EFFECTS OF CLIMATE CHANGE ON STORMWATER MANAGEMENT (SWM) - Gnb.ca

EFFECTS OF CLIMATE CHANGE ON STORMWATER MANAGEMENT (SWM) Hans Arisz, Senior Associate Hydro-Com Technologies a division of R.V. Anderson Associates Limited Fredericton, NB

OUTLINE Introduction SWM Planning & Design Adaptive Options Concluding Remarks

INTRODUCTION Predicting Climatic Change The Challenge

PREDICTING CLIMATE CHANGE Is climate change real? Can we mitigate climate change? Do we need to adapt to climate change? Quantify the timing and magnitude of the effects Two ways to predict climate: Observation of Climate (Trend Analysis) Computer Model Predictions (Global Climate Models (GCMs), Regional Climate Models (RCMs) and Statistical Downscaling)

TREND ANALYSIS SUMMARY More days with precipitation (wet days) Includes rainfall and snowfall Less precipitation on wet days Based on daily data Less annual snowfall Trends in intense precipitation (heavy precipitation days and very wet days) are inconclusive

GLOBAL CLIMATE MODELS Annual average change in precipitation Moncton (CGCM2): 2020 2% 2050 12% 2090 19% Fredericton (CGCM2): 2020 8% 2050 21% 2090 32% Moncton (HADCM3): 2020 8% 2050 6% 2090 8% Fredericton (HADCM3): 2020 -3% 2050 -1% 2090 -3% Source: G. Lines et-al, 2005

GLOBAL CLIMATE MODELS Preliminary predictions for precipitation extremes by J. Wang and X. Zhang, 2007 Computer Model Simulations based on: Increased moisture in the atmosphere (thermal) Increased trigger mechanisms (dynamic) The risk of extreme precipitation increases over almost all of North America The high risk areas are: Southern US, Pacific northwest coast, and Eastern Canada

THE CHALLENGE Wide range of predictions Hydrology tools and guidelines are lacking Predicted over Eastern Canada: Increases in rainfall intensity Precipitation increases 10% to 20% by 2050 What are the effects on stormwater management? How do we accommodate these effects?

SWM PLANNING & DESIGN SWM Planning & Design Dual Drainage Concept Climate Change Effects on Design

SWM PLANNING AND DESIGN Planning The allocation of land and easements to accommodate SWM infrastructure Controlling the interaction between SWM infrastructure and surrounding development Design Determination of the size of SWM infrastructure components required to accommodate design events

DUAL DRAINAGE CONCEPT Dual drainage concept divides the stormwater network into minor and major systems Minor Systems Provides a basic level of service by conveying flows from the more common (minor) rainstorm events Usually consists of the underground pipe network Major Systems Conveys runoff from the extreme (major) rainstorm events Open water channels Includes stormwater storage

CLIMATE ONDesign DESIGN Effects ofCHANGE Climate EFFECTS Change on FLOW HISTORIC 0 5 10 15 20 25 30 35 40 45 50 55 60 65 RETURN PERIOD (Years) 70 75 80 85 90 95 100 105

CLIMATE ONDesign DESIGN Effects ofCHANGE Climate EFFECTS Change on MAJOR SYSTEM DESIGN FLOW FLOW HISTORIC MINOR SYSTEM DESIGN FLOW 0 5 10 15 20 25 30 35 40 45 50 55 60 65 RETURN PERIOD (Years) 70 75 80 85 90 95 100 105

CLIMATE ONDesign DESIGN Effects ofCHANGE Climate EFFECTS Change on 2100 2050 FLOW HISTORIC INCREASE IN FLOW 0 5 10 15 20 25 30 35 40 45 50 55 60 65 RETURN PERIOD (Years) 70 75 80 85 90 95 100 105

CLIMATE ONDesign DESIGN Effects ofCHANGE Climate EFFECTS Change on 2100 2050 FLOW HISTORIC 0 5 10 15 20 25 30 35 40 45 50 55 60 65 RETURN PERIOD (Years) 70 75 80 85 90 95 100 105

CLIMATE ONDesign DESIGN Effects ofCHANGE Climate EFFECTS Change on 2100 2050 FLOW HISTORIC 0 5 10 15 20 25 30 35 40 45 50 55 60 65 RETURN PERIOD (Years) 70 75 80 85 90 95 100 105

CLIMATE CHANGE EFFECTS ON DESIGN The “Bottom Line” for design: Hydrologic data is no longer static over time, i.e. there is no “finish-line” This was the historic basis of design! Flows increase 10% to 20% every 50 years A new SWM design approach is needed!

ADAPTIVE OPTIONS Four Adaptive Options

ADAPTIVE APPROACH # 1 No adjustment to design flows to consider climate change Approach adequate where the incurrence of minor damage associated with flooding is acceptable DESIGN FLOW Design using historic design flows and accept a gradual decrease in the level of service DESIGN CAPACITY NOW END OF SERVICE LIFE TIME “OSTRICH” APPROACH

ADAPTIVE APPROACH # 2 Adjust historic climate record to predict future conditions Hydraulic capacity appropriate for the end of service life Financial burden borne now DESIGN FLOW Design using future design flows (adjust historic design flows) DESIGN CAPACITY NOW END OF SERVICE LIFE TIME “CHICKEN LITTLE” APPROACH

ADAPTIVE APPROACH # 3 Design for flows expected in the shortterm Use shorter design lives to accommodate uncertainty Upgrade costs are likely to be substantial Upgrading minor drainage system is difficult DESIGN FLOW Design infrastructure for shorter service lives, and retrofit or replace when conditions necessitate DESIGN CAPACITY NOW END OF SERVICE LIFE TIME “MULLIGAN” APPROACH

ADAPTIVE APPROACH # 4 DESIGN FLOW DESIGN FLOW Plan and design using a combination of approaches for different drainage components DESIGN CAPACITY DESIGN CAPACITY NOW END OF SERVICE LIFE NOW TIME MINOR SYSTEM APPROACH END OF SERVICE LIFE TIME MAJOR SYSTEM APPROACH Interaction between the minor and major system should be carefully assessed!

CONCLUDING REMARKS Conclusions Recommendations

CONCLUSIONS Climate change is real and unavoidable Increases in precipitation require adaptation Uncertainty in planning and design data Adaptation costs and benefits are unclear SWM and coastal infrastructure appears to be affected most seriously SWM infrastructure may be difficult and costly to upgrade (i.e. urban minor system) “We will have to do: the best we can, with what we have, where we are (in time)”

RECOMMENDATIONS Adopt a flexible and pragmatic design approach, tailored to ease of upgrading Infrastructure Type Stand Alone Integrated Design Approach Importance Design Life High Long Chicken Little High Short Mulligan Low Long Ostrich / Chicken Little Low Short Ostrich / Mulligan High Long Schizo / Chicken Little High Short Schizophrenic Low Long Ostrich / Chicken Little Low Short Ostrich / Mulligan

RECOMMENDATIONS Planning and design for new development Design for the present climate with a moderate allowance for change, but include sufficient flexibility to allow the incorporation of additional capacity, if and when required Planning and design for existing development Designate space for remedial measures when space becomes available through urban redevelopment. Floodproof existing development and infrastructure where possible.

QUESTIONS?

EFFECTS OF CLIMATE CHANGE ON STORMWATER MANAGEMENT (SWM) Hans Arisz, Senior Associate Hydro-Com Technologies a division of R.V. Anderson Associates Limited Fredericton, NB

Design infrastructure for shorter service lives, and retrofit or replace when conditions necessitate Design for flows expected in the short-term Use shorter design lives to accommodate uncertainty Upgrade costs are likely to be substantial Upgrading minor drainage system is difficult TIME DESIGN FLOW END OF SERVICE LIFE NOW