University of Guelph Research Shows Lower Spring Flooding With Global Warming, No Change in Rainfall, and Explains Urban Flooding Due to Urbanization - Not Climate Change Effects

Research from the University of Guelph has shown that climate change has reduced spring flooding risk (exponential growth in frost-free days with more recharge and less snow pack / spring melt) and that summer flow changes are due to urbanization, not changes in precipitation.

The presentation below summarizes the research and is entitled "Disentangling Impacts of Climate & Land Use Change on Quantity & Quality of River Flows in Southern Ontario" - the authors, Trevor Dickinson and Ramesh Rudra from the University of Guelph clearly see the need to clarify drivers for flow changes and to avoid the common media mistake of associating all extreme hydrologic conditions with climate change and omitting changes that may lower risks (like spring flooding in some watersheds).

Disentangling Impacts of Climate & Land Use Change on Quantity & Quality of River Flows in Southern Ontario Trevor Dickinson Ramesh Rudra University of Guelph from Robert Muir

Research indicates:
1) Monthly and Annual Precipitation has remained unchanged (see slide 7)
2) Temperatures have risen 'mostly in the winter' (see slide 13 - 14), meaning summer maximum temperatures that are typically associated with extreme rainfall have not increased, or have decreased
3) Extreme daily maximum temperatures have decreased (slide 14)
4) Increased winter temperatures mean more steady winter runoff, more infiltration and "Decreased Snowmelt Floods" (see slides 24 - 31)
5) Urbanization increases runoff coefficients (slide 36-37) and:

" So … in Ontario urban watersheds: - urban development has augmented the winter and spring climate change impacts; and - summer flow volumes have increased dramatically, in volume and frequency, these impacts being completely due to urban development."

The big take away is that urbanization is a key driver for summer river flows in Southern Ontario, but climate change is not - this is supported by trends in the Engineering Climate Datasets (version 2.3) that show twice as many statistically significant decreasing Southern Ontario trends as increasing ones.

This analysis is consistent with review by others showing change in minimum temperatures but no change in summer maximum temperatures. For example, the Ontario Centre for Climate Impacts and Adaptation Resources reviewed climate change trends for several stations - for Ottawa airport, between 1939 and 2014, the average winter minimum is up by 2.5 degrees Celcius and average winter mean is up 2.2 degrees. But the summer maximum is flat - no change. While the summer mean temperature is up by 0.5 degrees, this is due to increases in minimum temperatures, which were up by 1.1 degrees. These graphs from the Centre show the difference in winter temperatures changes and summer temperatures changes:

Winter temperatures have increased with climate change - Ottawa, 1939-2016

Summer maximum temperatures (middle chart) have NOT increased with climate change - Ottawa, 1939-2016. Changes in mean temperature are driven by changes in minimum temperatures.

Those who point to the Clausius-Clapeyron equation and a greater water vapour holding capacity at higher temperatures as a driver for climate change-induced flooding in urban areas should reevaluate their position, and consider the data on maximum temperatures. Since there is no increase in summer maximum temperature at some stations, the cause of flooding due to extreme rainfall cannot be greater water vapour holding capacity of the air - as research at the University of Guelph has shown, urbanization and not climate change is the key driver for changes in river flow. We can expect the same types of flow impacts beyond river systems and within municipal infrastructure systems, where urbanization and intensification have increases hydrologic stresses on systems even with no change to rainfall inputs.

The Ontario Centre for Climate Impacts and Adaptation Resources reviewed climate change trends for Hamilton as well. The following charts show the same relative temperatures changes as Ottawa:

Hamilton winter temperature has increased the most due to climate change.

Hamilton summer temperatures have increased at only a fraction of the winter increase.

 The Hamilton summer maximum temperatures increase (0.4 degrees in 40 years from 1970 to 2010) is only a fraction of the winter maximum increase (1.8 degrees in 40 years). The 0.4 degree increase in summer maximum would translate into less than a 3% change in water vapour holding capacity over 40 years. A review of research in another post has shown that temperature increases have not resulted in extreme rainfall increases across Canada - see post here.

Urbanization has increased significantly in Southern Ontario since the mid 1960's as shown in this post - this includes Hamilton growth:



In the Toronto area, where the University of Guelph assessed changes in runoff and linked these to urbanization as opposed to climate change, growth has also been significant since the mid 1960's. The following table shows changes in Toronto-area watersheds where urbanization increased from 59% to 986% over a perido of about 35 years. Compared to theoretical temperature-induced water vapour changes changes of a few percentage, if any at all, urbanization clearly explains higher runoff stress and flood risk while climate change explains none of the risks.

Does Higher Temperature Increase Rain Intensity? Not Always, Observations Show Decreasing Rain Intensity. Southern Ontario Twice As Many Statistically Significant Decreases In Annual Maximum Rainfall.

One degree temperature rise increases water vapour holding capacity
by 7%, but does it increase rainfall intensity?

High school science teachers and media have been saying that temperature increases associated with climate change cause a direct increase in water vapour and therefore, by association, more extreme rainfall.  This has been reported for years, like here in the Guardian where they say "A warmer atmosphere can hold more moisture, and globally water vapour increases by 7% for every degree centigrade of warming."

The Clausius-Clapeyron (C-C)
equation describes the water-holding capacity of the atmosphere as a function of temperature.

Geophysical Research Letters research looks at historical data to see if this theory linking temperature and rain intensity can be verified and what other explanatory variables are available. Researches from Lamont-Doherty Earth Observatory, Columbia University, MIT, and Institute Centre for Water Advanced Technology and Environmental Research (iWater), Masdar Institute of Science and Technology, and Department of Chemical and Environmental Engineering, Masdar Institute of Science and Technology analyzed how extreme rainfall intensities in the USA depend on temperature (T), dew point temperature (Td), and convective available potential energy (CAPE). The analysis considers geographic sub-region, season, and averaging duration.

What did researchers find in the data?:

"When using data for the entire year, rainfall intensity has a quasi Clausius-Clapeyron (CC) dependence on T, with super-CC slope in a limited temperature range and a maximum around 25°C

So Clausius-Clapeyron is only quasi-valid, meaning there is not a strong relationship between rain intensity and temperature. And rain intensities peak at 25 degrees Celcius ... they do not keep going up with temperature increases. The Guardian missed these details. Who else made the temperature-water vapour-rainfall relationship claim:

The magazine Science article How Much More Rain Will Global Warming Bring? touches on the 1 degree - 7 % atmospheric vapour relationship back in 2007. Bloggers around the world repeat this, and even David Suzuki is saying it. But lets look at more the the research findings based on actual data in Geophysical Research Letters. These charts show how rain intensities do not increase at the CC rate above 22 degrees:

The fourth column of charts shows temperature T on the x-axis. On the y-axis is slope of the relationship between rain intensity and temperature. The dashed red line is the predicted CC rate, meaning above 22 degrees rain increases less that predicted by CC. So no, this theory does not hold water (pun intended). In fact for some of the highest temperatures for some quantiles in the North Central and South, slope is negative, meaning that increased temperature DECREASES rainfall intensity (black lines go below zero).

Looking at the third column of charts with LnP on the y-axis, we see that for several quantiles of precipitation in both winter and summer, LnP does not reach the predicted rate at all (coloured lines below the predicted rates shown in the black dashed lines). In plain english this means the predicted increase in rain intensity with temperature is never met for small storms, e.g., the ones responsible for erosion, etc. So the theory is flawed for small storms.

In the summer, i.e., black lines in third column, precipitation as LnP flattens out or sometimes decreases at the highest temperatures, mostly in the South and Central of the US - for the lower 2 to 3 quantiles the CC rate is not met or just met. In the North, rain intensity for the lower quantiles of precipitation flattens out and decreases above 25 degree Celcius.

The take-away is that simple relationships make great theories. Real systems are more complicated than the Clausius-Clapeyron (CC) would suggest.

Lets look at something simpler in Ontario, Canada. Temperatures have increased. At right are temperature trends plotted by Statistics Canada. There is an increase from the late 1940's to 2008. Pretty clear.

Below are maximum annual observed rainfall trends for Toronto's long term climate station from Environment and Climate Change Canada's Engineering Climate Dataset Version 2.3, from the 1940's to 2007. It shows decreasing annual maximum rainfall for all rainfall durations from 5 minutes to 24 hours. Obviously the real world data shows us that despite increasing temperature, there is no corresponding increase in maximum observed rainfall.

The hypothesis that rising temperatures result in higher water vapour and then also more extreme rainfall is rejected based on the observations in southern Ontario. While temperatures are up in Ontario, there are twice as many statistically significant decreasing annual maximum rainfall trends as increasing ones as summarized from the Engineering Climate Dataset (version 2.3):

More statistically significant DECREASES in rainfall intensity are observed than increases.

For short duration rainfall, the convective storms that cause flash flooding in urban areas, we can look at the duration of 2 hours or less - there is just one statistically significant increase in annual maximum rainfall, and 6 examples of statistically significant decreasing rainfall maximum.

Evidence-based policies for flood mitigation and other stormwater or water resources management activities first require accurate characterization of factors affecting runoff and flow conveyance in municipal and natural drainage systems. By hypothesizing that rainfall intensities are increasing as a result of higher temperatures, flood damage mitigation could be achieved by combating green-house gas emissions to stall temperature increases. Data shows that extreme rainfall is not increasing with temperatures, and therefore an increase in flood damages is due to other factors (e.g., hydrology, hydraulics) - as a result effective flood damage mitigation must focus on key drivers and not temperature or rainfall trends.

We cannot explain severe weather, extreme rainfall, tornados and hail in Ontario with simple relationships that have been shown to contradict observation data.

***

Canadian data analyzed by researchers at the University of Western also concluded that the Clausius-Clapeyron (C-C) equation did not match real temperature and rain data as observed in climate stations including Vancouver, Brandon, London and Moncton. As shown on the following graphs the real data relationships (coloured lines) do not follow the theoretical C-C scaling lines (dashed lines).

For Vancouver, precipitation decreases at higher temperatures (downward sloping solid lines).

For Brandon, London and Moncton, the slope of the precipitation-temperature trend line is less than the theoretical dashed line for most positive temperatures. In Moncton the trend is flat, meaning higher temperatures above 5 degrees C do not increase precipitation.

Key conclusions of the Western analysis were:

"Summary
- The sub-daily daily maximum precipitation shows weak linear correlation to the daily temperature for most stations and durations. Only lower durations for Moncton, London and Brandon show correlations roughly identical to the theoretical C-C 7% per 0C rate.
- For Vancouver station none of the sub-daily durations present linear correlation to temperature. For temperatures higher than 10 ºC negative slopes are observed.

Conclusion
- The Clausius-Clapeyron scaling rate clearly does not apply for any of the stations consider in this study, and should not be arbitrarily applied to derive IDF curves for future."

The analysis was presented at the ICLR Friday Forum in March 2017.

Researches also concluded that the use of Western's IDF_CC tool projections of future IDF would be preferred to any reliance on the C-C equation and its theoretical 1 degree = 7% scaling factor.

Environment Canada CO2 Climate Report Denies Link Between Extreme Weather and Climate Change

The report is available at this link. Yes it is dated (2002) and predates several extreme rainfall events in Southern Ontario and Alberta, but it is valuable in that it shows how unusual, extreme weather events and disasters - even more recent ones - should be evaluated to answer the question "Are recent unusual weather events and related impacts and disasters caused by natural variability or climate change?"

As stated in the report "The following provides an update on that analysis through a case-by-case discussion of various types of unusual weather events that have occurred in Canada and elsewhere over the past five years or so." It explores a range of topics:

• Temperature Related Events
• Unusual Annual and Seasonal Temperatures
• Mild Winters
• Summer Heat Waves
• Longer Growing Seasons
• Water Related Events
• Extreme drought
• Lake/River levels and flows
• River Flooding
• Coastal Flooding
• Storms
• Convective storms
• Winter storms
• Tropical storms
• Oceanic and Sea Ice Behaviour
• El Niño/La Niña
• Arctic sea ice
• Ecological and Social Infrastructures
• Permafrost decay
• Ecological impacts (including forest fires)
• Community Impacts
• Aggregate social costs of weather related disasters
• Environmental refugees/disasters

Its a long list and the assessment of events in each category need a separate review. Unfortunately its hard to get down this list before an internet ad "Once beautiful celebrities - look at them now!" diverts our attention. Its pretty easy to exercise our "anchoring  bias" and think about the first row 'temperature' and then lump all the other difference processes in the same boat and think "Yeah, they are all changing the same way like temperature is". More on our cognitive biases involving extreme weather is posted here. So kudos to Environment and Climate Change Canada (formerly Environment Canada) for encouraging the slow, conscious, effortful, complex yet reliable evaluation process needed to answer questions on extreme weather and climate change - also showing good scientific rigour, data sources are included for each evaluation.

Highlights:

River Flooding: "There is no evidence that the total number of extreme precipitation events has increased across all of Canada in recent decades. However, intense spring rainfall events have become more frequent in eastern Canada."

     and

"As with severe droughts, intense floods occur from time to time as part of natural climate variability,

and individual events cannot be directly attributed to global causes."

Storms: "There is no evidence to suggest that thunderstorms, hailstorms or lightning are occurring

more frequently."

     and

"However, a Canadian study of tornadoes in the Canadian Prairies indicate that these are now occurring earlier in the year, consistent with warmer spring temperatures. "

So what does Environment Canada say more recently about storm frequency? No change again. Last year in response to an insurance broker cbcnews.ca interview on increasing premiums and claims saying "A lot of it has to do with the frequency of the storms and I think you could even extrapolate that it's got to do with climate change," ..."we're getting 20 times more storms now than we were 20 years ago." Environment Canada offered this correction in late 2015 that cbcnews.ca has posted:

'Environment Canada says it has recently looked at the trends in heavy rainfall events and there were "no significant changes" '

This above statement saying no changes is related to Southern Ontario, but is not unlike other regional short term rainfall trends across Canada as noted by Environment Canada scientists in a 2014 journal article - their research still shows "no detectable trend signal", despite recent statements by the Insurance Bureau of Canada that would suggest otherwise.

In the CO2 / Climate Report, Environment Canada discusses predictions about future changes as well. Regarding storms they note "Other studies project that heavy summer rainfall events (>25 mm/day) over central North America may increase in intensity by about 150%. These have led IPCC to conclude that more intense rainfall is very likely over many areas, and that flood magnitude and frequency are likely to increase in most regions".

So can we check if the number of days with greater than 25 millimetres of rainfall is going up? Or is the opposite trend happening? This 25 mm frequency characteristic is also described in Toronto's Future Weather & Climate Driver Study by SENES in 2012 - but it says the number of those storms will go down, not up like IPCC says - a total contradiction. As noted in the SENES summary report, using a fine scaled climate model customized for Toronto, the "Number of Days with More Than 25mm", deemed Extreme Rainfall, would decrease from 16 days in 2000-2009 to only 9 days in 2040-2049. This graph shows trends at Toronto Pearson Airport from 1993 to 2012:

SENES 2012 Toronto's Future Weather & Climate Driver Study rainfall values and trends do not agree with Pearson Airport data values and trends provided by Environment Canada - Days with greater than 25 mm rainfall.

The data shows that the number of 25 mm days has increased a bit as shown by the dotted trend line- but the R-squared is only 0.016, so that is a very weak trend. What about absolute numbers? The average has been 4.1 days over this 20 year period, so the SENES current climate value of 16 days and the future value of 9 days is off the chart and going in the opposite direction.

What about other predicted daily rainfall trends? SENES predicted maximum daily rainfall would increase from 66 mm per day to 166 mm per day from 2000-2009 to 2040-2049. Here is the data just prior to and through the first period:

SENES 2012 Toronto's Future Weather & Climate Driver Study rainfall values and trends do not agree with Pearson Airport data values and trends provided by Environment Canada - Maximum Daily Rainfall

The daily maximum rainfall trend is flat and essentially random with r-squared of 0.00001. The average maximum daily value is 42.5 mm which is much less than the existing maximum SENES value, but the prior observed maxima in the mid 60's range do correspond to the SENES 2000-2009 value. Including the 2013 July 8, 2013 value would also support the upward direction of maximum daily values at Pearson (126 mm observed), but data at other Toronto gauges (only 51 mm was recorded in at the Toronto East York Dustan climate station (ID 6158751) for example).

The trend in daily maximum can also be assessed by the change in return period values representing common 2-year to rare 100-year return period intensities. The following table shows trends in 24-hour intensity values for 4 periods up to 1990, 2003, 2007 and 2013. The intensity trends are flat or decreasing as the last 23 years of record have been added, suggesting the maximum daily rainfall depth is not increasing as suggested by the SENES climate model.

When the basic values are so far off the existing data and initial trends predicted by climate change models, one has to seriously question the value of the weather prediction exercise. And given IPCC says 25 mm storms will increase, the SENES' Toronto study says they will go down, and real data shows no trend in these frequent events (i.e., the 2-year intensity is flat 1990 to 2013), you have to wonder that the value is for climate model predictions. Environment Canada provides a similar caution on Global Climate Models (GCMs) in the CO2 / Climate Report saying:

"GCMs are unable to resolve convective storms and hence provide little conclusive guidance on future response of such storms to warmer climates." Environment Canada.

Looking at average maximum daily values, the SENES data is more in line with Pearson Airport data for existing values as shown below. But the Pearson data shows no upward trend as would be expected if the average daily maximum is to increase from 48 mm per day now to 86 mm per day in the future period. The actual data trend is very flat and random:

It would seem that despite SENES' efforts in downscaling a Toronto climate model, there is still little conclusive guidance that can be seen and that can help inform drainage design standards and flood risk mitigation efforts. While it is understandable that predicting extremes is not possible for extreme weather events, the fact that the average rainfall trends are not moving as climate change models predict is a concern.  The premise of IPCC and others is that if the weather means change so will the weather extremes and the temperature changes will drive rainfall changes - so if data is actually showing the rainfall mean parameters are constant, the conclusion must be that i) temperature changes are not driving rainfall changes, and ii) rainfall extremes are not on the rise. This would be consistent with Environment Canada's earlier conclusions:

"Weather events beyond the expected range of weather behaviour to which local ecosystems and socio-economic infrastructure have adapted over time can have major ecological, social and economic impacts. Some of these impacts can be beneficial, but most are deleterious.Some of the recent climate trends and events, internationally and within Canada, cannot as yet be distinguished from those that could occur due to natural climate variability."

Separating the facts that there are indeed impacts from extreme weather that society has not adapted to (system capacities are too small for old weather and today's weather), from the premise of many that the weather has changed significantly due to climate change is an ongoing dilemma for those charged with advancing data-driven, evidence-based approaches to flood risk mitigation.

****

Those linking the 2016 Fort McMurray wildfire directly to climate change factors should strive to follow a rigorous review process as followed by Environment and Climate Change Canada in their climate report. ECCC offered the following:

"Average annual forest losses in Canada due to wildfire since 1980 is about 2.4 million ha. This
appears to be a significant increase from the average losses in the decades prior to 1980, at least partly due to a long term natural cycle involving an aging Canadian forest more prone to fire. However, there is also evidence that climate may be an important factor. Annual loss rates vary considerably from year to year, largely due to changes in fire weather conditions."

****

More?

SENES predicts changes in extreme rainfall too - check out link to this post for actual trends in extreme rainfall (IDF frequency analysis for Toronto City / Bloor Street and Pearson Airport climate stations). We show that even with the large July 8, 2013 event included, the daily trends are down or flat at Pearson and consistently down in central Toronto.

Given the facts on rainfall trends, we clearly need Design Standard Adaptation instead of Climate Change Adaptation to address the current extreme weather impacts.

Parliamentary Budget Office gets it wrong on Saskatchewan rainfall trends. Recent report contradicts Environment and Climate Change Canada's Engineering Climate Datasets.

Urban flood risk under climate change - Mississauga study ignores basics of hydrology and floodplain hydraulics to say a lot about nothing.

Design Standard Adaptation vs. Climate Change Adaptation for Urban Flood Risk Mitigation

New design standards are tigers.
Old ones are lambs.

New analysis on historical flooding during Toronto extreme weather, and observed wastewater flows in Ottawa prove it: Design Standard Adaptation is needed for urban flood risk management instead of Climate Change Adaptation - the same can be said for other southern Ontario municipalities.

That is, upgrading infrastructure capacity is required to account for significant increases in level of service, as opposed to upgrading for rainfall intensity trends which have been static. But rain causes flooding, right? Wrong. Let's look at the facts.

Rain doesn't directly cause flooding. Rain causes runoff, runoff accumulates as flow in drainage systems (or as extraneous flow in wastewater systems). It is ultimately infrastructure flow conveyance capacity, or lack thereof, that causes flooding. Both runoff conveyance capacity and extraneous flow stresses have changed significantly over the decades in Ontario and other jurisdictions, due to new design standards.

So why is there a fixation only on rain and climate when discussing adapting for flood risk? Clearly, other processes and factors related to urban hydrology (increased runoff) and infrastructure hydraulic capacity (constrained sewers and blocked overland flow paths) can better explain flooding instead of rain and climate. Yes those are quantifiable factors.

But let's break it down, showing only how design standards have addressed flow stresses and system capacities by considering:

1) Rain intensities ARE NOT increasing

2) Design standard capacity (level of service) HAS increased

3) Historical flooding is concentrated in areas with OLD STANDARDS and low levels of service

4) Pre-1980's areas need adaptation to today's more robust design standards

1) Rain intensities are not increasing

Has rainfall intensity increased in southern Ontario? Environment and Climate Change Canada's Engineering Climate Dataset version 2.3 say NO! There are more statistically significant decreases in intensity than increases, especially for the short duration intensities that drive urban flooding. Here is the data:

Short duration Southern Ontario rainfall intensities trends are mostly insignificant (randomly up and down) and are decreasing for short durations linked to urban flash flooding in overland drainage and sewer systems.

More statistically significant DECREASES in rainfall intensity are observed than increases.

Annual maximum rain intensities are DECREASING for all durations of 5 minutes to 24 hours at the long term Toronto climate station. Decreasing trends are statistically significant for the 6, 12 and 24 hour durations.

2) Design standard capacity (level of service) HAS increased

Storm Drainage / Runoff Flow Conveyance

Many municipalities had storm sewer capacities based on 2-year to 5-year return period rainfall intensities. This basic level of service for the 'minor' underground convenience system is characteristic of urban drainage system build before the 1980's, when dual drainage design emerged, adding 'major' overland flow capacity to the level of service to handle extreme rainfall. The earliest a Toronto-area municipality incorporated overland flow capacity into its design standards was 1978. Typically, a 100-year return period level of service is now provided for the major system. This represents about a 250% increase in system capacity as shown below.

Design standards increase level of service over time significantly - about 250% for old, pre-1980's 2-year minor-only systems to 1980's dual drainage 100-year systems, including overland flow component.

This is an excerpt from a late 1970's dual drainage standard in Ontario:

Dual drainage design standard incorporating minor sewer and major overland system capacity to avoid flooding into basements during 'heavy storms'.

Other cities have moved to the 100 year capacity standard through the 1980's. Calgary describes the chronology of drainage standard improvements, indicates improved drainage capacity standards in 1988: "The designed capacity for storm drainage systems in new communities is increased to handle one-in-one-hundred-year rainfalls (the former standard was one-in-five-year rainfalls - in some of the older communities, the standard was one-in-two-year rainfalls)."


Sanitary Drainage / Wet Weather Stress Reductions

Extraneous flows in wastewater systems (that stress infrastructure capacity, causing back-ups) have decreased dramatically as a result of updated design standards, resulting in a significant increases in level of service during extreme wet weather (i.e., lower flood risk in newer subdivisions). The transition to fully separated sewers from partially separated sewers, i.e., connecting foundation drains to the large storm sewer instead of the smaller wastewater sewer before the mid 1970's, decreases the 100 year extraneous flow in the wastewater system by 82% based on Ottawa's extensive monitoring and analysis. This is a significant reduction in flood stress in newer, post mid-1970's subdivisions.

Extraneous inflow and infiltration to wastewater system sanitary sewers decreased dramatically with complete sewer separation (foundation drains connected to large storm instead of smaller sanitary sewers).

Fully separated sanitary sewer systems have high level of service.

The lower extraneous wet weather flows, result in less sewer surcharge and basement back-up flood potential, as shown in the difference in return period level of service in systems with different design standards. Newer separated sewer systems have a 100 year level of service while older partially separated sewers (with 550% more wet weather flow) have a lower level of service - the capacity varies by system and by catchment size, showing in larger areas where extraneous flow are cumulative, the level of service is less than 50 year in example systems. Results are in the table at right. 

3) Historical flooding is concentrated in areas with OLD STANDARDS and low levels of service

Flood reports across the City of Toronto data for May 2000, August 2005 and July 2013 extreme storms were used to estimate the date of construction and the era of the drainage design practices. The age of watermain installation was used to estimate era, recognizing that in some instances of watermain replacement have occurred since the time of the original drainage design. The following map shows the era of watermain installation and flood sites.

Toronto Watermain Installation Dates (Estimate of  Drainage Design Standard Era) and Historical Flood Reports

This table shows the proportion of addresses reporting flooding in those three events, normalized by the total number of addresses in each era. Post-1980's construction show decreasing relative flood risk.

What does it show? Pre 1980 areas (1941 - 1980) have relatively higher flood risks and newer post-1980 areas have lower risks, reflecting better design standards. Why such low flooding in old combined sewer areas? Perhaps CSO relief in those systems, perhaps that August 2005 and July 2013 storms did not hit downtown as hard? Those are some possibilities.

4) Pre-1980's areas need adaptation to today's more robust design standards

Old urban areas built with only 2 year storm sewer capacity may have only 40% of the runoff conveyance capacity of newer, post 1980's areas that have 100-year dual drainage conveyance systems (100 year rain intensities and flow capacity can be 250% above 2 year capacity systems). And old areas built before the mid 1970's, with partially separated sanitary sewers, can have on average over 550% greater extraneous wet weather loads, stressing the wastewater system significantly during 100 year storms.

Since rainfall intensities have not increased, and design standards for storm and sanitary systems have changed dramatically since the 1970's and 1980's, Design Standard Adaptation is needed for urban flood risk management instead of Climate Change Adaptation. Here we summarize the whole post in a single cool bar chart:

Storm runoff conveyance capacity has increased with new standards, and sanitary extraneous wet weather flow stresses (inflow and infiltration) have decreased with new standards, while rainfall intensity conditions have remained static in Southern Ontario - obviously design standard adaptation is needed in older urban areas to mitigate urban flood risks including sewer back-up and overland flood perils. Runoff capacity has increased 250%, and 82% of sanitary flow stresses have been eliminated, due to current design standards.

***
More details: runoff increases with intensification, with the amount of impermeable, high runoff surfaces more than doubling over a 50 year period in some municipalities:


Rainfall intensity increases have been been reported by insurance media, confusing theoretical shifts with actual Environment Canada historical data:

Storm intensity not increasing - factual review of engineering data - Canada and Ontario from Robert Muir

Myth Busting on Climate Change and Flooding - aka Nutella is Really Sugar and Oil !

Healthy? or Bumgravy?

Media and advertising can convince you of anything. Like "Nutella is wholesome and good for you" - made with milk and nuts, when the first 2 ingredients are actually sugar and oil - its more like Bumgravy!

Here's our top list of myths (spread through the media like sweet, oily Nutella) about climate change and flooding that deserve some truth:

(1)

Myth: Rain intensity and frequency has increased due to climate change (MOECC, Environmental Commissioner of Ontario, Ontario Government, IBC, ICLR, etc.).

Infographic Bumgravy.
100% data-free !!!!

Truth, rain intensities are not increasing according to Environment and Climate Change Canada's published research based on the Engineering Climate Datasets (version 2.3).

(2)

Myth: Extreme weather events that occurred every 40 years are now occurring every 6 years due to climate change (IBC, ICLR in Telling the Weather Story).


Truth: Maybe worst blunder ever published! IBC / ICLR mixed up a theoretical bell curve shift with actual data - the worst part is they won't admit it and a chief economist at major Canadian bank has repeated the false data claim on historical trends.

(3)

Myth: We are having 20 times more storms now than we used to and that is causing insurance rates to go up.

Truth: The balance sheets of P&C companies is more complicated that this, especially plummeting fixed income earnings in a low interest rate environment that cannot offset underwriting losses anymore .. but that is off track. Environment and Climate Change Canada, through a complaint to the CBC Ombudsman, has corrected this bogus statement as we are not getting more storms. Period.

(4)

Known flood zone. Deeper flood weeks before on May 28-89.
Help stop the Bumgravy Train and tell the truth about flood
causes in Canada ! This was only between a 2 year and a 5 year
design flow rate for the Don River at the Todmorden gauge.

Myth: The GO Train Flood on July 8, 2013 was due to unprecedented conditions is evidence of climate change impacts to weather (Metrolinx, Environmental Commissioner of Ontario).

Truth: A higher flood occurred on May 28-29 just weeks before - so not unprecedented. It was less than a 5 year flood flow rate in the Don River per the Todmorden gauge records - so not a climate extreme. Rail flooding has been documented since the early 1980's flood inquiry to Premier Davis. This was an operational mistake, sending a train into a documented high risk zone at the wrong time during a moderate flow event.

(5)

Myth: Aging infrastructure is reducing capacity causes flooding (most media).

Truth: This has never been cited as a cause of flooding in any of the Municipal Class EA's .. is it possible an advanced City that spends a million dollars per study missed this cause of 'aging'? Check out the Toronto program or Council reports and see if there is any example of 'aging' and share it with us.


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More: Chestnut cracking on sewer infrastructure capacity.