Changes

'''Climate-Related Impacts'''

'''Climate-Related Impacts'''

Since 1995, Ontario has had a weather-related state of emergency almost every single year <ref>Swiss Re (in collaboration with Institute for Catastrophic Loss Reduction) (2010). Making Flood Insurable for Canadian Homeowners. Available at URL: http://www.iclr.org/images/Making_Flood_Insurable_for_Canada.pdf</ref>. The City of Windsor saw extreme events that caused severe flooding in 2007, 2010, 2016 and 2017 <ref>City of Windsor. 2012. Climate Change Adaptation Plan. Available at URL: http://www.citywindsor.ca/residents/environment/environmental-master-plan/documents/windsor%20climate%20change%20adaptation%20plan.pdf</ref>. The Ottawa region experienced one extreme event every year for five years, and in the Greater Toronto Area (GTA), there have been four extreme rainfall events in the past ten years (Environment Canada, 2014). Such high intensity events produce heavy rainfall in relatively short periods of time. While it is reasonable to expect runoff to be produced under such conditions – particularly when rain falls which exceeds a soil’s hydraulic conductivity - the production of stormwater is exacerbated in urban areas where the overwhelming majority of surfaces are impervious. The problems associated with managing stormwater volumes are exacerbated when dense stormsewer networks efficiently convey stormwater runoff volumes from a large contributing upland area to a single outlet location, such as a stormsewer outfall in a river or stream.

Since 1995, Ontario has had a weather-related state of emergency almost every single year <ref>Swiss Re (in collaboration with Institute for Catastrophic Loss Reduction) (2010). Making Flood Insurable for Canadian Homeowners. Available at URL: http://www.iclr.org/images/Making_Flood_Insurable_for_Canada.pdf</ref>. The City of Windsor saw extreme events that caused severe flooding in 2007, 2010, 2016 and 2017 <ref>City of Windsor. 2012. Climate Change Adaptation Plan. Available at URL: http://www.citywindsor.ca/residents/environment/environmental-master-plan/documents/windsor%20climate%20change%20adaptation%20plan.pdf</ref>. The Ottawa region experienced one extreme event every year for five years, and in the Greater Toronto Area (GTA), there have been four extreme rainfall events in the past ten years <ref>Environment Canada. 2014. Climate. Available at URL: http://climate.weather.gc.ca/</ref>. Such high intensity events produce heavy rainfall in relatively short periods of time. While it is reasonable to expect runoff to be produced under such conditions – particularly when rain falls which exceeds a soil’s hydraulic conductivity - the production of stormwater is exacerbated in urban areas where the overwhelming majority of surfaces are impervious. The problems associated with managing stormwater volumes are exacerbated when dense stormsewer networks efficiently convey stormwater runoff volumes from a large contributing upland area to a single outlet location, such as a stormsewer outfall in a river or stream.

In July 2013, the GTA experienced its most severe storm event in 60 years. Nearly five inches (126 mm) of rain fell in a two-hour period. In comparison, during Hurricane Hazel (a devastating event in 1954 where 81 lives were lost), the two-hour maximum precipitation was 91 mm and the total amount of rainfall was 285 mm over nearly two days (Toronto Star, 2013). Conventional municipal drainage systems could not carry stormwater away fast enough. Roads and highways were overcome with floodwater closing major transportation corridors including Highway 427. GO Train passengers were stranded, and power outages and basement flooding were widespread with property damage of more than $1 billion <ref>Insurance Bureau of Canada (IBC). 2016. Facts of the property & casualty insurance industry in Canada. 36th edition, ISSN 1197 3404. Available at URL: http://assets.ibc.ca/Documents/Facts%20Book/Facts_Book/2016/Facts-Book-2016.pdf</ref>.

In July 2013, the GTA experienced its most severe storm event in 60 years. Nearly five inches (126 mm) of rain fell in a two-hour period. In comparison, during Hurricane Hazel (a devastating event in 1954 where 81 lives were lost), the two-hour maximum precipitation was 91 mm and the total amount of rainfall was 285 mm over nearly two days <ref>Toronto Star. 2013. Monday’s storm vs. Hurricane Hazel. Available at URL: http://www.thestar.com/opinion/letters_ to_the_editors/2013/07/14/mondays_storm_vs_hurricane_hazel.html</ref>. Conventional municipal drainage systems could not carry stormwater away fast enough. Roads and highways were overcome with floodwater closing major transportation corridors including Highway 427. GO Train passengers were stranded, and power outages and basement flooding were widespread with property damage of more than $1 billion <ref>Insurance Bureau of Canada (IBC). 2016. Facts of the property & casualty insurance industry in Canada. 36th edition, ISSN 1197 3404. Available at URL: http://assets.ibc.ca/Documents/Facts%20Book/Facts_Book/2016/Facts-Book-2016.pdf</ref>.

While it is nearly impossible to ascribe the cause of a single event to the broader issue of climate change, the trend is clear: an increasing number of high-intensity, short-duration (HISD) events are impacting our urban areas, exacerbating the stresses on overtaxed stormwater infrastructure. The figure below highlights a series of seven recent extreme rainfall events which have struck the Greater Toronto and Hamilton Area (GTHA).   

While it is nearly impossible to ascribe the cause of a single event to the broader issue of climate change, the trend is clear: an increasing number of high-intensity, short-duration (HISD) events are impacting our urban areas, exacerbating the stresses on overtaxed stormwater infrastructure. The figure below highlights a series of seven recent extreme rainfall events which have struck the Greater Toronto and Hamilton Area (GTHA).   

INSERT PHOTO

INSERT PHOTO

Typically designed to handle the smaller, most frequent storm events, LID practices in Southern Ontario are usually sized according to the 90th percentile event (see figure below). In the GTA, this translates into events that are approximately 25 mm or less in size.  Note that 25 mm is also considered to be a suitable representation of the ‘first flush’ volume, and that controlling this amount of runoff provides stormwater engineers with control over 90% of the mean annual pollutant load (Pitt, 1999).

Typically designed to handle the smaller, most frequent storm events, LID practices in Southern Ontario are usually sized according to the 90th percentile event (see figure below). In the GTA, this translates into events that are approximately 25 mm or less in size.  Note that 25 mm is also considered to be a suitable representation of the ‘first flush’ volume, and that controlling this amount of runoff provides stormwater engineers with control over 90% of the mean annual pollutant load <ref>Pitt, R. 1999.  Small Storm Hydrology and Why it is Important for the Design of Stormwater Control Practices. In: Advances in Modeling the Management of Stormwater Impacts, Volume 7. Computational Hydraulics International, Guelph, Ontario and Lewis Publishers/CRC Press. 1999</ref>.

INSERT PHOTO

INSERT PHOTO

References:

References:

Bäckstrom, M.; Karlsson, S.; Bäckman, L.; Folkeson, L.; Lind, B.  2004.  Mobilisation of Heavy Metals by De-icing Salts in a Roadside Environment.  Water Research, 38:720-732.

Bäckstrom, M.; Karlsson, S.; Bäckman, L.; Folkeson, L.; Lind, B.  2004.  Mobilisation of Heavy Metals by De-icing Salts in a Roadside Environment.  Water Research, 38:720-732.