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Climate Change & Urban Development Have Impacted Streamflows in Southern Ontario

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Dr. Trevor Dickinson, Professor Emeritus University of Guelph presented his work with Ramesh Rudra and Kishor Panjabi, Water Resources Engineering, University of Guelph to the Southern Ontario Stormwater Discussion Group at its September 27, 2018 meeting in Brantford, Ontario. The presentation shows the effects of climate on streamflows in southern Ontario including lower spring flow volumes and rates, and the effects of urbanization on streamflows including higher spring and summer flows. The distribution of flooding events through the years is reviewed, showing fewer spring and more summer period flood events. Climate change appears to increase winter runoff volumes due to higher temperatures which reduce spring volumes and peaks, a decrease in flood risk.

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Climate Change & Urban Development Have Impacted Streamflows in Southern Ontario

  1. 1. Climate Change & Urban Development Have Impacted Stream Flows in Southern Ontario by Trevor Dickinson, Ramesh Rudra & Kishor Panjabi Water Resources Engineering University of Guelph
  2. 2. Acknowledgements  Agencies  NSERC, OMAF, Env. Can., Conservation Authorities & Water Survey of Canada  Personnel  Barry Smith & Other Professional Colleagues  Post-Doctoral Research Fellows  Amanda Siwik & Past Graduate & Undergraduate Student Assistants
  3. 3. 0 20 40 60 80 100 120 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow 1916-1925 0 20 40 60 80 100 120 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow 2004-2013 Rural River Flows Have Changed For Rural Watersheds like the Moira River at Foxboro: winter flows have increased, spring flows have decreased, & summer flows have remained unchanged.
  4. 4. 0 1 2 3 4 5 6 7 8 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow 2004-2013 0 1 2 3 4 5 6 7 8 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow 1916-19251963-1972 Urban River Flows Have Changed For a highly Urbanized Watershed like the Don River at Todmorden: winter flows have increased, spring flows have decreased, & summer flows have greatly increased in volume.
  5. 5. 0 20 40 60 80 100 120 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow(m3/s) 1916-1925 2004-2013 Rural Versus Urban River Flow Changes 0 1 2 3 4 5 6 7 8 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow(m3/s) 1916-19251963-1972 2004-2013 Rural river flows Urban river flows
  6. 6. Changes in Monthly Distribution of Reported Floods 0 10 20 30 40 50 Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec %ofEvents Month Flood Events (1950 to 1975) 0 10 20 30 40 50 Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec %ofEvents Month Flood Events (1975 to 2000)
  7. 7. Changes in Winter Hydrology in Ontario Winter Rainfall Winter Surface Runoff Springmelt Infiltration Springmelt Tile Flow Winter Temperature Frost-Free Days Snowfall Winter Infiltration Winter Tile Flow Winter Streamflow Winter Snowmelt End of Winter Snowpack Spring Runoff Springmelt Streamflow and/or and/or Variable has increased Variable has decreased Data Available
  8. 8. Impacts of Winter & Spring Changes In southern Ontario: 1. Winter flows have increased, and perhaps winter floods are becoming more likely. 2. Spring flows and floods have decreased. 3. Reservoir filling and management have become more difficult. 4. The timing and volumes of water quality discharges have likely changed.
  9. 9. 0 20 40 60 80 100 120 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow(m3/s) 1916-1925 2004-2013 What About the Changes in Urban Summer Flows? 0 1 2 3 4 5 6 7 8 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Flow(m3/s) 1916-19251963-1972 2004-2013 Rural river flows Urban river flows
  10. 10. Possible Conclusions & The Evidence One could conclude that: - we are experiencing many more rain events, and/or much more severe rain events. In fact: - the number of rainfall events has not increased, - the total amount of rainfall occurring over the growing season has not increased, & - to date, there is no evidence that rain storms are more severe.
  11. 11. Changes in % of Rainfall Events Generating Rural Runoff Rural conditions Events > 3mm rainfall 𝐑𝐮𝐧𝐨𝐟𝐟 𝐂𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭 > 0.05 0 20 40 60 80 100 Mar Apr May Jun Jul Aug Sep Oct Nov %ofRainfallEventsGeneratingRunoff Month Moira 1921-30 Moira 1963-72 Moira 2006-15
  12. 12. Changes in % of Rainfall Events Generating Urban Runoff Urban conditions Events > 3mm rainfall 𝐑𝐮𝐧𝐨𝐟𝐟 𝐂𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭 > 0.05 0 20 40 60 80 100 Mar Apr May Jun Jul Aug Sep Oct Nov %ofRainfallEventsGeneratingRunoff Month Moira 1921-30 Don 1963-72 Don 2006-15
  13. 13. Frequency of Runoff from Highly Urbanized Areas There are 15 Times more runoff events in the Don River than in rural watersheds during the growing season.
  14. 14. Changes in Upper Decile 𝐑𝐮𝐫𝐚𝐥 𝐑𝐮𝐧𝐨𝐟𝐟 𝐂𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭𝐬 Rural conditions 0.0 0.2 0.4 0.6 0.8 1.0 Mar Apr May Jun Jul Aug Sep Oct Nov RunoffCoefficient Month Moira 1921-30 Moira 1963-72 Moira 2006-15
  15. 15. Changes in Upper Decile 𝐔𝐫𝐛𝐚𝐧 𝐑𝐮𝐧𝐨𝐟𝐟 𝐂𝐨𝐞𝐟𝐟𝐢𝐜𝐢𝐞𝐧𝐭s Urban conditions 0.0 0.2 0.4 0.6 0.8 1.0 Mar Apr May Jun Jul Aug Sep Oct Nov RunoffCoefficient Month Moira 1921-30 Don 1963-72 Don 2006-15
  16. 16. Urban Runoff as a % of Rainfall The percentage of rainfall that runs off during the largest runoff events during the growing season is 10 Times Greater in the Don River than in rural watersheds.
  17. 17. Rainfall versus Runoff So … whereas the number of summer rain events has not increased, the number of summer runoff events in urban areas has greatly increased; and whereas the amount and severity of summer rainfall events have not increased, the volume and rate of summer runoff and stream flows in urban areas like the Don River have greatly increased.
  18. 18. The Flood Gates Have Opened! Urban Development has opened the Flood Gates – has been a Tipping Point - for Runoff from Summer Storms !
  19. 19. The Summer Season of Urban Floods Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Rural Watersheds + Climate Change Urban Watersheds + Climate Change Rural Watersheds
  20. 20. Runoff Probabilities Have Changed During the Growing Season: - in Rural Conditions, P(Runoff) ≈ 0 - in Urban Conditions, P( Runoff) ► P(Rainfall)
  21. 21. Impacts of Changes in Urban Summer Flow In Urbanized Areas: 1. Localized and downstream flooding have become more likely in summer months. 2. Streambank and streambed erosion have become much more widespread and severe. 3. Water quality discharges have likely changed considerably.
  22. 22. Urbanization is a Prime Cause of Flooding Most flooding reported in southern Ontario now occurs in urban areas in the growing season!
  23. 23. What now? 1. Plan for local as well as river flooding. 2. Address the questions: How much of southern Ontario do we plan to pave? or How can we preserve, protect & incorporate Green Space into ongoing & future development plans? 3. Remain alert to known and anticipated changes in climate. 4. Explore possible impacts on water quality and other environmental conditions.
  24. 24. Questions ???

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