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: