteorological Events in USD - Prepared by Munich RE NatCatSERVICE.
Losses are creeping up. We do have to address flood risks.

On Flood Frequency - New Normal? Or Old Extremes?

We have a tendency to forget the past. Its not well documented or easy to find.  So this should help.

The Toronto and Region Conservation Authority has documented past flooding in its jurisdiction showing flooding back to 1804 in this undated document called "A History of Flooding in the Metropolitan Toronto and Region Watersheds":

Link to full report.

The report acknowledges that prior to 1850, records of flooding are limited and suggests that many have been lost -  those that survived are in letters and diaries, and do not give a complete picture of past flooding risks.

This is noted in the excerpt below:



Some nice take-aways:

We build better today: "Over the years, road bridges became higher and stronger in response to the changing type and volume of traffic that they were required to carry. Consequently, reports of bridges descruction became rarer over time."

We keep better records today: "... newspapers and other sources tended to record only the most severe events, particularly in areas which flooded almost every spring."

Seems we used to flood A LOT in the past: The number of flood events documented by watershed and tributary/site are listed below. Often small bridges were destroyed but are not listed below. Where major road bridge's were damage and had to be replaced, or where roads washed-out, those events are noted below as "Notable Events". Mill destruction was frequent but is not noted:

Etobicoke Creek Watershed
- Long Branch - 1930 to 1954 - 9 flood events (7 in the spring)
- Brampton - 1854 to 1974 - 22 flood events (13 in the spring)
- Highway 7 at East Branch - 1968 - 1 flood event
- Tributary near Dixie Road and Dundas Street - 1974 - 1 flood event

Total Number of Documented Flood Events = 33
Notable Road and Bridge Destruction Events: 1
- Brampton April 7, 2012 "severe damage to roads, bridges, buildings"

Mimico Creek
- "No flood records have been kept..."
- 2 floods are listed, in 1850 and 1954

Total Number of Documented Flood Events 2

Humber River
- Bloor Street Bridge - 1850 to 1954 - 7 flood events
- Lambton Mills - 10 flood events (5 in the spring)
- Eglinton Flats - 1804 to 1954 - 10 flood events (5 in the spring)
- Weston - 1842 to 1954 - 10 flood events (7 in the spring)
- Albion Road Bridge - 1850 to 1954 - 6 flood events (4 in the spring, Feb-May)
- Thistletown -1878 to 1954 - 4 flood events (2 in the spring)
- Gristmill, Holm, Cord - 1850 to 1893 - 4 flood events (2 in the spring)
- Humber Summit, Rowntree's Mill - 1850 to 1893 - 5 flood events (4 for mill and 1 for subsequent cottages)
- Sawmill J. Brown - 1850 to 1893 - 4 flood events
- Woodbridge - 1878 to 1961 - 19 flood events (13 in the spring)
- Mills on Main Branch - 1850 to 1925 - 6 flood events (5 in the spring)
- Bolton - 1850 to 1972 - 22 flood events (18 in the spring)
- Mills on the Upper Humber River - 1850 to 1909 - 4 flood events (3 in the spring)

Total Number of Documented Flood Events = 111
Notable Road and Bridge Destruction Events5
- Weston, October 15-16, 1954, "Lawrence Avenue Bridge destroyed"
- Eglinton Flats, June 3, 1947. "roads washed out, buildings flooded"
- Humber River, Bloor Street Bridge, Spring 1916 "completely washed out"
- Woodbridge, August 5, 1882 "approaches to bridge on main road washed out"
- Woodbridge, January 13, 1937 "roads flooded and some washed out"

Black Creek
- Floodplain near Mt. Dennis - 1878 to 1954 - 5 flood events (3 in the spring)
- Maple Leaf Drive Area - April 5, 1951 - 1 flood event (in spring)
- Tributary - March 12, 1959 - 1 flood event (in spring)

Total Number of Documented Flood Events7
Notable Road and Bridge Destruction Events2
- Near Mt. Dennis, September 13, 1878, "railroad bridge and bridge on Weston Road destroyed"
- Near Mt. Dennis, May 14, 1893, "bridges destroyed"

Don River
- Lower Don - 1804 to 1954 - 19 flood events (15 in the spring)
- Riverdale Flats - 1804 to 1970 - 19 flood events (15 in the spring)
- Mills Taylor Family - 1850 to 1902 - 5 flood events (4 in spring)
- Mills on Lower East Branch - 1850 to 1902 - 5 flood events (4 in spring)
- Sheppard Avenue Bridge - October 15-16, 1954 - 1 flood event
- Cummer Avenue Bridge - February 11, 1965 - 1 flood event (in spring)
- Gristmills - 1850 to 1881 - 4 flood events (3 in the spring)
- Thornhill - 1850 to 1975 - 11 flood events (9 in the spring) - 11 listed, report cites 12
- Mills and Small Dams, 1850 to 1881, 4 flood events (3 in the spring)
- Yonge Street at Highway 7, 1943 to 1975, 5 flood events (4 in the spring)
- Highway 7 Bridge, 1943 and 1950, 2 flood events (in the spring)
- Gristmill, Hosiel, 1835 to 1881, 5 flood events (4 in the spring)
- Bayview Avenue Bridge, 1850 to 1954, 4 flood events (2 in the spring)
- Hogg's Hollow, 1850 to 1954, 6 flood events (4 in the spring)
- Gristmill, Boyle, 1850 to 1881, 4 flood events (3 in the spring)
- Bathurst Street Bridge, October 15-16, 1954 - 1 flood event
- Mills on West Branch, 1850 to 1881, 4 flood events (3 in the spring)
- Highway 7 Bridge, 1943 to 1975, 4 flood events (3 in the spring)
- CNR Bridge Near Concord, 1878 to 1954, 3 flood events (1 in the spring)
- Small Dam, Lamer, 1850 to 1881, 4 flood events (3 in the spring)

Total Number of Documented Flood Events 111
Notable Road and Bridge Destruction Events13
- Lower Don, April 5, 1850, "Queen Street bridge destroyed, as well as Kingston Road bridge"
- Lower Don, September 13, 1878, "bridges destroyed at Gerrard Street, Queen Street, Kingston Road, as well as many smaller ones"
- Lower Don, February 28, 1902, "roads washed out"
- Sheppard Avenue Bridge (Sheppard Avenue and Leslie) , October 15-16, 1954, "Destroyed during Hurricane Hazel"
- Thornhill, April 5, 1850, "100 feet of Yonge Street washed out"
- Thornhill, spring 1943, "Yonge street washed out in several places"
- Bayview Avenue Bridge, April 5, 1850, "destroyed"
- Bayview Avenue Bridge, September 13, 1878, "destroyed"
- Bayview Avenue Bridge, October 15-16, 1954, "destroyed"
- Hogg's Hollow, April 5, 1850, "approaches to Yonge Street bridge washed out, bridge isolated"
- Hogg's Hollow, October 15-16, 1954, "Yonge Street bridge washed out"
- Bathurst Street Bridge, October 15-16, 1954, "Destroyed"
- CNR Bridge Near Concord, September 13, 1878, March 10-11, 1936, and  October 15-16, 1954, "The railroad was washed out"

Highland Creek
- Cottages and Highland Creek Drive, 1936 to 1977, 24 flood events (20 in the spring)
- Gristmill, Helliwell, 1869 to 1878, 2 flood events (1 in the spring)
- Highway 2 or Kingston Road Bridge, 14 flood events (12 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)
- Cottages at "The Willows", 16 flood events (14 in the spring)
- Scarborough Golf and Country Club, 1950 to 1977, 19 flood events (16 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)
- Military Trail Bridge, 1948 to 1977, 19 flood events (15 in the spring)
- Sawmill, 1869 to 1878, 2 flood events (1 in the spring)

Total Number of Documented Flood Events100
Notable Road and Bridge Destruction Events4
- Cottages at "The Willows", February 15, 1949, "roads washed out"
- Cottages at "The Willows", July 4, 1951, "roads washed out"
- Cottages at "The Willows", October 15-16, 1954, "roads, bridge near present Lawrence Avenue washed out"
- Military Trail Bridge,  August 27-28, 1956, "bridge destroyed"

Rouge River
- CNR Bridge, April 10, 1973, 1 flood event in spring
- Highway 2 of Kingston Road Bridge, 1878 to 1956, 5 flood events (3 in the spring)
- Caper Valley Ski Hill, February 2-3, 1978 , 1 flood event in spring
- Meadowvale Avenue Bridge, October 15-16, 1954, 1 flood event
- Mills, 1878 to 1929, 3 flood events (2 in the spring)
- CPR Bridge, October 15-16, 1954, 1 flood event
- Mills below Markham, 1878 to 1929, 3 flood events (2 in the spring)
- Markham, 1837 to 1973, 7 flood events (4 in the spring)
- Unionville, 1878 to 1973, 6 flood events (3 in the spring)
- Mills and Dams, 1878 to 1929, 3 flood events (2 in the spring)
- CNR Tracks, July 19, 1944, 1 flood event
- Mills, 1878 to 1929, 3 flood events (2 in the spring)
- Rouge Valley Inn, October 15-16, 1954, 1 flood event
- Mills on the Little Rouge, 1878 to 1929, 3 flood events (2 in the spring)
- Con.9 Markham Township, 2 flood events (2 in the spring)
- CNR Bridge, 1947 to 1954, 2 flood events
- Mills and Small Dams, 1878 to 1927, 3 flood events (1 in the spring)

Total Number of Documented Flood Events46
Notable Road and Bridge Destruction Events6
- Markham, May 16, 1937, "bridge washed-out (on present Hwy. 7)"
- Markham, October 15-16, 1954, 'town "marooned" by Hwy. 7 washouts on both east and west sides'
- Unionville, October 15-16, 1954, "Main Street washed out north of Hwy. 7"
- CNR Tracks, July 19, 1944, "The tracks were washed out"
- CNR Bridge, August 18, 1947, "Washed out"
- CNR Bridge, October 15-16, 1954, "Washed out" "passenger train partially derailed"

Duffin Creek
- Gristmill, 1878 to 1919, 3 flood events (1 in the spring)
- Pickering Village and Cottages on Riverside Drive, 27 floods (24 in the spring)
- Mills on West Branch, 1878 to 1890, 2 flood events
- Whitevale, 1878 to 1950, 5 events (3 in the spring)
- Green River, 1878 to 1954, 6 events (3 in the spring)
- Mills between Stouffville and Green River, 1878 to 1919, 3 flood events (1 in the spring)
- Stouffville, 1878 to 1972, 10 flood events, (7 in the spring)
- Mills and Small Dams, 1878 to 1919, 3 flood events (1 in the spring)
- Greenwood, 1878 to 1956, 7 flood events (4 in the spring)
- Mills on East Branch, 1878 to 1919, 3 flood events (1 in the spring)

Total Number of Documented Flood Events = 69

Grand Totals:
Total Number of Documented Flood Events = 479
Notable Road and Bridge Destruction Events31

So yes, we have always had many floods in the past and many road, bridge and rail washouts too. And urban areas have expanded considerably since 1804, meaning more places to experience high rainfall and more runoff (before we started to practice better stormwater management quantity control). While the loss of Finch Avenue during the August 19, 2005 storm was significant, we have not had any major road or bridge washouts since, only Military Trail Bridge, August 27-28, 1956 which it is noted "has not been redesigned and remains low and vulnerable to flooding". So despite high runoff stresses and more and more crossings, the loss of roads and railways has not been an issue. This suggests that today's floodplain management and hydraulic structure (i.e., bridge and culvert) practices are largely effective as well, resulting in overall resilient infrastructure.

The TRCA flood history report notes wet cellars or basements for only a couple of the nearly 400 events. That is in contrast with today when it is basement flood damages that are driving flood losses in southern Ontario, not riverine flooding.

***

Interesting comment on land use planning practices:
- in Hogg's Hollow, "All of the houses flooded during Hurricane Hazel remain in the floodplain, and several more have been built" ... obviously this just adds to old risk
- in The Willows, "The cottages at The Willows which survived Hurricane Hazel were removed shortly afterwards, and the valley is now parkland" ... and this is the best way to remove risk in the highest risk zones