Disentangling Impacts of Climate & Land Use Changes on the Quantity & Quality of River Flows in Southern Ontario

Transcription

1 Disentangling Impacts of Climate & Land Use Changes on the Quantity & Quality of River Flows in Southern Ontario by Trevor Dickinson & Ramesh Rudra, Water Resources Engineering University of Guelph

2 Acknowledgements Agencies NSERC, OMAF & Environment Canada Personnel Barry Smith - Retired Program Manager, Water Survey of Canada Golmar Golmohammadi Post Doctoral Research Fellow Arezoo Amili Former Graduate Student Akul Bhatt Undergraduate Student Assistant

3 River Flows Have Changed

4 Flow Average Monthly Flow Hydrographs Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall For Rural Watersheds like the Moira River at Foxboro: winter flows have increased, spring flows have decreased, & summer flows have remained unchanged.

5 Flow Average Monthly Flow Hydrographs Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall For a highly Urbanized Watershed like the Don River at Todmorden: winter flows have increased, spring flows have decreased, & summer flows have greatly increased.

6 Monthly & Annual Precipitation has remained unchanged.

7 Average Annual Precipitation (mm) Nith at New Hamburg Grand at Brantford Cedar Creek at Woodstock Moira near Foxboro Linear (Nith at New Hamburg) Linear (Grand at Brantford) Linear (Cedar Creek at Woodstock) Linear (Cedar Creek at Woodstock) Linear (Moira near Foxboro)

8 What s Going On?! Possible causes of changes in the river flows include: - Changes in Climate, and/or - Changes in Land Use i.e. Urban Development

9 How Has Our Climate Changed?

10 Temperatures Have Risen - mostly in the Winter

11 Annual Temperature Trends

12 Changes in Winter Mean Minimum Daily Temperature

13 Annual Temperature Trend Slopes

14 Rates of Increase in Temperatures Celsius degrees per 100 years Extreme Daily Minimum to 4.0 Mean Daily Minimum Mean Daily Mean Daily Maximum Extreme Daily Maximum - 0 to 0.5

15 Temperature Trends So Temperatures have been increasing somewhat steadily in Ontario, - perhaps for up to and at least 150 years! Winter temperatures have been rising at the greatest rate, suggesting that winter hydrology may have been impacted more than summer hydrology.

16 The Frequency of Frost Free Days has Increased Exponentially

17 Number of Frost-Free Days per Winter Frost-Free Days Number of Frost-Free Days versus Mean Daily Minimum Temperature per Winter for 7 Weather Stations days in 60 years days in 60 years day in 60 years WMDMT Winter Mean Daily Minimum Temperature ( C) y = exp(0.1729x) R² =

18 Frost-Free Days As winter mean daily minimum temperatures have been rising steadily, frost-free days have been increasing exponentially. Might snowmelt, which is related to degree-days, also have been increasing exponentially?

19 There Has Been a Shift in Winter Precipitation from Snowfall to Rainfall

20 Changes in Winter Rainfall

21 Changes in Snowfall

22 Changes in Winter Precipitation Total Precipitation Rainfall Snowfall Total Precipitation Snowfall Rainfall Total Precipitation Rainfall Snowfall

23 Increased Winter Temperature Shift from Snowfall to Rainfall (i.e. fewer Snow Days & Less Snowfall, & more Rainy Days & Winter Rainfall) Increased Number of Frost-Free Days

24 What about Impacts on Snowpacks, Winter Runoff & Infiltration

25 Likely Impacts I Rising Winter Temperatures Increased Winter Snowmelt Increasing Number of Frost-Free Days

26 Likely Impacts II Increased Winter Snowmelt Increased Winter Surface Runoff and/or Increased Winter Infiltration Increased Winter Rainfall

27 More Impacts I Increased Winter Tile Flow Increased Winter Infiltration Increased Winter Groundwater Recharge

28 More Impacts II Increased Winter Surface Runoff Increased Winter Streamflow Increased Winter Tile Flow & Recharge

29 And More Increased Winter Snowmelt Decreased End-of-Winter Snowpack Decreased Snowmelt Floods Decreased Snowfall

30 Dec Dec Dec Jan Jan Jan Feb Feb Mar Mar Mar Apr Apr May May May Jun Jun Jun Jul Jul Aug Aug Aug Sep Sep Oct Oct Oct Nov Nov Flow (cms) Flow (cms) Average Daily Flow Hydrographs Winter Spring Summer Fall Moira River at Foxboro

31 Rural Streamflows So for Ontario Rural Watersheds, changes in winter climate have: - increased winter streamflows and - decreased spring runoff/freshettes.

32 Water Quality Impacts What about Water Quality Impacts Are we now seeing more frequent and greater: - Field & Streambank Erosion, - Stream Sediment Loads, and - Nutrient Loads. in rural watersheds during the winter? Have these loads become smaller and less frequent during spring snowmelt events?

33 What about Impacts of Urban Development?

34 Flow For a highly urbanized basin like the Don River, winter flows have increased & spring flows have decreased likely as a result of both Climate Change & Urban Development. In addition, the summer flows have increased significantly in volume Average Monthly Flow Hydrographs Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall

35 Flow (cms) Dec Dec Dec Jan Jan Jan Feb Feb Feb Mar Mar Mar Apr Apr May May May Jun Jun Jun Jul Jul Jul Aug Aug Aug Sep Sep Sep Oct Oct Nov Nov Nov Flow (cms) Average Daily Flow Hydrographs Spring Summer Fall and in frequency on the Don River at Todmorden. What s going on?!

36 Mean event runoff coefficient Runoff Coefficients April May June July August September October Before Urbanization Initial Urbanization Significant Urbanization (50%)

37 Streamflow Volumes So in Ontario urban watersheds: - urban development has augmented the winter and spring climate change impacts; and - summer flow volumes have increased dramatically, in volume and frequency, these impacts being completely due to urban development.

38 Impacts of Urbanization on River Water Quality Are we seeing more frequent flushes and greater volumes of: - streambank erosion - suspended sediment loads - Chlorides and other pollutants - sewage bypasses???

39 Conclusions River flows have changed in Southern Ontario: - in winter and spring, primarily due to climate change; and - during the summer, primarily due to urban development.

40 Questions Water Management Questions What do we do about the changes in river flows - in urbanized and urbanizing watersheds? How have these changes modified water quality, and what do we do in that regard?

41 Questions???

42 Flow Monthly Average Flow Hydrograph Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Moira River at Foxboro

43 Flow Monthly Average Flow Hydrograph Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Winter Spring Summer Fall Don River at Todmorden

44 Dec Dec Dec Jan Jan Jan Feb Feb Mar Mar Mar Apr Apr May May May Jun Jun Jun Jul Jul Aug Aug Aug Sep Sep Oct Oct Oct Nov Nov Flow (cms) Flow (cms) Daily Average Flow Hydrograph Winter Spring Summer Fall Moira River at Foxboro