Toronto Stormwater Tax - Underhanded Double-dipping or Transparent Equitable Service-Based Fee?

While a Toronto Councillor has lifted his middle fingers to a stormwater 'tax' in the City of Toronto, suggesting such as charge is underhanded and a way of charging for a service residents already have, he's wrong.

A proposed stormwater utility fee based on hard surfaces is a more equitable way of allocating costs for drainage services in Toronto - currently residents and businesses pay for stormwater management capital works through their water bill - yes, depending on how much water you use. Water consumption has nothing to do with runoff, whereas hard surfaces do.

That is why many Canadian municipalities have implemented stormwater rates to fund operating programs and capital works related to stormwater. Local municipalities near Toronto with stormwater rates in place include Richmond Hill (flat rates), Markham (flat fees for residential and variable fees for businesses of various sizes), Mississauga (based on flat fee tiers for residential and variable based on hard surfaces for other properties), Kitchener and Waterloo (similar approach as Mississauga), Aurora (flat rates), St. Thomas, and London. And stormwater fees are in the works for Guelph and Vaughan.

Do these fees fund existing services? Sometimes they do and municipalities transfer program funding from existing funding sources (water bill or tax bill) to the new dedicated stormwater fee. In that way it is hardly underhanded, but rather transparent and equitable, where the fee is in proportion to the service being provided.

Toronto's project backlog for basement flood protection has grown considerably as Municipal Class Environment Assessment studies are completed across the city, identifying infrastructure upgrades that come at a considerable cost. As examined in other posts, design standard upgrades are required to address level of service limitations in many areas across the City of Toronto. This is especially needed in areas with partially separated sanitary sewer systems with high extraneous wet weather flow rates that overwhelm drainage systems during extreme weather events.

Extreme rainfall is not more severe in Toronto, so there are not new rainfall stresses on infrastructure - there are stresses due to intensification and urban growth over decades as noted in previous posts. Nonetheless, there is a considerable legacy of designs with limited levels of service that should be addressed with sustainable, equitable service-based funding. A Toronto stormwater charge based on hard surfaces, sometimes called impervious surfaces, will be an improvement over current funding through the water bill.

Sydney, Nova Scotia Record Rainfall Not Record for the Region - Trends Decreasing - No Climate Change Impact

Expanded post with regional trend data.

CBC News published a story describing record rainfall due to the remnants of Hurricane Matthew. While the 225 mm of rainfall recorded over the short Sydney rain gauge  monitoring period is a record, the record in the region in Halifax, Nova Scotia was 239.5 mm back in September 1942. Environment Canada's Engineering Climate Datasets provide historical records - an excerpt of Halifax data is shown below.

The full data is available at the following site and can be downloaded by region:

Trends in annual maximum extreme data in Halifax are up and down according to data included in the Environment Canada datasets - trends are up for short durations of less than 1 hour and down for longer durations as shown below:
It is likely that if the 1942 event was not recorded then longer duration events would have increasing trends too in Halifax. This helps illustrate the random nature of recording records. Records should be reviewed with caution unless the observation period is very, very long.

Sydney records only began in 1961 missing the 1942 event, suggesting the 2016 event is a record for that area ... well it is, but only because the observation period is relatively short to assess extreme events ..... if a tree falls in the forest and noone is there to hear it we think it really didn't occur.


In a recent report by CTV News Atlantic about flood damages in Sydney, Nova Scotia, an incorrect statement on extreme rainfall trends is made.

"(Mayor of the Cape Breton Regional Municipality Cecil) Clarke said the weather is a reminder that climate change is contributing to more intense storms on the East Coast."

This contradicts Environment Canada scientists' analysis of extreme rainfall trends in the region, as published in Atmosphere-Ocean in 2014. In that review of the Engineering Climate Datasets scientists say for short duration rainfall intensities that govern urban flash flooding, trends are decreasing:

"The decreasing regional trends for the 5- to 15-minute duration amounts tend to be located in the St. Lawrence region of southern Quebec and in the Atlantic provinces." and then

"The decreasing regional trends for the 5- to 15-minute durations are mainly located in southern Quebec, most of the Atlantic provinces, and in southern Manitoba and Alberta."

Environment Canada reports the "maximum non-significant decreasing trend value in the AMS (Annual Maximum Series) amounts of −4.4% per decade (-0.44% per year) for the 5-minute duration."

Drilling down into the local area, Sydney has no statistically significant trends in annual maximum rainfall intensity, based on Sydney CS Station Number 8205702 data trends.
(see file idf_v2-3_2014_12_21_820_NS_8205702_SYDNEY_CS_t.pdf in the dataset)

It is important to note that increasing observations of more extreme rainfall events over time does not necessarily indicate a change in the underlying rainfall behaviour, e.g., due to climate change or even other factors, but rather 'regression to the mean'. Short rainfall records of several decades fail to capture extreme events as a simple matter of statistical probability - longer records, and more observations capture more extreme events. For natural phemonema that have skewed probability density functions describing the rare nature of extreme events, it can takes many decades to accurately characterize the behaviour. Generally, short records with high coefficients of variation in the random variable (rainfall intensity) will underestimate the true extreme values the most. In the field of catastrophic loss estimation, and as published by Fleming in the journal Variance, a peer-reviewed journal published by the Casualty Actuarial Society:

"Also,the most likely sample average value for any small sample from a skewed population will be below the mean of the skewed population being sampled. Experienced actuaries are aware of these issues. However, we have to be on guard and not fall back on easy assumptions that are appropriate for results from symmetrical distributions."

Environment Canada Engineering Climate Datasets show that it took twenty years for a 100 year statistic to be exceeded in Sydney - observations started in 1961, and 100 year 30-minute to 24-hour intensities were observed in 1981. That raised the bar on the baseline conditions, making it harder to exceed the 100 year statistic. Then in 2012 the 100 year statistics were exceeded for only 1 and 2 hour durations, meaning it is becomes harder to exceed over time as a longer record better reflects the underlying characteristics and extreme value probabilities. The 2016 Hurricane Matthew statistics should exceed the 100 year statistics again - raising the statistics to better reflect the underlying distribution of extremes. But with only 53 years of record since 1961 (1992 and 2010 are incomplete), the chances that a 200 year or 500 year extreme storm has been observed are rare. This is a reminder that regional storms can be considered in floodplain management and urban drainage design. If Sydney drainage systems (floodplains, infrastructure) were designed considering the 1942 Halifax storm as extreme regional conditions, perhaps flood damages would not be so severe.

Windsor and Tecumseh Flood Reporting Exposes Gaps in Media Meteorology Math and Memory

Reporting on the Windsor and Tecumseh flooding in September 2016 highlights the gaps in extreme weather reporting in Canada .. and amnesia regarding past events... and the unwillingness to explore other factors affecting flooding, like hydrologic changes.

The Facts: CBCNews reports 190 mm fell in Tecumseh 80.8 mm in Windsor

The Fishy: CBCNews reports "I've never seen anything that intense in the 35 years I've been in this region," (Tecumseh Mayor Gary ) McNamara said. "This is unprecedented."

But the event was not unprecedented in the region. Water resource management and civil engineering professionals know that the region has recently experienced a much greater storm. Even CBCNews reported on the anniversary of the Harrow Storm 27 years ago : they reported in July 2014 on the Harrow Storm of July19-20, 1989:

"A massive, stationary storm dumped 450 mm (17 inches) of rain on Harrow and Colchester South in the matter of hours in southwestern Ontario.|

The Facts: CBCNews reports 63.4 mm of rainfall fell at Windsor Airport

The Fishy: "That beat the record for that date in history, which was formerly 36.8 mm set back in 1973." ... this is a fishy statement because drainage systems are not designed to specific calendar day rainfall characteristics. In fact annual series of maximum daily, hourly, and 5 minute intensities are used to characterize weather. This is a typical headline-grabbing technique such as when the July 8, 2013 storm in Mississauga was reported to be triple the maximum record ... ummm... for a calendar day that usually does not receive hardly any rain. This inaccurate reporting sets up the 'anchoring bias' in the readers' perception of the rarity of the event.

The Weather Network's Chris St. Clair says on the October 1, 2016 morning broadcast that the Windsor storm was "unprecedented" ... its not clear if he meant unprecedented for September 29th's, which is irrelevant, or unprecedented for the region on any calendar day which is plain wrong. In a later report he calls the rain event 'unbelievable'. The Weather Network started broadcasting in September 1988, so perhaps it should be aware of the Harrow Storm in 1989.

The Weather Network's Kim MacDonald reports that Tecumseh received twice its average monthy rainfall in 15 hours on the October 1, 2016 broadcast - this reporting is another example of an 'anchoring bias' - comparing a rainfall statistic to another statistic that is irrelevant to drainage design - no drainage systems are designed for monthly totals, instead they are designed based on annual extreme time series and derived extreme value statistics to project rare conditions that may have not even occurred yet. See our post on heuristic biases in rainfall reporting.

Kim MacDonald notes that 1700 flooded homes were reported in this 2016 storm. In the 1989 Harrow Storm CBCNews reported 2000 flooded homes. Unprecedented?

Big picture questions for Essex Region could include whether the 100 year regional storm design standard is big enough for the region. Other conservation authorities regulate to larger storms - Upper Thames uses the 250 year storm - most others use Hurricane Hazel, which is perhaps a 500 year storm. Other regions use large historical storms like the Timmins Storm. Perhaps it is time for the "Windsor Storm" based on the September 2016 storm.

Another question - are local flood hazard limits keeping up with hydrologic changes to the region over decades? We explore this for many Ontario cities here - but here is a map of the growth from the 1960's to late 1990's. Pink areas are expanded urban area.

Consider this: when your design standard is so low (Essex Region has the minimum 100-year flood standard in Ontario according to the Provincial Policy Statement on natural hazards), the importance of expanded development and intensification in existing development areas is an even more important factor when considering increased runoff and flood risk. Why? Because pervious land uses can absorb some fraction of 'small' 100 year storm but not much of the large storms used in other regions. Those using Hurricane Hazel design storms which saturate the ground with anecedent moisture conditions (US Soil Conservation Service AMC III conditions to be exact) do not have as significant an increase in runoff following development. Those using 100 year storm, like Essex Region, use the drier AMC II conditions in hydrologic models, meaning that the soil-vegetation surface can absorb relatively more ... until it is paved over.


Check out previous posts on Windsor extreme rainfall:

Environment Canada corrects CBC story that storms are getting worse in the Windsor Region over decades.

Up until now Windsor Airport had decreasing extreme rainfall trends like most of southern Ontario, according to Engineering Climate Datasets. As summary is below. Here are more details.

climate change Ontario

Below are the underlying Windsor Airport trend graphs up to 2007 from Environment Canada (the highlighted durations of 10 minutes, 2 hours, 6 hours and 12 hours are the statistically significant decreasing trends ins annual observed maximum values - these correspond to the dark green cells in the table above):climate change Windsor
It will be interesting to see if companies offering sewer back-up insurance or overland flood insurance will pay for all claims related to this storm. Runoff rates obviously exceeded the drainage system capacity in many areas, meaning flood damages were due to surface water entering properties, which is excluded from most homeowner policies. Surface water flood damage endorsements are available from Aviva, Intact and RSA. Following recent extreme events, these companies have tried to clarify coverage exclusions to homeowners, encouraging them to sign up for overland, surface water flood coverage. It is unclear how state of emergency / disaster relief funding would offset insured and uninsured damage claims.

Does Climate Change Cause More Severe Storms? NOAA Says Yes In Louisiana But Not in Colorado. Canada Mixed?

The 2016 extreme rainfall in Louisiana has been deemed by NOAA to be more likely and severe due to change climate, while the 2013 extreme rainfall in Colorado has been deemed less likely. Why the different behaviour? Like in real estate, its all about location, location, location. Trends are not uniform across the entire continent - Louisiana is influenced by the Gulf of Mexico, and Colorado isn't.

The 2016 Louisiana rainfall event dropped more than six inches of rain in some regions August 11, 2016 and Baton Rouge received over 11 inches of rain August 12. Such an event has been analyzed to be more likely, with a shorter 'return period', meaning a higher probability of occuring. Specifically the 2016 Louisiana storm was assessed to have a 30 year return period today (i.e., 1/30 = 3.3% chance of occurring), while only a 50 year return period in the past (i.e., a lower 1/50 = 2% chance of occurring). Details are here.

Louisiana rain frequency shift - 3 day rainfall.
Details are on the NOAA website, including the graphic above.

But a NOAA-led study published in the Bulletin of the American Meteorological Society indicated that "The probability for an extreme five-day September rainfall event over northeast Colorado, as was observed in early September 2013, has likely decreased due to climate change." That storm dropped 17 inches of rain.

Details of the Colorado rainfall analysis are here, indicating a 12% decrease over the last century:

"Despite a warmer and moister climate, the frequency of September heavy five-day rain events does
not increase in the simulations but substantially declines in northeast Colorado (Fig. 5.2c). Using the model’s 95th percentile of five-day rainfall totals, we find a 12% decline in occurrence during recent decades compared to the late 19th century."

And the following:

"... a slight decline in intensity of the maximum five-day precipitation over the central Great Plains
during summer is also projected (Sillman et al. 2013), emphasizing that global and annual perspectives of climate change may not always pertain to events at a specific place and time."

Research by Peterson shows regional trends in flood magnitude over decades that support the decreasing Colorado rainfall trends:

How to Interpret: "Trend magnitude (triangle size) and direction (green = increasing trend, brown = decreasing trend) of annual flood magnitude from the 1920s through 2008. Flooding in local areas can be affected by multiple factors, including land-use change, dams, and diversions of water for use. Most significant are increasing trends for floods in Midwest and Northeast, and a decreasing trend in the Southwest."

These USA extreme events and trends highlight the difference in regional impacts of a changing climate. In Canada, precipitation analysis by Vincent and Mekis showed less extreme daily rain, although more days with rain:

"The analysis of the precipitation indices for 1950–2003 reveals more days with precipitation, a decrease in daily intensity and a decrease in the maximum number of consecutive dry days."

Research has shown regional trends in annual maximum observed rainfall amounts as well. Environment Canada scientists indicate the following in Atmosphere-Ocean indicating increases and decreases:

"Both the southwest and the east (Newfoundland) coastal regions generally show significant increasing regional trends for 1- and 2-hour extreme rainfall durations. For the shortest durations of 5–15 minutes, the general overall regional trends in the extreme amounts are more variable, with increasing and decreasing trends occurring with similar frequency; however, there is no evidence of statistically significant decreasing regional trends in extreme rainfall amounts. The decreasing regional trends for the 5- to 15-minute duration amounts tend to be located in the St. Lawrence region of southern Quebec and in the Atlantic provinces."

It is important to distinguish between 5-day rainfall trends, noted in the Louisiana and Colorado analyses, 5 minute to 24 hour rainfall trends in the Environment Canada analysis. In the Canadian data the trends can be mixed across a single weather station depending on the duration. This table shows that variability in long term Canadian climate stations:

The data shows, for example, decreasing very short duration and longer duration trends at Toronto Pearson Airport (5 minute, 6, 12, 24 hour), but increasing mid duration trends (10 minute to 2 hour). Ottawa has decreasing short duration trends - suggesting less severe urban flooding potential - and increasing longest duration trends.

Overall, Environment Canada indicates "a general lack of a detectable trend signal" in short duration rainfall (meaning 5 minute to 24 hour) that is important for engineering infrastructure design. In Southern Ontario, there are more statistically significant decreases in annual maximum rainfall than increases:

In Southern Ontario, the increases in extreme rainfall are generally over longest durations (6, 12, and 24 hours) that is not critical for urban flash flooding - in contrast, the shortest duration trends show decreasing extreme rainfall.

Previous posts suggest that the increase in flood damages in Ontario cities can be related to multiple factors such as land use change (also noted by Peterson regarding USA Floods). For example:

Urbanization and runoff explain Ontario flooding

Ontario, Canada city land use change and flood risk

Urbanization, Runoff, Overland Flow and Flooding - How Sprawl of Ontario Cities Drives Flood Risk and Insurance Losses in Urban Areas

Readers of this blog have seen these basic process described several times: (1) rain transforms into runoff when it hits the ground, (2) runoff accumulates and flows in rivers or municipal drainage infrastructure, (3) the capacity of the flow systems determines whether flow "backs up", "surcharges", "spills", or generally flows uncontrollably to where we don't want it to go, causing flooding.

Using Environment Canada's data and research, we have shown that rainfall intensities have not increased in southern Ontario here. In fact there are more statistically significant rain intensity decreases than increased south of 44 degrees. So the rainfall influence on runoff is not increasing. But runoff has been increasing after decades of urbanization under the today's stable or decreasing rainfall intensities.

The following maps show urban expansion in Mississauga, Oakville and Burlington Ontario from 1966 to about 2000 (data varies from 1999 to 2002). The overland flow system path based on Ontario conditioned digital elevation model is superimposed on the land use map so that the impact of urbanization and runoff into the drainage system can be considered.

 The effect of urbanization in Mississauga on runoff would be most acute in the smaller watersheds (e.g., not the Credit), where the upstream urban area has increased significantly since 1966.

Likewise in Oakville - Bronte Creek, a large watershed more slightly influenced by the city's sprawl, has not been affected to the same degree as the smaller Fourteen Mile Creek to the west, where a high relative change in land use over that smaller watershed has occurred throughout the city.

Same in Burlington - many small creek watersheds originating off the escarpment have dramatically increased urbanization over three decades. Burlington is characterized by creeks that have been realigned, straightened and encroached upon. These can be expected to be more sensitive to increased runoff rates due to expanded urbanization.


Parts of Hamilton have been urbanized up to the watershed divide (black line) by the late 1990's / early 2000's. How does this affect runoff into the old 'core' built to pre-1960's standards?

Hamilton, wider perspective. Some wetlands remaining upstream of Dundas? :

Richmond Hill (Lake Wilcox near upper middle of map). Some urbanization around the lake flows to the Humber where flow impacts would be muted, while other areas to the south flow flow to headwater tributaries of the Don and Rouge: