Potential Impacts of Climate Change on Stormwater

Management

Ed Watt, Mike Hulley & George Zukovs

Presentation Outline• Plausible Scenarios of Climate Change• Stormwater Management – A Brief History• Climate Change – Potential Implications• Key Climate Variables for SWM• Planning & Design Approaches to Mitigate

Adverse Impacts• Conclusion

Plausible Scenarios of Climate Change - IPCC

• Climate change: – natural vs. anthropogenic– Changes atmospheric CO2

• Expected change: the IPCC results– Basis for predictions– Concept of uncertainty– Temperature– Precipitation

Natural Climate Change Ice age cycle (~100,000 years)

20,000 years ago

Atmospheric CO2

Last 20,000 yearsNext 100 years

Intergovernmental Panel on Climate Change “IPCC”

• UN sponsored body formed about 20 years ago.

• Three working groups:– WG1: Scientific Assessment– WG2: Impacts on Natural Environment– WG3: Mitigative and Adaptive Strategies

Temperature Projections• The annual mean warming is likely to exceed the

global mean warming.• Seasonally, warming is likely to be largest in

winter.• Minimum winter temperatures are likely to

increase.

IPCC Likelihood ScaleVery likely > 90% probabilityLikely > 66% probability

Temperature Projections

+/- 5oC

Temperature Projections

Temperature ProjectionsChanges in March Snow Cover

Temperature ProjectionsChanges in Ice Cover: Greenland

Precipitation Projections• Annual mean precipitation is very likely to

increase.• In southern Canada, precipitation is likely to

decrease in summer.• Snow season length and snow depth are very likely

to decrease.• In the northernmost part of Canada maximum

snow depth is likely to increase.

IPCC Likelihood ScaleVery likely > 90% probabilityLikely > 66% probability

Precipitation ProjectionsPrecipitation Intensity

(Annual Precipitation/Number of Wet Days)

Precipitation ProjectionsAverage Number of Dry Days/Year

Basis of Projections?

Plausible Scenarios of Climate Change - IPCC

• Despite relatively large uncertainty for climate change projections:– Large increases in atmospheric CO2 will result (very

likely) in an increase in mean annual temperature.– More intense, less frequent, rainfall events are likely in

the future.– Lower snowpack depths (very likely) will impact

seasonal availability of water.

SWM – A Brief History

• Urban infrastructure & SWM today (& for foreseeable future) reflects approaches over past 100+ years

• Define 4 eras when “the problem”, “solution” and tools varied.

Storm Sewer Era (~1880-1970)

Newark Vancouver (~1900)

SWM Era (~1970-1990)

Cataraqui Pond, Kingston

Urban Stormwater BMP Era (~1990-2007)

Future Eras?• Observation – SWM has not been static &

there is no reason to expect that we have reached the “ultimate solution”

• Emerging approaches– Preservation of the pre-development

water balance– stormwater reuse

Climate Change – Potential Implications

• Sensitivity of SW infrastructure to CC depends on i) magnitude of expected change & ii) type of infrastructure

• Types include– Transmission structures– Management structures for quantity control– Storage structures for quality control– CSO abatement structures

New SWM Infrastructure

• Design pipe diameter will increase with increased design rainfall

• Required live storage of quantity control structures will increase

• Required storage volume of quality control will increase, but design value may not increase (provincial guidelines)

• Size of CSO abatement structures

Maintenance of Existing SWM Infrastructure

• Increase in rainfall severity may force more frequent maintenance for storage structures

• But, maintenance may be relatively insensitive to modest impacts of CC

Retrofit of Existing SWM Infrastructure

• Unlikely that perceived CC alone will lead to significant retrofitting

• However, when retrofitting is planned for any reason, design criteria should be revised to account for the potential impacts of CC

Externalities• Property owners & insurance companies

incur damage costs• Provincial governments fund flood &

erosion control projects• Environmental impacts are

not considered a cost, but rather a fuzzy constraint

• All of these may become more severe

Impacts of Non-climatic Factors

• Deterioration of existing infrastructure• Population growth• New models for financing infrastructure• New provincial standards for SW loadings• New models for SW pricing• Changing public expectation• Evolving public attitudes

Impacts of Non-climatic Factors

• These factors may have impacts of similar or greater impact than climate change

• Need to consider– their evolution – their role in exacerbating or ameliorating

the effects of CC

Planning & Design Approaches to Mitigate Adverse Impacts

• Examine design criteria &methodology• View CC as an additional uncertainty• Relate design criteria to uncertainty• Consider adaptive planning & design

Critically Examine Design Criteria & Methodology

• Design return periods have not changed in many years & may not reflect current or future risk of damage

• In many cases, methodology does not reflect advances in science or best available technology

View Climate Change as an Additional Uncertainty

• Consider potential impacts of CC as one of several uncertainties

• Other uncertainties include future population growth, new standards, new financing models, changing public expectations, evolving attitudes towards the natural environment

+/-

Explicitly Relate Design Criteria to Uncertainty/Risk

• In other civil engineering fields, design criteria are explicitly related to uncertainty, e.g. safety factors

• In stormwater management, design criteria are fixed regardless of uncertainty level

• Why? • Is this appropriate?

Consider Adaptive Planning & Design

• Insofar as possible, maintain flexibility• Facilitate revision of design criteria• Revise plans as design criteria and

methodology evolve• Provide some overcapacity as a hedge

against increased rainfall

Conclusion

• Accept a Non-stationary Climate• Prioritize Relevant Infrastructure

Issues• Review Design Standards• Conduct Risk Analyses