Changes

Most precipitation events fall into the first category. However, climate change is intensifying storm severity, shifting more events into the second and third categories. One study reported increases in the intensity of 20- and 50-year return period winter precipitation events across the western United States. Another study projected rising intensity of annual maximum precipitation in Canada, with the greatest increases expected in Ontario, the Prairies, and Southern Quebec (Guinard et al., 2015)<ref>Guinard, K., Mailhot, A. and Caya, D. 2015. Projected Changes in Characteristics of Precipitation Spatial Structures over North America. International Journal of Climatology 35 (4):596–612. https://doi.org/10.1002/joc.4006 </ref>. As these storm events grow more frequent and intense, much of our infrastructure faces conditions it was never designed to withstand (Government of Ontario, 2012)<ref>Government of Ontario. 2012. Climate Ready: Ontario’s Adaptation Strategy and Action Plan. Ministry of the Environment, 124p. </ref>. To remain effective, the design of LID features must account for these changing precipitation patterns. Go to [[Understanding rainfall statistics]] to learn more about rain event distributions.

Most precipitation events fall into the first category. However, climate change is intensifying storm severity, shifting more events into the second and third categories. One study reported increases in the intensity of 20- and 50-year return period winter precipitation events across the western United States. Another study projected rising intensity of annual maximum precipitation in Canada, with the greatest increases expected in Ontario, the Prairies, and Southern Quebec (Guinard et al., 2015)<ref>Guinard, K., Mailhot, A. and Caya, D. 2015. Projected Changes in Characteristics of Precipitation Spatial Structures over North America. International Journal of Climatology 35 (4):596–612. https://doi.org/10.1002/joc.4006 </ref>. As these storm events grow more frequent and intense, much of our infrastructure faces conditions it was never designed to withstand (Government of Ontario, 2012)<ref>Government of Ontario. 2012. Climate Ready: Ontario’s Adaptation Strategy and Action Plan. Ministry of the Environment, 124p. </ref>. To remain effective, the design of LID features must account for these changing precipitation patterns. Go to [[Understanding rainfall statistics]] to learn more about rain event distributions.

[[File:Screenshot 2025-09-04 125210.png|900px|center|]]

[[File:Screenshot 2025-09-04 125210.png|900px|center|]]

<small>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)<ref>Toronto Star. 2013. Monday’s storm vs. Hurricane Hazel. 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, GO Train passengers were stranded, and power outages and basement flooding were widespread with property damage of more than $1 billion (Upadhyaya et al., 2014). Hurricane Hazel served as a catalyst for change, revealing the urgent need for an overhaul of flood management practices (TRCA, 2024)<ref>TRCA. 2024. Hurricane Hazel’s Legacy. https://trca.ca/news/hurricane-hazel-70-years/</ref>. Hurricane Hazel was larger than the 100-year design storm (Institute for Catastrophic Loss Reduction, 2000)<ref>Institute for Catastrophic Loss Reduction. 2000. Hurricane Hazel and Extreme Rainfall In Southern Ontario. https://www.iclr.org/wp-content/uploads/PDFS/hurricane-hazel-and-extreme-rainfall-in-southern-ontario.pdf.</ref></small><br>

<small>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)<ref>Toronto Star. 2013. Monday’s storm vs. Hurricane Hazel. 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, GO Train passengers were stranded, and power outages and basement flooding were widespread with property damage of more than $1 billion (Upadhyaya et al., 2014). Hurricane Hazel served as a catalyst for change, revealing the urgent need for an overhaul of flood management practices (TRCA, 2024)<ref>TRCA. 2024. Hurricane Hazel’s Legacy. https://trca.ca/news/hurricane-hazel-70-years/</ref>. Hurricane Hazel was larger than the 100-year design storm (Institute for Catastrophic Loss Reduction, 2000)<ref>Institute for Catastrophic Loss Reduction. 2000. Hurricane Hazel and Extreme Rainfall In Southern Ontario. https://www.iclr.org/wp-content/uploads/PDFS/hurricane-hazel-and-extreme-rainfall-in-southern-ontario.pdf.</ref>.</small><br>

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