Short Duration Frequent Rainfall Show No Change in Southern Ontario IDF Design Intensities - No Change in Averages Suggests No Change in Extremes

It is often stated that changes in average conditions are an indicator of changes in extreme conditions. This makes sense for rainfall statistics as a change in typical conditions, such as an increase in rainfall intensities, can be accompanied by higher extreme values as well (i.e., the whole distribution shifts). Since extreme values are somewhat elusive to those recording rainfall intensities at Canadian climate stations - that is, they are rare and may not be readily observed in short records or sparsely-spaced climate stations - we can look at the trends in the more abundant and frequent short duration rainfall statistics as an indicator of where the extreme values are heading.

The following table summarizes trends in short duration rainfall intensities for long term Southern Ontario climate stations (below latitude of 44 degrees). Stations have at least 30 years of record. The change in 2-year 5 minute rainfall intensity and 5-year 10 minute rainfall intensity have been calculated using a starting point of then Environment Canada's 1990 IDF tables (obtained from Environment and Climate Change Canada in 2017), and an ending point of the Version 2.3 Engineering Climate Datasets.

Change in average and frequent rainfall intensities in southern Ontario.

The review indicates that there has been no increase in frequent short duration rainfall intensities. In fact the most frequent 2-year (i.e., average), 5-minute duration rainfall intensities have decreased somewhat. This is welcome news considering the potential for frequent storms to cause erosion in southern Ontario streams. This also suggests that extreme rainfall intensities have not changed as a result of the average rainfall intensities changing. That is, there is no consistent shift in the average rainfall intensities at long term climate stations.

The Insurance Bureau of Canada and the Institute for Catastrophic Loss Reduction have reported that average rainfall intensities have shifted by an entire standard deviation (thus making extreme 40 year storms become more frequent 6 year storms) - this has been refuted by Environment and Climate Change Canada (see Canadian Underwriter editor's note). The data in the above table indicate no such shift.

It is a commonly held belief that rainfall intensities have increased dramatically as a result of climate changes effects. Recently the Globe and Mail reported "It is hard to ignore the growing relationship between climate change and the resulting impact of severe flooding events." .. actually its hard to explain the role of changing climate given rainfall intensity data in some regions. It may be best to ignore rainfall and focus on other flood risk drivers like urbanization and intensification.

Datasets from Environment and Climate Change Canada refute the belief that rainfall is becoming more extreme.

***

The following tables show the 2 to 5 year IDF trends for 5 to 10 minutes (first table), and 5 to 10 year trends for 1 hour and 2 hours (second table)

1990 (pre-version 1) IDF Dataset Worksheets have been prepared for Ontario stations:
Ontario Disk 1 Volume Tables :		https://drive.google.com/open?id=0B9bXiDM6h5ViWV9HeXZIWDZxTXM
Ontario Disk 2 Volume Tables :		https://drive.google.com/open?id=1vhaXcC3MidpgHCmSbXdgqy53pUyAXu0g
Ontario Disk 3 Volume Tables :		https://drive.google.com/open? id=0B9bXiDM6h5ViZVpJMEZzWnNDV28
Ontario Disk 4 Volume Tables :		https://drive.google.com/open?id=0B9bXiDM6h5ViZEVoOE8xT0oyZ2M

Less Extreme Short Duration Rainfall in Kitchener-Waterloo - IDF trends do not show climate change impacts that would affect urban flooding.

The University of Waterloo civil and environmental engineering department analyzed design rainfall intensity trends - that is intensity-duration-frequency (IDF) statistics used in infrastructure design - with the goal of potentially updating City of Kitchener and City of Waterloo design rainfall values. Why do this? Because climate change is predicted in some models to increase the intensity and frequency of extreme rainfall. Results are in the following report:

Update of Intensity-Duration-Frequency (IDF) Curves for the City of Waterloo and the City of Kitchener Prepared By: Donald H. Burn, Ph.D., P.Eng. Department of Civil and Environmental Engineering University of Waterloo, August 2012.

The executive summary states there is no significant change and some decreasing trends for short duration rain intensities - that is, the design parameters that affect urban infrastructure flood risks:

"Annual maximum rainfall data for durations ranging from five minutes to 24 hours were analyzed for trends using the Mann-Kendall non-parametric trend test. Although no statistically significant trends were identified, there were noticeable patterns in the magnitude and direction of the trends in the rainfall data, as a function of the rainfall duration. Based on the available rainfall data for the period 1971 to 2007, new intensity-duration-frequency (IDF) curves were developed for the Waterloo Wellington A climate station; the curves can be used as IDF curves for the City of Waterloo and the City of Kitchener. The Pearson Type III (PE3) distribution was identified as the preferred distribution function for the data and formed the basis for estimating the quantiles required to form the IDF curves. The rainfall intensity values for the new IDF curves tend to be lower than the corresponding values for the existing curves for rainfall durations of up to one to two hours and generally slightly higher than the rainfall intensity values for the existing curves for the longer rainfall durations. The results indicate that the existing IDF curves for the City of Waterloo and the City of Kitchener are likely somewhat conservative for rainfall durations less than two hours, although the impacts of climate change could result in more severe events in the future."

The University of Waterloo findings are consistent with the 'general lack of detectable trend signal' in past rainfall observations as reported by Environment and Climate Change Canada (ECCC). ECCC reported even some regional decreasing trends (St. Lawrence region of southern Quebec and the Atlantic Provinces) for the short duration intensities affecting urban drainage systems:

Trends in Canadian Short‐Duration Extreme Rainfall: Including an Intensity–Duration–Frequency Perspective Mark W. Shephard, Eva Mekis, Robert J. Morris, Yang Feng, Xuebin Zhang, Karen Kilcup & show all Pages 398-417, Published online: 19 Nov 2014 (Atmosphere-Ocean).

What do the University of Waterloo findings look like? These intensity-duration curves for 5-year, 25-year and 100-year rain frequencies show that for duration less than 2 hours, the storm severity has been decreasing:

IDF update to assess climate change impacts for sewer design shows decreasing 5-year rainfall intensities for durations less than 120 minutes (2 hours) - small flashy urban drainage systems now have lower extreme rainfall risk than with previously higher rainfall. Therefore earlier designs using older, higher rainfall design intensities have a safety factors against extreme weather risks for frequent events, and climate change has not adversely affected Kitchener-Waterloo erosion risks or erosion damage potential (erosion risks are often governed by frequent storm stresses). 

IDF update to assess climate change impacts for sewer design shows decreasing 25-year rainfall intensities for durations less than 90 minutes (one and a half hours) - small flashy urban drainage systems subject to nuisance flooding now have lower extreme rainfall risks. Therefore earlier storm drainage designs using older, higher rainfall design intensities, have a safety factors against extreme weather risks, and climate change has not adversely affected Kitchener-Waterloo flood risks or damage potential. Wastewater systems that have extraneous flow stresses (i.e., inflow and infiltration) and that respond to short duration rainfall appear to have lower capacity stresses with climate change IDF update. A Class Environmental Assessment Master Plan study in Kitchener has shown that peak wastewater flows in the trunk systems (e.g., Ottawa, Manchester, Montgomery trunks) are most highly correlated to short duration rainfall intensities. A Class Environmental Assessment study of the Sandrock Greenway trunk has also shown that smaller local wastewater systems respond to short duration rainfall intensities, even without high inflow potential in catchments with fully and partially-separated foundation service catchments).

IDF update to assess climate change impacts for sewer design shows decreasing 100-year rainfall intensities for durations less than 90 minutes (one and a half hours) - small flashy urban drainage systems now have lower extreme rainfall risk today compared to previously higher intensities. Therefore earlier designs using older, higher rainfall design intensities have a safety factors against extreme weather risks for rare storm events, and climate change has not adversely affected flood risks or flood damage potential. 

 Why do derived IDF values decrease? Because the observed maximum rainfall amounts in the Annual Maximum Series (AMS) have been decreasing. The following two graphs show trends in annual maximum rainfall recordings from 1971 to 2007. The 5-minute duration maximum rainfall has been decreasing and the 2-hour maximum rainfall have been flat - it is over this range that IDF intensities have been shown to be decreasing n the earlier graphs.

***
Comparing University of Waterloo analysis with politician statements:

Prime Minister Justin Trudeau recently stated "We are a government grounded in science". If so, why has he stated that 100 year storms may occur every 10 years or sooner following 2017 flooding in Gatineau? There is no data to support the storm frequency statement made by the Prime Minister.

Comparing University of Waterloo analysis with insurance industry statements:

The insurance industry, interested in flood damages and the effect on business activities, has stated that storms that happened every 40 years are now occurring every 6 years. Environment and Climate Change Canada has clearly refuted this frequency shift, most recently in Canadian Underwriter saying its studies do not support the insurance industry statement. As noted in the recent article:

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

The following detailed review of insurance industry statement and comparison with Environment and Climate Change Canada's Engineering Climate Datasets clearly shows how the insurance industry has confused projected rainfall intensity shifts with trends from past observations:

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

Lake Ontario 2017 Water Levels Only 4 centimetres Above 1973 Monthly Maximum. But well above average. Lake Deluge Exceeds Leaf Drought !

See May/June 2017 updates at end of this post.

See 2019 review here

***
Some records are made to be broken, whether its the Leaf's Stanley Cup drought or Lake Ontario flooding. At right are the Leaf logos over the years. See the top right logo they had in 1952? And see the current bottom right logo? Old is new again with the logo, right? Same thing with maximum water levels in Lake Ontario.

Back in 1952, from March to June monthly Lake Ontario levels hit records. In 1973 those April and May records were broken .. April 1973 was just 3 cm above May 1952 average, and May 1973 was a measley 1 cm above May 1952. It has taken 44 years to break the spring records again in 2017.

Below are historical average and maximum Lake Ontario water levels from the Departments of Fisheries and Oceans and Environment and Climate Change:

Lake Ontario Historical Water Levels - Average, Maximum and Minimum Monthly Elevations (right y-xis is elevation
above sea level, left y-axis is depth in metres above reference datum of  74.2 metres).

This is from the April 2017 bulletin available here at this link. The historical average, maximum, and minimum monthly values are shown in the table below (see full table here).

On May 28, 2017 the Lake Ontario Level is 1.69 metres above the reference datum elevation of 74.2 metres, meaning an actual water elevation of 74.2 + 1.69 = 75.79 metres above sea level. Hourly levels can be graphed or tabluated from this site. The graph below shows lake levels generally leveling off and rising slightly in the last weeks of May 2017 (y-axis is the depth above the datum):

Real time Lake Ontario water depth above reference datum of 74.2 metres up to May 28, 2017.

Relative to maximum historical values, the May 28, 2017 depth of 75.69 is 4 centimetres above the previous 1973 May monthly maximum of 75.65, and 4 cm below the previous June monthly maximum of 75.73 m. And 75.69 is just 7 centimetres above the 1952 May average. We visited the Outer Harbour Marina yesterday and levels have flooded the fixed perimeter dock / walkway so that temporary paths to the boat slips have been made - so yes, levels are above average and many fixed shore features have been built for the averages and not the maximum levels.

The current Lake Ontario levels are causing a higher erosion potential further inland with waves nearly undermining the boardwalk near Woodbine Beach as shown in this picture:

Beaches boardwalk erosion with above average Lake Ontario water levels 2017.

Gabion baskets (metal wire cages filled with stone), and armour stone (large boulders), are protecting the boardwalk in the Beaches from encroaching lake levels. Further west at Woodbine Beach "Puddlegeddon" is raging on, interfering with volleyball plans although the puddles are subsiding.

Woodbine Beach Puddle-geddon, Puddle-pocolypse, Puddle-o-rama, Puddle-nado, Puddle-duddle ... umm its a puddle and
Lake Ontario levels are a whopping 4 centimetres higher than a previous maximum monthly value.

While you could say water levels are high for volley ballers who have been playing in the Woodbine Beach league for almost 20 years, the levels are only 4 centimetres above the previous May maximum. So it is not unexpected that in a 100 year monitoring record, you exceed an earlier maximum every so often. That is what statistically is supposed to happen with observations of natural systems. Today's Lake Ontario levels are not significantly above the maximum values 65 years ago in 1952 or 44 years ago in 1973.

***
Need up to date Lake Ontario levels 24-7? You can call these numbers to get the current reading, and the maximum and minimum in the past 12 hours. That will include any short term effects from wind set-up (seiches) that tilt the lake higher on one side than another cool. Here are the numbers:

Toronto - (416) 868-6026
Kingston - (613) 544-9264
Burlington - (905) 544-5610
Cobourg - (905) 372-6214
Port Weller - (905) 646-9568

Remember to add 74.2 metres to he number Max Headroom tells you on the phone. He's no Siri or Alexa but you can get the level in English or French.

***
You want more Great Lake real time water level information like the ones above? Call these numbers:

The Canadian Hydrographic Service operates a network of announcing gauges at its stations on the Great Lakes and St. Lawrence River. The following stations can be accessed by telephone at the number listed:

Lake Superior
at Thunder Bay - (807) 344-3141
at Rossport - (807) 824-2250
at Michipicoten - (705) 856-0077
at Gros Cap - (705) 779-2052

St. Marys River
above the lock at Sault Ste Marie - (705) 949-2066
below the lock at Sault Ste Marie - (705) 254-7989

North Channel
Thessalon - (705) 842-2215
at Little Current - (705) 368-3695

Georgian Bay
at Parry Sound - (705) 746-6544
at Midland - (705) 526-6413
at Collingwood - (705) 445-8737

Lake Huron
at Tobermory - (519) 596-2085
at Goderich - (519) 524-8058

St. Clair River
at Point Edward (Sarnia) - (519) 344-0263
at Port Lambton - (519) 677-4092
Detroit River
at Amherstburg - (519) 736-4357

Lake Erie
at Bar Point - (519) 736-7488
at Kingsville - (519) 733-4417
at Erieau - (519) 676-1915
at Port Stanley - (519) 782-3866
at Port Dover - (519) 583-2259
at Port Colborne - (905) 835-2501

Lake Ontario
at Port Weller - (905) 646-9568
at Burlington - (905) 544-5610
at Toronto - (416) 868-6026
at Cobourg - (905) 372-6214
at Kingston - (613) 544-9264

St. Lawrence River
at Brockville - (613) 345-0095
above the lock at Iroquois - (613) 652-4426
below the lock at Iroquois - (613) 652-4839
at Morrisburg - (613) 543-3361
at Cornwall - (613) 930-9373
at Summerstown (Lake St. Francis) - (613) 931-2089

***

Lake Ontario Water Level Update May 2017 

The May water level bulletin in out at this link. It shows we finally broke the record for maximum recorded Lake Ontario water level for May (see chart below). As of May 10 there was no record breaking - as noted in the Environment and Climate Change Canada LEVELnews:

"By the end of April, Lake Ontario had risen to levels that haven’t been seen since 1993, and reached near record levels in the first week of May. By May 10 the daily average Lake Ontario water level was 75.80 m, only 2 cm below the highest level ever recorded (1918–2016) at the beginning of June 1952."

Lake Ontario Water Level

Near Woodbine Beach in Toronto's Beaches neighbourhood, the shore erosion has caused the boardwalk to now be fenced-off. Beyond the armour stone, gabion basket and rip rap revetement that has protected some portions of the boardwalk, the shore has washed away and the boardwalk is undermined, suspended and sagging, hence the barriers:

It makes you wonder what is more effective and reliable, the grey infrastructure in the distance (conventional Armour Stone, gabion baskets (not visible below the surface stones), "rip rap" limestone, or the softer treatment of green infrastructure soil and roots in the foreground that has all washed away due to the force of high water and waves. Basically, the boardwalk damage happened beyond where the conventional grey infrastructure ended, where the green infrastructure failed. This experience suggests that old-fashioned grey infrastructure is more reliable and effective at erosion protection than softer revetment. Certainly the green part of the shore was robust for low lake levels and erosion forces, but not strong enough for above average conditions like we see in Spring 2017 on Lake Ontario.

******

June 24, 2017 Update:

The erosion damage restoration (two layers of armour stone) has been installed along the boardwalk and will provide future erosion protection ... because water level records are made to be broken.

And further west Woodbine Beach has been drying up, and volleyball has returned to larger areas (in the background) now that Lake Ontario water levels are returning to their normal lower elevations. But there is still some evidence of spring 2017 Puddlegeddon.

***

For and updated review of historical Lake Ontario water levels see this new post that explores Toronto Island storms and flooding.