FIELD-DEMONSTRATED EVIDENCE OF CHANGING RAINFALL INTENSITIES IN ONTARIO FOR SHORT DURATION STORMS

B. Vasiljevic, E. McBean, and R. RudraUniversity of GuelphGuelph, Ontario, Canada

Designs for sewers, culverts, and stormwater management ponds rely upon the intensity-duration-frequency (IDF) curves

Stormwater facilities intended to last for decades

Implications also for water supplies

Wells become submergedImplication of rainfall intensity is clear

and profound

Duration

mm

I(mm/hr) I(mm/hr) I(mm/hr)

2 YR

1970-1984

2 YR

1985-2003

5 YR

1970-1984

5 121.4 136.5 135.3

10 80.4 99.5 94.0

15 66.1 81.5 72.9

30 43.8 55.7 51.5

60 25.3 34.6 33.0

120 15.8 19.8 20.8

360 6.8 7.6 8.9

720 3.8 4.3 4.9

IDF Curves Waterloo 5 Year Recurrence Interval

0

20

40

60

80

100

120

140

160

0 30 60 90 120Duration (min)

I (mm/hr)

Existing Waterloo Curve

PDS (70 - 84)

PDS (85 - 03)

Annual Percentage Change in Storm Intensity for a 5-Year Event - Southern Ontario Stations

-1.00

0.00

1.00

2.00

3.00

4.00

30 60 120 360

Storm Duration (min)

Ch

ang

e p

er Y

ear

(%)

Delhi

Port Colborne

Preston

Sarnia

Waterloo

Annual Percentage Change in Storm Intensity for a 5-Year Event - Northern Ontario Stations

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

30 60 120 360

Storm Duration (min)

Ch

ang

e p

er Y

ear

(%)

Chalk River

Sudbury

Timmins

Annual Percentage Change in Storm Intensity for a 5-Year Event - Central Ontario Stations

-1.00

0.00

1.00

2.00

3.00

30 60 120 360

Storm Duration (min)

Ch

ang

e p

er Y

ear

(%)

Bowmanville

Burketon

Kingston

Orillia

Oshawa

IDF curves Waterloo 5 year recurrence interval

0

20

40

60

80

100

120

140

160

0 30 60 90 120Duration (min)

I (mm/hr)

Existing Waterloo Curve

PDS (70 - 84)

PDS (85 - 03)

Interpretation of Trends in Precipitation Increases in precipitation intensity are

occurring throughout Ontario The changes of rainfall intensities in

southern Ontario are more profound, but substantial regardless For example, there is evidence of the five-year storm

increasing at 2% per year in Waterloo so in thirty years, this

translates to a sixty percent increase in precipitation intensity in thirty years in Waterloo if these trends continue

Design features for water infrastructure must be modified, to reflect the changes in intensity that are being observed.

Street From ToPipe Size ( mm)

2 3

(South)

MH1 MH2 300 300

MH2 CBMH3 300 300

CBMH3 MH4 375 375

MH4 CBMH5 600 675

CBMH5 #1 750 750

#1 WETLAND 750 825

(North)

FUT MH11 300 300

MH11 CBMH12 375 375

CBMH12 DCBMH13 450 525

DCBMH13 MH8 600 675

MH8 #2 600 600

#2 FOREBAY 600 675

Conclusions

There is evidence that rainfall intensities are changing, since the five year storm of four decades ago is now the two year recurrence interval storm, and hence translates to implications for design of urban infrastructure.

Implications to water supply systems are highly relevant

Questions?