Toronto Island Flooding 2017 - Were Lake Ontario Levels Extreme? No, Barely Above Historical Maximum Levels

Blockbuster Release: Toronto Island Flood 2017..
really just a sequel to 1947, 1973, 1952 lake levels ...
and to storms back in the 1800's too (note - original
record years corrected Feb. 2019)
See 2019 update at bottom of the post

It is easy to 'think fast' and make observations about hydrologic and hydraulic events without looking at objective data. For example the document Blueprints for Action Minimizing Homeowner Flood Risk in the GTHA July 2017 notes the Toronto Island flooding:

"For many Torontonians in general, 2017 could be called “the year of the flood.” Higher amounts of rainfall during the spring caused Lake Ontario to swell by 55 centimetres, submerging not only parts of the Toronto Islands, but also affecting regional shorelines..."

And concludes:

"The cause of these kinds of flooding isn’t a secret. Climate change is having major local impacts across the Greater Toronto and Hamilton Area (GHTA) including major flooding. Storms and extreme weather that typically happened every 20, 40, 80, to 100 years are now happening with increasing frequency."

What does data show us, however? Are Lake Ontario levels impacted in a major way by climate change? Not really. Below is a review of May to August Lake Ontario levels showing previous levels back to 1918:

Lake Ontario Historical Levels 2017 Flood Toronto Island
Correction: August 2017 did not set a record - that is held by 1947 levels. April record remains 1973.

May 2017 Lake Ontario levels were a few centimetres above historical maximum values in 1973 - June levels in 2017 (not shown) were similarly only a few centimetres above previous maximum monthly average values.

We broke a previous 1952 record by a couple inches in June according to Environment and Climate Change Canada's LevelNews;

"“Lake Ontario’s level at the start of June … set a new record for the highest beginning-of-June level on Lake Ontario in the period of record (1918 to present) breaking the previous record set in June 1952 by 5 cm.”

By August 2017 Lake Ontario levels were no greater than previous maximum values in 1947. So 2017 Lake Ontario levels are not a blockbuster climate change impact but rather a slow prodding sequel to previous fluctuations in levels.

So what is different in 2017 compared to previous years with high water levels? Is the risk of flooding on Toronto Island greater today than before? Yes, and this has to do with land use planning and risk management as opposed to climate change risks. This is a short chronology of development on the Toronto Islands:
  • 1858 – Storm separates Toronto Islands from the mainland. Quinn's Hotel and Parkinson's Hotel are destroyed.
  • 1950’s – 630 Cottages / Homes on Toronto Islands
  • 1970’s – 250 Cottages / Homes , by 1978 Metro Toronto had writs of possession for these homes and planned removal
  • 1981 - Province of Ontario passed a law legalizing the Islanders to stay until  2005
  • 1993 - Ontario Government passed Toronto Islands Residential Community Stewardship Act, Islanders to purchase 99-year land leases from a Land Trust
Was granting 99-year leases a good land use planning idea considering storm and flooding risks? Or did it unnecessarily add flood risk to a known high risk area, that had high lake levels in the past and significant storm damages even back in the mid 1800's? Obviously history shows us that there is not a significant climate change impact affecting flood risk but rather deliberate land use planning increasing the investment in a vulnerable area, as opposed to removing the risk (as was the plan through the 1970s).

And on the conclusion that storms and extreme weather are happening with greater frequency? Not at all. As Environment and Climate Change Canada has corrected the insurance industry on several occasions including recently in Canadian Underwriters:

"Associate Editor’s Note: In the 2012 report Telling the Weather Story, commissioned to the Institute for Catastrophic Loss Reduction by the Insurance Bureau of Canada, Professor Gordon McBean writes: “Weather events that used to happen once every 40 years are now happening once every six years in some regions in the country.” A footnote cites “Environment Canada: Intensity-Duration-Frequency Tables and Graphs.” However, a spokesperson for Environment and Climate Change Canada told Canadian Underwriter that ECCC’s studies “have not shown evidence to support” this statement."

The Toronto Island flooding is not unlike the Gatineau flooding in 2017. Buildings have been historically been built in areas that are at a high risk of flooding, and given enough time the risk will manifest themselves. Over time, old records will be broken - that is fundamental of statistical observations of random events, and not necessarily climate change impacts pushing old records higher. And the Toronto Island risks are not unlike high profile locations like High River, Alberta in 2013 or low profile locations like Cedar Beach Road, Clarington, Ontario in 2017. All these locations have intrinsic flood vulnerabilities based on their location and land use planning decisions. It is easy to call this a climate change impact but it it not accurate as the risks are long-standing ... yes back to the 1800's there were storm risks too.

Here is a summary of historical water levels (per August 2017 Bulletin and June 2017 LevelNews) and land use planning decisions at Toronto Islands (per Wikipedia):

Lake Ontario water levels 2017 Toronto Island flood risk lease agreements
Historical Lake Ontario water elevations and 2017 records.
Responsible journalism should not make sensational headlines out of every flood event that occurs and recognize that there is not a 'new normal' in weather extremes but rather the 'old normal' showing up again in a sequel. For example:

1) GO Train Flooding - Not New:
GO Train Flood Toronto
2) Toronto Road and Basement Flooding - Not New:Toronto Flood History

3) Toronto Island flooding and high Lake Ontario levels - not new either.

2017 levels nudged above previous records for May 1973, June 1952 and July 1947. It is not reasonable to expect that after 70 years very old records may be surpassed, like the July 1947 record being surpassed in 2017? Or that newer records would be surpassed too, like May 1973 after 44 years? After all its only a 100 year period of data and the Cornwall and Long Sault dams have been in place for just over half that time.


In 2019, levels have approached previous maximum levels and in June are expected to exceed previous monthly average levels by several centimetres. This chart shows May 2019 levels that are not above the 2017 maximum average monthly level - 2017 was 7 centimetres above the previous maximum in 1973.

The projected June 2019 average monthly level is expected to be 5 centimetres above the 2017 maximum. The 2017 maximum was 5 centimetres above the previous 1952 maximum.

So the records have been "nudged" higher in 2017 (May record) and in 2019 (projected June record).

How can one adjust to such water level fluctuations? Retreating from the known hazard is one approach. PARA stands for "Protect, Accommodate, Retreat or Avoid" and is discussed in the Canadian context in the paper Protect, accommodate, retreat or avoid (PARA): Canadian community options for flood disaster risk reduction and flood resilience by University of Waterloo researchers. In the paper it is noted that "In Toronto, post-Hurricane Hazel, the City used retreat as an effective strategy to reclaim and rezone flood-prone land." and that in the five years after the storm at least 530 properties were expropriated and over 9000 hectares of land rezoned to disallow housing.

In some cases iconic buildings like the Leuty Avenue Lifeguard Station in Toronto's eastern Beaches neighbourhood have been moved to accommodate changing water levels. The station has recently been raised to protect it from recent high lake levels and has been relocated 4 times since its construction in 1920:

Less Extreme Ontario Rainfall - Precipitation Intensities For Design of Buried Municipal Stormwater Systems by Yi Wang. A Thesis presented to The University of Guelph

Those with decreasing rainfall intensities
could be Singing in the Rain, with lower
stresses on their buried municipal
infrastructure systems.

Wang's Ph.D. thesis at the University of Guelph describes changes in frequent and extreme rainfall trends. The thesis is available here. Confidence limits on 2-year, 5-year, 10-year and 25-year rainfall intensities for durations of 5 minutes to 2 hours show no significant changes in most cases and decreasing rainfall intensities at many stations.

Results from page 51 show that there are more than twice as many decreases in rainfall as increases considering the 90% confidence limit, as shown below:

Table 3.2: Results of 90% Confidence Interval Comparison Test

ID     5min 10min 15min 30min 1h  2h
6034075 ---- ---- ---- ---- ---- ----   Kenora A
6037775 ---- ---- ---- ---- ---- ---   Sioux Lookout A
6057592 ---- ---- ---- ---- ---- ----   Sault Ste Marie A
6085700 ---- ---- ---- ---- ---- ----   North Bay A
6100971 ---- ---- ---- ---- ---- ----   Brockville PCC
6104175 ---- ---- ---- ---- ---- ----   Kingston Pumping Station
6105978 ---- ---- ---- ---- ---- ----   Ottawa CDA RCS
6116132 ---- ---- ---- ---- ---- ----   Owen Sound MOE
6131415 ---- ---- ---- --↓↓ --↓↓ ----   Chatham WPCP
6131983  /    /   ---- -↑↑↑ --- ----   Delhi CS
6136606 ---- ---- ---- ---- ---- ----   Port Colborne
6137362 -↓↓↓ ---- ---- ---- ---- ----   St Thomas WPCP
6139525 ↓↓↓↓  /   ↓↓↓↓ ↓↓-- --- ----   Windsor A
6142400 ---- ---- ---- ---- ---- ----   Fergus Shand Dam
6144478 ---- ---- ---- ---- ---- ----   London CS
6148105 ---- ---- ---- ---- ---- ----   Stratford MOE
6150689 ---- --- ↑↑-- ---- ↑↑-- ---   Belleville
6153301  /   ---- ---- ---- ---- ----   Hamilton RBG CS
6158355 -↓↓↓ -↓↓↓ ---- ---- ---- ----   Toronto City
6158733  /   ----  /    /    /    /     Toronto Intl A
6158875 ---- ---- ---- ---- ---- ----   Trenton A

·        The arrows and hyphens in cells represent the results of CI comparison of 2, 5, 10, and 25-year events (from left to right). An up-arrow indicates an increase of rainfall intensity occurred in the 2nd period of record, and a down-arrow  indicates a decrease of rainfall intensity. A hyphen means no significant change (α = 0.1) is shown or, in other words, the CIs are not significantly different. Cells with slashes represent records that are not stationary.

11 significant increases , 24 significant decreases
Southwestern to Central Ontario most significant decreases

Results from page 52 show that there are almost twice as many decreases as increases considering the 80% confidence limit, as shown below:

Table 3.3: Results of 80% Confidence Interval Comparison Test

ID    5min 10min 15min 30min 1h  2h
6034075 ---- ---- ---- ---- ---- ----   Kenora A
6037775 ---- ---- ---- ---- --- ↑↑--   Sioux Lookout A
6057592 --- ---- ---- ---- ---- ----   Sault Ste Marie A
6085700 ---- ---- ---- ---- ---- ----   North Bay A
6100971 ---- ---- ---- ---- ---- ----   Brockville PCC
6104175 ---- ---- ---- ---- ---- ----   Kingston Pumping Station
6105978 ---- ---- ---- --- --- ----   Ottawa CDA RCS
6116132 ---- ---- ---- ---- ---- ----   Owen Sound MOE
6131415 ---- ---- ---- -↓↓↓ --↓↓ ----   Chatham WPCP  
6131983  /   ---- --- -↑↑↑ -↑↑↑ ----   Delhi CS
6136606 ---- ---- ---- ---- ---- ----   Port Colborne 
6137362 -↓↓↓ --- ---- ---- ---- ----   St Thomas WPCP
6139525 ↓↓↓↓  /   ↓↓↓↓ ↓↓↓↓ --- ---   Windsor A
6142400 ---- ---- ---- ---- ---- ----   Fergus Shand Dam    
6144478 ---- ---- ---- --- ---- ----   London CS
6148105 ---- ---- ---- ---- ---- ----   Stratford MOE
6150689 ↑↑-- ↑↑-- ↑↑↑- --- ↑↑—  ↑↑↑↑   Belleville    
6153301  /    /   ---- --- -↓↓↓ ----   Hamilton RBG CS
6158355 ↓↓↓↓ -↓↓↓ -↓↓↓ ---- ---- ----   Toronto City
6158733  /   ----  /    /    /    /     Toronto Intl A
6158875 ---- ---- ---- ---- ---- ----   Trenton A

·        The arrows and hyphens in cells represent the results of CI comparison of 2, 5, 10, and 25-year events (from left to right). An up-arrow indicates an increase of rainfall intensity occurred in the 2nd period of record, and a down-arrow  indicates a decrease of rainfall intensity. A hyphen means no significant change (α = 0.1) is shown or, in other words, the CIs are not significantly different. Cells with slashes represent records that are not stationary.

24 significant increases , 41 significant decreases
Southwestern to Central Ontario most significant decreases


Ontario climate change extreme rainfallHere are Wang's tables in original graphic format:

Ontario climate change rainfall

Climate-driven variability in the occurrence of major floods across North America and Europe - Journal of Hydrology Review

An assessment of major flood trends was conducted by a group of researchers including Environment and Climate Change Canada and University of Waterloo Civil and Environmental Engineering. They found no evidence that climate change has to date increased the occurrence of floods.

Concern over the potential impact of anthropogenic climate change on flooding has led to a proliferation of studies examining past flood trends. Many studies have analysed annual-maximum flow trends but few have quantified changes in major (25–100 year return period) floods, i.e. those that have the greatest societal impacts. Existing major-flood studies used a limited number of very large catchments affected to varying degrees by alterations such as reservoirs and urbanisation. In the current study, trends in major-flood occurrence from 1961 to 2010 and from 1931 to 2010 were assessed using a very large dataset (>1200 gauges) of diverse catchments from North America and Europe; only minimally altered catchments were used, to focus on climate-driven changes rather than changes due to catchment alterations. Trend testing of major floods was based on counting the number of exceedances of a given flood threshold within a group of gauges. Evidence for significant trends varied between groups of gauges that were defined by catchment size, location, climate, flood threshold and period of record, indicating that generalizations about flood trends across large domains or a diversity of catchment types are ungrounded. Overall, the number of significant trends in major-flood occurrence across North America and Europe was approximately the number expected due to chance alone. Changes over time in the occurrence of major floods were dominated by multidecadal variability rather than by long-term trends. There were more than three times as many significant relationships between major-flood occurrence and the Atlantic Multidecadal Oscillation than significant long-term trends."

The paper is available from the Journal of Hydrology. The authors are from across the world.

Glenn A.HodgkinsaPaul H.WhitfieldbDonald H.BurncJamieHannaforddBenjaminRenardeKerstinStahlfAnne K.FleiggHenrikMadsenhLuisMedieroiJohannaKorhonenjConorMurphykDonnaWilsong
U.S. Geological Survey, 196 Whitten Road, Augusta, ME 04330, United States
Environment and Climate Change Canada, 401 Burrard Street, Vancouver, BC V6C 3S5, Canada
University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada
Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Wallingford, Oxfordshire OX10 8BB, United Kingdom
Irstea Lyon, Hydrology-Hydraulics, 5 rue de la Doua BP32108, 69616 Villeurbanne cedex, France
Albert-Ludwigs-Universität Freiburg, Fahnenbergplatz, 79098 Freiburg, Germany
Norwegian Water Resources and Energy Directorate, P.O. Box 5091, Majorstua, 0301 Oslo, Norway
DHI, Agern Allé 5, DK-2970 Hørsholm, Denmark
Technical University of Madrid, ETSI Caminos, Canales y Puertos, c/ Profesor Aranguren, 3 28040 Madrid, Spain
Finnish Environment Institute, SYKE, Freshwater Centre, P.O. Box 140, 00251 Helsinki, Finland
Irish Climate Analysis and Research UnitS (ICARUS), Department of Geography, Maynooth University, Maynooth, Co. Kildare, Ireland

Since rainfall intensities are not increasing dramatically across Canada, as demonstrated by Environment and Climate Change Canada (ECCC) in the Atmosphere-Ocean in 2014, saying rainfall intensities are stationary, it makes sense that major floods are not increasing either. Of course there may be local regional trends - ECCC found that there are decreasing rainfall intensities in regions such as the St Lawrence basin of southern Quebec and the Maritimes. Their Engineering Climate Datasets (version 2.3) also show twice as many statistically significant decreasing trends as increasing ones in southern Ontario.

The paper Climate-driven variability in the occurrence of major floods across North America and Europe focused on minimally altered catchments in order to isolate climatic as opposed to hydrologic drivers. It focused on large watersheds. As noted on this blog, urbanization is a key driver of flood risk in small urban catchments and is expected to have increased of the past  50-100 years in many Ontario cities. This is link to GIS mapping of changes: Ontario city urbanization affecting runoff and flood risk since from 1966 to 2000.

If Hurricane Harvey hits Toronto will it be "The Day After Tomorrow" Stormageddon, Rainpocalypse? Sensational pseudo-science in media should be viewed with caution.

hurricane harvey torontoThe comment below is awaiting moderation on The Weather Network. It is in response to the article "Visualizing what Harvey's impacts would look like in Canada".


Toronto overland flooding NewtonbrookThe Weather Network broadcasts a segment on the movie The Day After Tomorrow calling it a silly, non-scientific tale and discounting the sensational stormageddons portrayed in the movie. This article is just similar sensationalization, and I caution even calling it 'pseudo-science' because there are too many gaps in basic hydraulics and hydrology to make the weather-flood math even worth dissecting. A couple cool graphics, but no science in the article. An alternative? Yes, it is possible to analyze the impact of storms on cities using urban hydrology and hydraulics to estimate where water could spread - I have assessed Toronto for the 100-year storm spread and multiples of that spread that could represent how a mega-storm could affect the city, street by street: 
Toronto urban flooding overland flow May 2000 August 2005 July 2013 flood report 
Toronto urban flooding Beaches East York Leaside
The interactive map at the link above can be used to explore your street's risk in Toronto (realistic storms, not sensational 'stormageddons'. I have done similar analysis for southern Ontario that uses complete elevation models of Ontario, considers rainfall statistics, applies hydrologic runoff principles and hydraulic flow principles: 

A few 2D maps on hot spots and 3D renderings are attached. 

The Weather Network promotes Science Behind the Weather all the time but does not get into much depth on hydrology and hydraulics and other scientific disciplines that come into play between weather and flooding. 


And a follow-up comment:

Just checking the "math" on Toronto Hurricane Harvey flooding simulation. I give it an "A" in grade 9 Algebra - yes, 56.8 cubic kilometres of water will have a height of 90 metres over Toronto's 630 square kilometers - kudos for being able to divide a volume by an area to get a depth - that would just about immerse the 130 metre tall Royal York Hotel as shown. But a D minus in Geography - grade 9 kids learn about the water cycle and that rain runoff water flows off land - it does not stack up like jello unsupported from its sides like the Hurricane Harvey Toronto flood math suggests. A F in physics because runoff water is viscous and flows instead of ponding up vertically. E minus in hydrology for anyone with an engineering college technologist certificate - again, water accumulates over and runs off through watersheds not defined by municipal boundaries - the rainfall volume should actually be bigger than 56.8 because the Toronto watersheds extend beyond the political boundaries. D minus for hydraulics as when it rains runoff flows away based on the hydraulics and at times the storage routing of the urban drainage and river and lake systems. This means runoff does not stack vertically, some infiltrates into the ground for small storms, and most flows away during the storm with the flood depth determined by the hydraulics at the time of peak outflow. All 2nd year civil engineers know from basic hydrology courses that axiom. But in the Hurricane Harvey simulation it is not even a remote consideration, nor is basic watershed science and hydrologic cycle considerations. I really do encourage The Weather Network to focus on the science behind flooding and it requires a more broad perspective on scientific disciplines beyond meteorology. 


Below is a critique of the science of The Day After Tomorrow on Wikipedia. The Hurricane Harvey Toronto flooding simulation is also an impossible joke as well - a cheap thrill ride for the weak minded: 

Some scientists criticized the film's scientific aspects. Paleoclimatologist and professor of earth and planetary science at Harvard University Daniel P. Schrag said, "On the one hand, I'm glad that there's a big-budget movie about something as critical as climate change. On the other, I'm concerned that people will see these over-the-top effects and think the whole thing is a joke ... We are indeed experimenting with the Earth in a way that hasn't been done for millions of years. But you're not going to see another ice age – at least not like that." J. Marshall Shepherd, a research meteorologist at the NASA Goddard Space Flight Center, expressed a similar sentiment: "I'm heartened that there's a movie addressing real climate issues. But as for the science of the movie, I'd give it a D minus or an F. And I'd be concerned if the movie was made to advance a political agenda." According to University of Victoria climatologist Andrew Weaver, "It's The Towering Inferno of climate science movies, but I'm not losing any sleep over a new ice age, because it's impossible."

Patrick J. Michaels, a former research professor of environmental science at the University of Virginia who rejects the scientific consensus on global warming, called the film "propaganda" in a USA Today editorial: "As a scientist, I bristle when lies dressed up as 'science' are used to influence political discourse."College instructor and retired NASA Office of Inspector General senior special agent Joseph Gutheinz called The Day After Tomorrow "a cheap thrill ride, which many weak-minded people will jump on and stay on for the rest of their lives" in a Space Daily editorial.