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Uncertainties in Assessing Uncertainties in Assessing Climate Change Impacts on Climate Change Impacts on
California’s Water ResourcesCalifornia’s Water Resources
California Water and Environmental Modeling Forum
February 25, 2004
Jamie Anderson, Ph.D., P.E.
Joint DWR-USBR Climate Change Work Team
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Rose is Rose
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Potential Impacts of Climate ChangePotential Impacts of Climate Change
Precipitation timing and quantity
Runoff timing and quantitySea level rise
Air temperature
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What risks does climate What risks does climate
change pose for the change pose for the
management of management of
California’s California’s
water water
resources? resources?
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Climate Change Work TeamClimate Change Work Team
BG HeilandChris Enright
Aaron Miller Ganesh Pandey
Messele EjetaJamie Anderson
Levi BrekkeSanjaya Seneviratne
Francis Chung
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GOALProvide qualitative and quantitative
estimates of effects of climate change on California’s water resources
Provide information that is relevant to water resources decision makers
including assessment of risks
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Risk = Risk =
f(Hazards, Consequences, Probability)f(Hazards, Consequences, Probability)
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HazardsHazards
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Climate Change HazardsClimate Change Hazards
For this talk, hazards are defined as increments of potential climate change
– Air temperature
– Precipitation
– Sea level rise
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We are relying on climate modelers to forecast possible future climate conditions, and thus assess the hazards of climate change.
Our climate change team currently assesses potential consequences that those climate change scenarios could have on California’s water resources.
Future goal: RISK assessments
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ConsequencesConsequences
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Floods and DroughtsFloods and Droughts
• Rainfall intensity and durations
• Frequency and magnitude of floods and droughts
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Water SupplyWater Supply
• Water Demands human and vegetation
• Inflows to Reservoirs amount and timing
• System Operations size and timing of flood control space; reliability of supplies
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Water QualityWater Quality
• Environmental WQ River and lake temperatures In-stream flow requirements
• Drinking WQ
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San Francisco Bay-DeltaSan Francisco Bay-Delta
• Levee Stability (flooding or sea level rise)
• Sea Water Intrusion
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ProbabilityProbability
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ChallengeGiven the variability and uncertainty in
climate projections over California,
how do we apply climate change impacts assessment to planning and management
of California’s water resources?
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Precipitation
Air Temperature
Divergence in trend and magnitude
Models agree that air temperature increases, but vary in the magnitude and rate of increase
(Source: D. Cayan, April 2003,ISAO Workshop)
Climate Change Predictions for Northern California Differ
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Characterizing Climate Change UncertaintyCharacterizing Climate Change Uncertainty
• Seek advice from other experts
• Develop/apply techniques for quantifying the uncertainty in climate change predictions
• Bookend approach– A lot warmer and wetter– A little bit warmer and drier
• Focus on predictions with least uncertainty– Increase air temperature only– Sea level rise
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Initial Climate Change InvestigationsInitial Climate Change Investigations• Bookend approach
– A lot warmer and wetter (HadCM2 2010-2039 +1.4°C and +26.4% precip)
– A little bit warmer and drier (PCM 2010-2039 +0.4°C and -2.3% precip)
• Focus on predictions with least uncertainty– Increase air temperature only (1.5°C, 3°C, 5°C)– Sea level rise
• Challenge is to assign probabilities to each scenario, e.g. assume that each bookend or sensitivity range is equally likely
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Consequence AssessmentConsequence Assessment
• Bookend and sensitivity analysis approaches provide ranges of consequences for assumed hazards
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Delta Inflow wy1922-1994Delta Inflow wy1922-1994Bookend ApproachBookend Approach
0
500
1000
1500
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2500
3000
3500
4000
4500
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
Flo
w (
TA
F)
PCM 2010 - 2040 2020 Base Conditions HCM 2010 - 2039
Largest range during winter
-200 TAF in Dec
+1,100 TAF in Mar
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Delta Inflow wy1922-1994Delta Inflow wy1922-1994Sensitivity AnalysisSensitivity Analysis
0
500
1000
1500
2000
2500
3000
3500
4000
OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP
Flo
w (
TA
F)
2020 Base Conditions + 3 degrees C + 5 degrees C
Shift in snowmelt and runoff
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Risk AssessmentRisk Assessment
• The bookend and sensitivity analysis approaches provide ranges of consequences for assumed hazards
• Without assuming probabilities for the hazards– Risk assessment has yet to be conducted
– Management choices have not been defined
• Uncertainty analysis is needed
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Climate Change Uncertainty AnalysisClimate Change Uncertainty Analysis
• Develop monthly sensitivity patterns for:– Air temperature – Precipitation– Natural runoff
• Watershed scales (e.g. Oroville, Shasta, etc)
• Evaluated at projection milestones (e.g. 25 years out, 50 years out)
• Account for projection uncertainty:– Patterns from multiple CO2 increase scenarios and/or multiple
GCMs of each CO2 scenario
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Goals of Climate Change Risk AssessmentGoals of Climate Change Risk Assessment• Determine probabilities and potential impacts of
incremental climate change on California’s water resources
• Risk information can be used to: – Develop management plans– Determine priorities in resource allocation– Develop mitigation measures
• Better information on climate change projection uncertainty is needed to conduct this type of risk assessment