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.

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. The Flood Gates Have Opened!
Urban Development has opened
the Flood Gates
– has been a Tipping Point -
for Runoff from Summer Storms !

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. Runoff Probabilities Have Changed
During the Growing Season:
- in Rural Conditions,
P(Runoff) ≈ 0
- in Urban Conditions,
P( Runoff) ► P(Rainfall)

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. Urbanization is a Prime Cause of Flooding
Most flooding reported in southern Ontario
now occurs in urban areas
in the growing season!

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. Questions
???