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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:

ftp://ftp.tor.ec.gc.ca/Pub/Engineering_Climate_Dataset/IDF/IDF_v2.30_2014-12-21/IDF_Files__Fichiers/

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.

***

Over time there is a regression to the mean. The incidence of hurricanes has been in a lull as pointed out by Pielke Jr. in the graph below:

is hurricane frequency increasing in US - no

Hurricane Harvey a category 4 storm is expected every 9 years or so. So it is due given the gap in days since a hurricane.

Secret is Out ! Urbanization and Runoff Explain Increased Urban Flood Risk in Southern Ontario

Mapping urbanization changes
over time can explain flood risk
trends, so we can see things "the
way they are" and gain insight into key
management needs for flood mitigation.

"Only the small secrets need to be protected. The big ones are kept secret by public incredulity."(attributed to Marshall McLuhan)

Could it be that we have ignored the obvious "secret"? That is, the effect of increased urbanization on urban flood risk in Ontario. It seems so.

Mapping of urbanization patterns in that Greater Toronto, Golden Horseshoe, and the Big K-W areas shows obvious, dramatic increases in watershed urbanization over a thirty year period from 1966 to the late 1990's. In some Toronto watersheds, urbanization increased by 986%, and that does not even consider intensification within previously developed areas. This analysis begs the question: "Why is there such a disproportionate focus on global climate change impacts to local extreme weather (now disproved) to explain flooding, compared to a focus on the obvious land use changes on hydrology, and increased runoff under historical climate conditions?"

The following map shows the increase in urbanization from 1966 according GIS mapping converted and shared by Ducks Unlimited (source is the Canada Land Inventory Land Use 1:50,000 scale mapping for Southern Ontario), and to 1999-2002 per the SOLRIS Version 1.2 land cover GIS mapping, as compiled in the Ontario Land Cover Compilation Version 2.0 and available through Land Information Ontario.

Greater Toronto Area Urban Area Growth in TRCA watersheds and Flood Risk Influence on Urban Flooding

Greater Toronto Area Urbanization and Flood Risk

Urban Growth in TRCA watersheds and Flood Risk Influence on Urban Flooding

Clearly, the amount of urbanization has increased dramatically in southern Ontario watersheds, including many that have experienced flooding in the past decades. In about 30 years, urbanization has increased by 986% over and above the 1966 amounts in the Rouge River Watershed, and by 696% in the Duffins Creek Watershed. In Toronto area watersheds, unlike Rouge and Duffins, the increase is also dramatic - not as much for the percentage increase, but for the relative coverage. The Highland Creek Watershed increased by an added 124% over the 1966 coverage, resulting in over 88% urbanization coverage. Similarly, Mimico Creek Watershed urban areas expanded by 135% more, also resulting in over 88% urbanization by 1999-2002. The following table shows the TRCA watershed breakdown.

How about Mississauga where there was flooding in 2013? Well, Etobicoke Creek Watershed added 341% urban coverage resulting in 64% coverage by 1999-2002. Yes it should seem greater, but we have not counted the valley areas or other large open or vegetated areas within the urban areas (e.g., hydro corridors, etc.). We have also subtracted these 'greenspaces' from the 1966 data to avoid over-reporting the 1966 coverage, as the 1:50,000 source data was not as detailed as the the SOLRIS data that classified land used down to a 15 m cell resolution. And the Cooksville Creek area in Mississauga? In 1966 urban development extended generally up to Dundas Street, while 30 years later it extended to Highway 407 as shown in the image below.

Mississauga Urbanization 1966 to 1999-2002.

Do the math. Nearly an order of magnitude increase in urban coverage in one large watershed. Doubling of urban coverage in all but one other TRCA jurisdiction watershed. And even more intensification within the old urban areas. Runoff potential has increased dramatically as a result. This explains increased flood risk in urban areas.

While stormwater management controls have been put into place for some later developments to mitigate hydrologic impacts, these are finite, perhaps up to 100 year storm standards - extreme weather events can be above or below that threshold, meaning flood damages can occur for the large events. Furthermore, many infrastructure components put in place decades ago are not sized to handle 100 year storms, and have been designed to overtop for high frequency, lower return period events (e.g., underpasses, local roadway crossings).

So why have folks jumped on the now-discredited conclusion that climate change has been driving local flood damages and losses, but ignored basic hydrology and effects of urbanization? Perhaps we can learn from Vit Klemes, perhaps our greatest hydrologist. He had reiterated his piece to the Canadian Water Resources Association (Implications of possible climate change for water management and development. Water News (CWRA), 11, 1, S2-S3) in his address to the International Interdisciplinary Conference on Predictions for Hydrology, Ecology, and Water Resources Management: Using Data and Models to Benefit Society,15–18 September 2008, Prague, Czech Republic. In this address, entitled "Political Pressures in Water Resources Management. Do They Influence Predictions?", he states:

"[the theorists] find it easier to play trivial scenario-generating computer games while the [managers] find these games much easier to finance... And so by happy collusion of interests, an impression is created that 'something is being done for the future' while the real problems are quietly allowed to grow through neglect of the present"

Neglect obvious present hydrology. Instead, generate theoretical climate change storm impacts .. with computer "games", i.e., models, or even basic high school math probability density function manipulation. And happily fund every climate change prediction or adaptation study.

***
NB - the newer urban areas have higher densities and greater runoff potential than the older ones:

York Region Urban Development Intensification 1952-2002 - Impervious Surface Area Coverage Doubles Over 50 Years

And intensification within established urban areas can increase runoff potential as well. This shows changes since the early 1970's across the 7 lots beside my house in east Toronto:

Redevelopment and increased urbanization in east Toronto - no residential, single lot stormwater management controls to mitigate runoff impacts to existing drainage system.

And this shows intensification in the GTA in an area developed in the early 1950's but undergoing redevelopment / intensification, expanding impervious area coverage, to this day:

Canadian Flood Underwriter - Can Fire Underwriters Survey History Guide Urban Flood Risk Management Model?

Can the history of the Fire Underwriter Survey provide a roadmap to a future Canadian flood underwriting model?

Fire Underwriters Survey (FUS) is a national organization and was formerly the Insurers’ Advisory Organization (IAO) and Canadian Underwriters Association. As noted on their site, "FUS provides data on public fire protection for fire insurance statistical work and underwriting purposes of subscribing insurance companies. Subscribers of Fire Underwriters Survey represent approximately 85 percent of the private sector property and casualty insurers in Canada."

The history of the FUA and the organizational and technical benefits offered to its members is described in this book:

http://www.fireunderwriters.ca/theunderwriters_e.asp

"The Underwriters, the history of the Insurers' Advisory Organization and its predecessors, the Canadian Fire Underwriters' Association and the Canadian Underwriters' Association," by Christopher L. Hives, 1985.

If "flood is the new fire" as far as Canadian insurance losses go (Fort McMurray 2016 notwithstanding), much can be learned in how the insurance industry developed the Fire Underwriters organization to organize, guide, educate, and support member insurance companies.

How did fire insurance evolve?

The first fire policy was written by the Phoenix Company in 1782 policy in Sr. John's, Newfoundland and the first Canadian company to offer fire insurance was the Nova Scotia Fire Insurance Association, founded in 1809 in Halifax. More players joined and by the mid 1800's it was apparent there was a need for standardization and organization - so in 1857 "in order to better serve the interests of the community and the participating companies, a joint body or association called the Halifax Insurance Board (was) formed".

Following a 1859 severe fire in downtown Halifax with payouts of £128,075 the board commented on causes and identified "the want of sufficient supply of water at the commencement and to a general want of management". It made recommendations for an improved city water supply for the city, more firemen, and water supply infrastructure along Barrack Street with branch lines exclusively for fires. Without these risk reduction measures, the board would increase tariffs (i.e., premiums).

The early Halifax example illustrates the partnership between government and insurance industry whereby standards for municipal services consider insurance industry needs, which it could be argued, mirror the financial needs of the economy, and the government's need to promote safety and security in the community as a whole.

Over the next century or so, a national organization was formed, evolved and grew (Canadian Underwriter's Association (CUA) founded in the late 1880's, and Insurer's Advisory Organization (IAO) in the 1970's incorporating CUA and independent members). In the late 1970s, lAO developed one of its first computer applications to determine whether a sprinkler system would function properly and if the water supply was sufficient. This replaced inefficient manual calculations.

One could draw parallels between the IAO's analysis of sprinkler fire suppression systems and the assessed benefits of flood prevention systems. In the case of large watersheds in the Toronto area, prevention features would include infrastructure such as the Lower Donlands Landform Berm, Black Creek Channel, and TRCA dams - all incorporated in JBA's flood defense layers. At the local municipal level, flood prevention features would include drainage and municipal infrastructure standards incorporated in new resilient communities, or upgrades for flood risk mitigation in communities build with lower standards (e.g., pre-1980's subdivisions with limited overland drainage design, and partially-separated wastewater systems).

Currently CGI Risk Management Services conducts Fire Underwriters Survey (FUS) services for the Canadian insurance industry, including assessment of municipal water supply systems including adequacy of available flow rates for structures in the community, and distribution system adequacy and reliability. This information helps guide community improvements and to establish "municipal gradings for insurance purposes", according to CGI.

The parallel in the context of urban flood risk assessment would be i) assessment of wastewater systems to safety convey extraneous flows during extreme wet weather events, without surcharging and causing floor drain sewer back-up, and ii) assessment of overland drainage systems to safely convey overland runoff ('major drainage system flows) to an adequate outlet like a channel or valley, without surrounding and entering buildings. Since the 1970's, computer assessments of wastewater system capacity has been pursued using the SWMM model, typically in the context of flood remediation or CSO reduction studies. Today, such models are more widely available, but even in jurisdictions like Toronto, they are only now being developed to cover the entire municipality and to be developed with robust standards. Over time, the risk characterization from such models could be used to establish a municipal grading for insurance purposes, likely at a block face level of detail. Overland flood risk models are only now becoming commonplace, including JBA's riverine and surface (pluvial) flood risk models based on 2D overland flow modelling.

The difference between CGI's fire risk assessments and flood risk assessments is that no flood risk assessments are tied to 'municipal gradings'. Municipal wastewater system assessments can result in infrastructure improvements, or when not cost effective, deferred projects. But neither condition is communicated to an insurance risk body, and the insurance industry is not known to participate as a stakeholder in the municipal environmental assessment studies that guide the improvement strategies. Similarly, the overland risk assessment available to those writing individual policies are not shared with municipalities to guide macro-scale, neighbourhood-level improvements to infrastructure that could mitigate risks and premiums. IBC's Municipal Risk Assessment Tool (MRAT) estimates municipal wastewater back-up risks but these are not used to set premium rates or identify specific municipal infrastructure improvements (i.e., MRAT provides generalized, regression-based "high-low" risk mapping for one type of flood risk but does not incorporate system hydraulics to assess upgrades, nor does it assess neighbourhood overland flood risks or remediations).

Given that fire insurance and underwriting support evolved over more than 200 years, and that technical assessments of some risk factors like fire suppression sprinklers emerged only 40 years ago, flood risk underwriting likely has decades to go before an effective partnership can develop between the insurance industry and municipalities and other levels of government.

"...our industry will undergo fundamental and radical changes which will severely test the mettle of all the players in the league. 'To be sure, the 'good old days' are gone forever. Today's conditions, regarded by many as 'abnormal' are, in reality, 'but a mild rain shower compared to the storms of the future ...obviously, the future is no place for the faintheaded, the rigid traditionalists and the seekers of the status quo. The survivors will be the courageous, the alert, the flexible, the imaginative,

the planners and the managers of change. With the continued support of its Members, lAO would like to be counted among the latter."

Ted Belton's comments on the status ofthe industry at the end of 1980, following all time high 1980/1981 loss ratios.

Given current flood loss trends, Mr. Belton could have been looking out 35 years to today when investment earnings are low (again) in this low interest environment, and when extreme rainfall losses are on the rise. Imaginative change is again needed to develop a flood underwriting strategy.

Low Insurance Industry Investment Returns Push Premiums Higher

It is common (convenient?) for the insurance industry to explain increased premiums due to storm frequency. In response to our complaint on inaccurate reporting from an insurance broker's newsletter, the CBC has acknowledged "Environment Canada verified that there has been no significant change in rainfall events over several decades" in a letter to us. People are catching on that we cannot just Blame it on the Rain.

So what are the real factors pushing damages and premiums higher? CityFloodMap.Com explores many factors that increase damages and add cost pressures in our letter the the Minister of the Environment and Climate Change. But there are factors beyond the physically obvious watershed hydrology and infrastructure hydraulics.

Macro economic factors affecting insurance industry investments are the unspoken factor that puts upward pressure on premiums for property and casualty insurers in Canada. Details are in Facts of the Property and Casualty Insurance Industry in Canada 2015 is published by Insurance Bureau of Canada (IBC).

Previously, insurance company investments earned double digit returns that subsidized underwriting losses. Today, those same investments earn low single digit returns and so now underwriting has to carry its own weight - this means that premiums from underwriting have to increase to compensate for lagging investment returns. This is an excerpt from the report (page 13) to explain the impact of low interest rates on return on investment:

"Return on equity comes from two revenue streams –
underwriting and investment earnings.

In 2013, underwriting posted gains for the 11th consecutive
year. The 2013 net underwriting revenue was $648 million.
Before 2003, underwriting posted losses for 24 years in a row.

On investment, 2013 was a year of relatively low returns of 3.1%.
Return on investment moves in lockstep with the yields for
3- and 5-year Government of Canada bonds, which have fallen
for the last two decades."

Sliding investment returns means underwriting has to carry its own weight on insurance company balance sheets.

RSA Fresh Water Flood Coverage Acknowledges "Concurrent Causation" in Flood Damage Claims

An article in candianunderwriters.ca describes the new RSA fresh water endorsement expected to be available to the large majority of RSA customers. It is encouraging to see the recognition that there has been 'concurrent causation' for flood damages:

"Some of the challenge we had with the floods in Alberta and in Toronto was this concurrent causation issue, where you had sewer backup happening at the same time as you had clean water flood coming in and you can't really say 'Part of it is brown water, part of it is clear water,'" the RSA representative said.

This represents progress in terms of characterizing the complexity of flood risks, but what is missing from the discussion (for Toronto table land type flooding as opposed to Alberta riverine flooding) is that:

Extraneous clear flow from groundwater infiltration
and inflow points enters the 'brown' sanitary sewer.

Comment 1) Sewer backup water during severe storms is often brown and clear together, because during extreme storms, the extraneous inflows to the sanitary sewer system dilute the typical brown water, typically by a factor of 10 to 1. For infrastructure managers, the clear water components is often called RDII, or rainfall dependent inflow and infiltration - this clean water component can peak at up to 5 L/s/ha in a partially separated sewer system during an extreme event. Because of this, separating clear water and brown water risks is always difficult to do in practice.

Clear water surface flooding enters doors and windows and
exits low lying upstream properties via floor drain.

Comment 2) The clear and brown water coming in typically occurs at different locations in the neighbourhood's drainage system. Low-lying areas with low exposed openings can allow clear water to enter buildings and then exits via floor drains. Those extraneous flows enter the sanitary sewer system and cause brown+clear water to enter downstream properties via floor drains. Because of this, a downstream property may be vulnerable to brown water backup, because of an upstream property's clear water risk.

RSA indicated that regarding the old sewer backup coverage:

Downstream sanitary sewer overwhelmed with brown and
clear water creates backup, entering property via floor drain.

"In the past, that endorsement was much broader and in some respects would cover flood not intentionally but did cover flood."

Comment 3) What this means is that for some insurers, the backup premiums may have been increasing to pay for clear water, overland flood damages. In my case, for example with a different insurer, the premium has increased 800% and the coverage limit has decreased for backup insurance - this could be explained by unintentional coverage of clear water, overland flooding in my city / neighbourhood. In an ideal world, RSA could decrease backup premiums by limiting coverage of uninsured perils like clear water, overland flooding, while pricing clear water flooding separately. .
Because of Comment 1 and 2, it will difficult to separate the different risk coverage

Just like cable TV, you can now pick and pay for your flood peril coverage:

"If you get Waterproof you get sewer backup and the flood, but if you don't want the Waterproof endorsement, if you don't want the flood, you can just buy limited sewer backup," RSA adds, saying that they are "putting a lot of emphasis" on training brokers.

Comment 4) This approach may meet RSA goals of limiting coverage for uninsured perils and increasing premiums for flood to help cover increasing costs during extreme events. In the end, the bottom line for the business is not dependent on having an optimal, precise vulnerability assessment for individual properties - all it needs is a sub-optimal net positive outcome on the portfolio. RSA is making an incremental adjustment toward a more sustainable, better priced risk model with the changes.

Not all properties are eligible for flood coverage though:

RSA noted that for high risk properties, it would be difficult to cover fresh water flooding "because there is almost a guarantee that something is going to happen," she added.

Comment 5) High risk properties can include those in a defined river floodplains. It is reasonable approach that coverage is not available and instead land use policies should deter such high risk developments over time. What is missing in this approach is that governments and their agencies (Conservation Authorities in Ontario) and insurance companies are not managing all risks in a complete and comprehensive way. Will RSA risk zones be shared with municipalities, or with property owners to support land use planning policies or flood proofing efforts by individuals or businesses? Not likely. Or will the sole purpose of the risk maps be to make decisions on the portfolio for the benefit of shareholders - that is likely - there is nothing wrong with that, but if so, let's take a step back and consider what the insurance industry's role really is in terms of managing society's flood risks. Are the efforts by RSA to define flood risk a benefit to society or the balance sheet? Does it make sense that individual insurers redo overland flood risk assessments independently from each other, or should a public flood underwriter make those assessments to be shared by the insurance industry and municipalities? In that manner, there would be no gaps in coverage and risk mitigation strategy.

Comment 6) What is needed to enhance the RSA sub-optimal, incremental improvement to risk pricing for flooding during extreme storms? The answer is a more robust, neighbourhood scale vulnerability model and a comprehensive approach to riverine flood risk. This could result in and mandatory coverage for highest risk overland flood properties as one outcome. Similarly, premiums for backup coverage could be increased in neighbourhoods with high overland flood risk, because clear water entering a few properties and overwhelm the sanitary sewer system in a widespread area. Our research shows how overland flood and backup (basement) flood risks are correlated in this post. Because risks are at a neighbourhood scale and policies are written at a property scale there is no way that the current insurance model can be optimal.

RSA notes in the article that "Canada doesn't have a lot of high risk zones with respect to flood."

Comment 7) In making this statement RSA should have distinguished between urban overland flash flooding and riverine flooding in a valley systems. Certainly a low percentage of properties are within vulnerable valley flood plain areas where rivers and creeks can swell. But on table land, urban flash flooding affects many neighbourhoods built before improved 1980's drainage standard improvements. These table land areas are where 'concurrent causation' really occurs.

Lastly RSA notes "That is going to be very clearly defined as what's covered and not covered"

Comment 8) Costs and revenue may be in a more sustainable balance with the RSA policy updates, but this may not necessarily be because policy coverage is more 'clear' in the future. As noted in the initial comments, there will generally always be some 'brown' mixed into the system when it comes to extreme storms.

Overland Flood Factors Affect Basement Flood Incidents - Correlating Insurance Perils and Mapping Risk

Overland flow risk mapping and basement
flood history highlights risks on table land,
outside river flood plains and traditional hazard
mapping areas.

Flood is the new fire.

Blue is the new red ink, as water damage claims increase. Enough slogans though ... time for insights resulting from new overland risk mapping for the GTA!

Overland flooding had recently becoming an insured peril for residential property owners, offered by Aviva Canada. Others are following suit. So now is the perfect time to explore the differences in "surface flooding" types in an urban environment, to assess risk factors and even look for correlations with traditional insured perils, like sewer back-ups that cause basement flooding. Understanding risk factors can support better decisions and help direct mitigation efforts.

First some set-up and definitions.

Media often reports the devastating flooding in Alberta and Toronto in 2013 in the same breath, but there are important distinctions to be made - High River's "riverine flooding" along the low-lying bottom of a defined valley or wide flood plain is quite different than "urban flooding" high up on the table land (i.e., many thousands of Toronto's flooded homes). To put things in perspective, the Toronto's Don River has a drainage area of 360 sq.km contributing to valley flow, while a table land area subject to urban flooding may have as little as a 0.01 sq.km, or 10 hectare drainage area.

Riverine flooding is largely manageable - spatially fixed, quantifiable in terms of flow frequency and flood depth, and (in Ontario) regulated through the provincial policy statement on natural hazards, MNR guidelines, and conservation authority regulations. In the past, flood plain mapping to define riverine flood risks was once the 'bread and butter' of engineering consultants, who started number-crunching U.S. Army Corps of Engineer's HEC-2 simulation models back using punch cards - yes, that long ago. The limitation is that only a few percent of Ontarians live in flood plains according to Conservation Ontario. And based on new analysis from cityfloodmap.com, only about 2% of May 12, 2000, August 19, 2005, and July 8, 2013 Toronto flooding occurred in river flood vulnerable areas!

Urban flooding, in contrast, affects a greater proportion of the population - 86% of Ontarians live in urban areas per the 2011 census - but this type of flooding is not as readily managed. In fact, risk factors equivalent to flood plain maps are seldom ever mapped. This is because urban flooding is transient and overland flow paths are not permanent physical features that are part of i) a defined valley, or ii) municipal drainage infrastructure. Overland flow paths appear for a few minutes or hours every few decades and then subside. So calling this 'flash flooding' is appropriate - engineering studies show severe urban flooding events are most highly correlated with high short-term rainfall intensities over minutes. Hours later, the overland flow is gone.

To prevent urban flooding, engineers have been designing the overland drainage network though subdivision grading since the early 1980's when "dual drainage design" emerged in Ontario. This approach recognized the limited capacity of the minor system (underground sewer system) for conveniently conveying small storm runoff, and the need to design the major system (above-ground overland system) for extreme storms. In pre-1980 development, the major system still exists but it can run haphazardly beyond roads, through back yards, between houses and into basement windows and walkouts. And this critical, non-designed, transient overland flood risk has not ever been mapped - ta da! - until now.

New analysis from cityfloodmap.com in the slides below ties overland flood risks all together, reviewing flood incidents across regulated valley hazard areas and river flood vulnerable areas (riverine flooding), and within overland flow risk areas across Toronto table lands (urban flooding). It provides insight into risk factors affecting overland flooding and direction on de-risk opportunities. Most importantly, it demonstrates the correlation between traditional sewer back-up peril and the emerging overland peril, which should cause some insurance providers to evaluate portfolio risk (where should coverage be coupled or excluded in isolation, recognizing the correlations).

Urban Flood Risk from Flood Plains to Floor Drains from Robert Muir

If flood is the new fire for the insurance industry, this new analysis, which demonstrates neighbourhood scale flood risk factors due to overland and catchment slope risks, should also prompt discussion on how flood risks are assessed, priced and prioritized for mitigation, adaptation and insurance purposes. Just as fire underwriters identify neighbourhood scale risk factors and consider fire suppression capabilities of municipalities, flood risk assessors should consider the overland risk factors, that extend well beyond the extent of individual properties. Determining risks should not only consider whether an individual property has a reverse slope driveway when broader overland flood risk factors can be readily quantified.

Drought to Deluge - Toward Holistic Flood Risk Management

An online article in Canadian Underwriters describes the new flood risk models developed to assess hazards, price flood endorsements and assess portfolio risk in canadianunderwriters.ca. In the comment below, we look beyond the short term insurance risk data needs and toward to holistic approach risk management.

******

The journey toward a Canada-wide flood risk model shows one thing - a paradigm shift is needed in how the insurance industry, regulatory agencies and municipalities share data on flood risks. Only then will there be data to support fair and accurate insurance products based on risk, data that society can access and use to make important risk management decisions, and data that municipalities/regulatory agencies/ministries can use to set risk avoidance, reduction and remediation policies. The discussion today is just the first step toward that. While a robust 10 m fine grid flood risk screening tool could satisfy the immediate need for price local insurance products and assess portfolio risk, the long term goal has to be a comprehensive risk management strategy built on this type of data. How? Well if "flood is the new fire", consider the fire model where fire underwriters, municipal fire services their consultants, and property owners participate in a system that quantifies and shares risk data and where risk management decisions are made in a coordinated manner.

With immediate product needs, the insurance industry requires a consistent risk model across the country and so has to resort to coarse 30 m topography cell screening to at best identify riverine risks - but can not account for the local factors such as hydraulic relief structures that are important for the higher frequency events (i.e., bridges, culverts and embankment underpasses that are 'under' the 30 m topography model), or the underworkings of sewer infrastructure or surface constraints (building flow obstructions) critical in urban flash flooding beyond river valley systems. Meanwhile, some municipalities are sitting on InfoWorks and EPA SWMM dual-drainage models that predict hydraulic flood levels pipe-by-pipe that characterizes basement flood risk, and predict block by block overland ponding for all storm return periods. Similarly, conservation authorities in Ontario have return period riverine flood levels derived from survey-grade topography and hydraulic structure surveys, considering calibrated flow hydrology. Flood risk data is not new - Toronto East York SWMM models were first developed in the 1970's on punch cards, Toronto North York models in the 1980's on 20MHz 386's - no need for GPU processing really. Today Toronto is covered in InfoWorks models, Hamilton has Mike Urban, Calgary XPSWMM ... and on.

But all this existing data is in silos, each with a single regulatory or management purpose, and never rolled-up, parsed, or aggregated to provide a baseline for insurance risk purposes. You can understand why Carpenter pursues a Canada-wide 30 m grid model for surface flooding or IBC develops MRAT for sanitary back-up risk characterization - its because it is easier to start from scratch with coarse risk assessment than to get down in the weeds of pipe-by-pipe municipal infrastructure flood models (that do vary by neighbourhood to neighbourhood, consultant by consultant, model platform by model platform), or creek-by-creek conservation authority (or other provincial agency) floodplain models (that do vary as well in terms of vintage, accuracy, consistency in hyetographs/design storm drivers). So there has been a deluge of data building for a half century on riverine flood risk, and over decades on urban flood risks - but it has never been approached in a way that it can be leveraged for holistic flood risk management.

Under a new paradigm, with a more holistic risk management end goal in mind, flood risk data can be collected, developed and applied through a partnership approach, without the need to reinvent or duplicate riverine flood risk mapping. Consistent, shared risk data would support alignment between the regulatory aspects of flood risk management, the business decisions related to development, and municipal and government decisions on infrastructure investment and risk reduction programs (flood proofing, emergency preparedness, education). The constraints to getting to there is not GPU computing power for 1 metre-cell 2D urban dual drainage models, but rather it is more fundamental and more challenging, relating to how various private and public organizations cooperatively manage issues of common interest.

Overland Flood Risk - From Flood Plains to Foundation Drains

From foundation drain to floodplain there is a continuum of drainage features that affect flood risks and damages in urban areas - these are micro lot level factors and macro neighbourhood factors.

River flood risks are defined by floodplain maps (called
engineered floodplains) because of the detailed hydrologic
analysis used to define flood flows and river and bridge
surveys used to define river and valley hydraulics to define
precise flood levels. Hazards in these zones are closely
regulated, new development is not permitted, and
redevelopment is subject to special policies if allowed.

Yes, some property reference points could identify a few flood risk factors to address, but overland flooding risk is not apparent at the property scale - that is if we agree overland flooding is not a result of poor lot grading or obvious rain entry points. Unlike other risks like fire hazards, the structure or property does not define most of the risk when if comes to flooding. It will be interesting to see what methods Aviva has adopted for defining risk levels and overland flood endorsement premiums.

Aviva is excluding high risk properties (about 5% of properties) considering flood plain maps that identify river (and sometimes lake) flooding hazards. Micro-scale factors like the property's foundation drain and service lateral condition can affect almost any property, but issues with those do not cause overland / surface water flooding.

Overland flow areas in an urban setting. Areas beyond blue
regulated floodplains may be several hundred hectares in size.

I'd suggest the most sensitive overland flooding occurs upstream of large floodplain-mapped valleys and up onto urbanized 'table land' where the sewer drainage system and overland drainage system are not designed to accommodate runoff from major rainfall events. Usually this would be in catchments draining a 125 hectare or smaller area in Ontario, lying beyond the regulated flood zones above where Aviva insurance would not be available. In these areas, neither the capacity of the storm sewer system, nor the adequacy of the overland drainage system (ideally on roadways and drainage easements) is apparent at the individual property scale.

The macro-scale, overland system is only apparent from runoff accumulation and concentration from 10's of hectares to even a couple hundred hectares of table land runoff that accumulates downstream. That is, a broad neighbourhood-scale macro factor representing many hundreds upstream of properties. The map of overland flow drainage areas (red text in yellow highlight) shows the continuum of drainage areas extending beyond regulated floodplains that flow into to smaller surface features that run through the urban lot fabric.

Engineered floodplain limits are determined through
extensive engineering analysis of the valley system. More
local overland flow limits may be determined through a
local flood remediation study that analyzes the 'major system'
of road drainage as if it is a river valley. That can be
expensive. Alternatively the risk of being close to the
overland flow path can be estimated by defining buffer
distances from small and large runoff area flow paths.

The key overland flood risk factor is whether the property is on the overland flow path where the drainage accumulates. Maybe a property is at a sag in a road where runoff could spill toward the property (i.e., it's vulnerable to overland flooding) but if there is no large upstream area contributing overland runoff toward the property, its not exposed to meaningful risk. But with a large overland drainage area from the neighbourhood flowing into the sag there is a risk to the property. And in that case, disconnected downspouts won't help reduce risk - downspouts drain a couple hundred square meters of rooftop, while large overland catchments can be a couple hundred hectares (meaning 10,000 times greater than the local roof area)

GIS Tools can identify major sags, or depressions,
(called sinks) in the landscape that can indicate or amplify
overland flood risk.

Neighbourhood scale risks factors for overland flooding can be assessed with some minor effort (relative to detailed pipe-by-pipe sewer and street-by-street hydraulic simulation models that is) by just considering topography from readily available elevations models and by applying core GIS hydrology tools.

The image to the left on 'major sags' is an example showing overland flooding risks including dwellings within poorly-drained sags. In this case it includes dwellings upstream of a railway embankment that can impede and 'back up' flows during large events.

Ranked property risk considering proximity to overland flow
path, drainage area, and major sags in topography
(i.e., drainage-challenged during extreme runoff events).

The risk to dwellings and property within close proximity to overland flow paths can be ranked. For example a building within 3 m of a 10 hectare area runoff flow path, or 15 m from 100 hectare area flow path, would be at relatively low risk. Alternatively a dwellings within 3 m of a 100 ha flow path would be at a high risk. A building within both a flow path and in a sag would be at the highest risk. Remember, these are estimates and are qualitative. Nonetheless, experience shows that areas identified through these heuristic methods have be subject to overland flooding during extreme rainfall events.

The issue with overland flood insurance (urban, table-land type flooding) is that risks are concentrated with a small portion of downstream properties for whom risk-based premiums could be unaffordable, or for whom coverage would not be available. The majority of upstream properties would not likely ever experience overland flooding nor add coverage for it. So overland flood damages are not like wind damage (path of wind can be anywhere whereas path of water is always the lowest elevations).

At a property scale, a property with poor lot grading and a reverse slope driveway may be at high risk regardless of proximity to overland flow paths or major sags in topography. Such a property would benefit from having an overland flood endorsement in its water protection insurance. Ideally homeowners in this situation can take action to mitigate risks by improving grading, installing barriers to flow from the reverse drive, keeping grates clear of debris and perhaps installing a backflow valve on the driveway drain. Beyond these exceptions, anyone with foundation drains that could clog or a service lateral that could become root infested is at risk of flooding - but that would not be overland flooding, but rather back-up from the floor drain or seepage from the foundation wall and cracks (a different endorsement all together).

Check out new analysis of table land flood risks and insight into correlations with basement flooding / sewer back-up incidents : overland flow flood risk factors

Identify Flood Risks with the Toronto Flood Map

The Toronto Flood Map can help answer questions for Toronto residents, businesses, tenants, home-buyers, builders, insurance policy holders and insurance brokers / adjusters /actuaries interested in flood risk:

Is a neighbourhood at risk of flooding during severe rain storms? Along what roads or portions of roads have property owners reported flooding during large rainfall events (July 8, 2013, August 19, 2005, May 12, 2000)?
Is the area you are considering buying or renting in flood prone (so does the property of interest have flood risk mitigation measures in place, like a backflow valve to control sewer back-ups, or good lot drainage to keep runoff away from windows, doors and the foundation wall)?

Residents and businesses have reported flood incidents to the City of Toronto after extreme storm events. Calls are made during a flood event or afterward, sometimes as part of an insurance claim related to property damage. The City's map is is shown below.

City's map: Toronto Water Basement Flooding Location Map

As shown on the close up of the City's map below, only major roadways and points of reference are available, making it difficult to pinpoint a local area of interest. Unfortunately the City's map is not at a sufficient scale to show local streets with high historical flooding risk.

Close up of City's map (no local streets shown)

May 2000 locations estimated with symbol (!) on City's map

As a further limitation, May 2000 flood report locations are only shown with a symbol (!) as the original City map did not embed Geographic Information System fonts in the exported PDF file. These symbols are off-set from the reported basement flooding location (red dots in the legend).

Our Toronto Flood Map overcomes City map limitations and reveals high risk areas and neighbourhoods that have flooded during recent severe weather events.

Of course there are limitations in interpreting the flood location map:

The City of Toronto is investing heavily in improvements to the sewer system to limit risks so some areas may no longer have the same risk after construction as they had in the past.

Affected property owners may have invested in individual risk reduction measures (back-flow valves, sump pumps, improved lot grading, etc.) to protect their property from further damage.

Not all flooding is reported so virtually any property along any street could experience flooding under certain conditions. For example, any property could experience flooding if the private sewer or drainage systems on the individual properties are not maintained (clogged foundation drains / weeping tiles, lateral service connection blocked with tree roots or other debris), or if there are other risk factors (reverse slope driveway, etc.). This explains some isolated flood locations.

Because the high intensity area of a storm may cover only part of the city, the density of flood locations reflects the relatively higher local rain stress on the drainage system, and not necessarily the local drainage system capacity compared to other parts of the city. Other storms may affect parts of the City in a greater way (e.g., August 19, 2005 affected the north part of the City, while July 8, 2013 affected the west part).

Individual addresses cannot be identified due to the scale of the map and spatial accuracy.

Nonetheless, Toronto Flood Map can still show the relatively higher flood risk streets within a neighbourhood. Currently the map shows flood reports for the August 19, 2005 and May 12, 2000 storms. The May 12, 2000 basement flooding locations on the City's map have been corrected / adjusted so that affected streets can be identified. The July 8, 2013 storm flood report locations, available through other City reports, will be available shortly as will other historical reports reported through local studies.

Flood Insurance in Canada

Canadian Underwriter highlights two flooding events that are ranked "the most expensive natural catastrophes ever in Canada, prompting insured loss estimates well in excess of $2.5 billion". These events are the southern Alberta flooding and flash flooding in and around Toronto in 2013. Senior executives of reinsurance companies in Canada were polled on what they see ahead for 2014.

On the topic of flooding. Steve Smith President & Chief Executive Officer Farm Mutual Reinsurance Plan noted: “Recognizing that Canada is the only G8 country that does not currently provide some form of flood insurance response, it would appear that the Canadian insurance industry is on the cusp of developing and providing an overland flood cover. If the industry is going to pay the claims anyway, let's develop a workable flood model, clean up the wordings, provide the cover and charge for it.”

By overland flooding he means flooding from rivers or overland drainage systems whereby water enters a property through windows, doors and other openings - not basement flooding from a floor drain, which can have flood insurance, sometimes as an option on a homeowner policy.

It is relatively strait-forward to identify if a property was affected by "riverine" flooding (that is the uninsured kind of flooding). This map shows flood vulnerable areas in the Toronto area. There are numerous locations along major watercourses in Mississauga, Toronto, Markham, Pickering and Ajax.

As an example, lands surrounding Cookville Creek in Mississauga are flood-vulnerable. The flood risk areas are already defined on floodplain maps - these are estimated based engineering simulations of extreme storm runoff and the resulting flow and flood depth through the valley systems.

A 2012 study (Cooksville Creek Flood Evaluation Master Plan EA) identified over 300 properties vulnerable to flooding during the regulatory storm (Hurricane Hazel).

This includes Rhonda Valley properties along the east bank of Cookville Creek shown on the left. The top image is the Google Streetview in sunny weather while the bottom image shows the floodplain extending up onto neighbouring streets on July 8, 2013.

Properties in a floodplain may not be eligible for insurance coverage today because overland flood coverage is not available. It is possible, however, that overland flooding in one neighbourhood contributes to sewer backups in another downstream that does have coverage. This can occur when overland flood water enters homes through windows or walkouts and then enters the wastewater system through basement floor drains. These types of inflows can quickly overwhelm the downstream sanitary sewer causing a mix of diluted sewage and flood water to back up in neighbouring basements.

It is more challenging to identify the overland flood risk beyond valleys where floodplain maps are available. As the following image will show, during the July 8, 2013 extreme rainfall in the Toronto area, flooding was not concentrated along valleys - it was reported on "table land" where runoff overwhelmed the major drainage system (roadways and ditches) and sewers.

Similarly, on August 19, 2005, and on May 20, 2000, flooding in Toronto was also widespread beyond the valley systems (see below). While estimated floodlines are available for some urban areas beyond the valleys, typically a detailed engineering study is required to identify overland flow risks, and these are often evaluated jointly with the sewer system capacity. The Toronto map identifies several of these Environmental Assessment ("EA") project areas.

If the Canadian insurance industry is truly on the cusp of developing and providing an overland flood coverage it will have to consider risk areas. Some risks are already defined through valley floodplain mapping (riverine flooding) while other urban flooding risks on "table land" are not. Tools are available to estimate the urban flooding risk by identifying low-lying areas and those with large drainage areas without a defined major flow route. The analysis can be done quantitatively using a good elevation model and GIS-based hydrology tools and can feed into more quantitative assessments of risk.

British Columbia Floodplain Maps

* See updated Merritt, B.C map link at bottom (Nov. 2021)

British Columbia maintains a comprehensive index of maps showing floodplains, or flood hazard limits / flood areas, throughout the province of BC. These maps illustrate flood risks associated with large river systems as opposed to urban overland flow systems that can cause urban flooding.

The map to the right is an overview of BC flood map areas. Use the links in the list below to find the floodplain map for a particular river, creek, reservoir or lake.

Langley Floodplain Map

To the left is an example of a floodplain map for a particular area - in this case for Langley, B.C. (click to enlarge). Zooming in shows buildings and properties that lie within the flood risk zone. I have spliced together parts of two maps to show an area near the Langley Bypass and Frazer Highway with residential properties within the flood hazard area.

Close-up of buildings in flood risk zone.

Variable river flooding depths for rare event.

The maps show over a hundred buildings within the risk zone. Remember this map shows the limits for a 200-year floodplain - this is the limit of river flooding during a 200-year rainfall event, which is and extreme storm having a chance of occurring of 0.5% every year (1/200%). While this seems rare, if you lived in one of the buildings at the edge of the flood hazard (i.e., right on the floodline), you would have had a 22% change of being flooded over that period. This risk is often misreported by saying you would expect that flood event once in every 200 years (this implies a 100% chance over that period). In fact in 200 years there is only a 63% chance of being flooded.

Th bird's eye view shows some of the variation in flooding depth based on the map's topographic elevations and flood elevations that vary along the river length. You can see that the flood depth varies considerably. The townhomes that have 130 cm of flooding during that flood would have a much higher chance of being flooded during a smaller storm than those with only 10 cm of flooding during the 200 year flood event. Alternatively, for any given storm, the flood damages would be greater the closer the building is to the valley bottom with deeper flooding.

Based on flood risk mapping, do you need flood insurance for your property? Find and insurance broker through the The Insurance Brokers Association of B.C. here.

Here are the links to the available floodplain maps in BC (*update Nov. 2021 - get newest links here: https://www2.gov.bc.ca/gov/content/environment/air-land-water/water/drought-flooding-dikes-dams/integrated-flood-hazard-management/flood-hazard-land-use-management/floodplain-mapping/floodplain-maps-by-region):

A

Alouette and North Alouette Rivers
Drawing No. 89-44 Sheets 1 & 2 - Designation Date 91/09/30

Alpha Lake* (see Whistler Area)
Drawing No. 89-16 Sheets 1 to 4 - Designation Date 93/09/30

Alta Creek* (see Whistler Area)
Drawing No. 89-16 Sheets 1 to 4 - Designation Date 93/09/30

Arrow Reservoir & Kuskanax Creek (Village of Nakusp)
Drawing No. 93-11 Sheet 1 - Designation Date 98/09/30

Region 1 - Vancouver Island

Region 2 - Lower Mainland

Region 3 - Southern Interior

Region 4 - Kootenay

Region 5- Cariboo

Region 6 - SKEENA

Region 7 - Omineca Peace