Transcript Exploring the use of Risk Analysis to study the effects of climate

Exploring the use of Risk
Analysis to study the effects of
climate change on CVP and
SWP operations
Levi Brekke (Reclamation, Technical Service Center)
Co-Investigators: J. Anderson (DWR), E. Maurer (Santa Clara University),
and M. Dettinger (USGS, Scripps Institution of Oceanography)
28 February 2007
CWEMF Annual Meeting
Pacific Grove, CA
Acknowledgements
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Reclamation
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R&D Office, Tech Service Center, and Mid-Pacific Region
DWR
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Bay-Delta Office (Modeling Support), Flood Management
USACE
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Sacramento District, ERDC-CRREL
Climate Research Groups
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Scripps Institute of Oceanography (Mike Dettinger)
Santa Clara University (Edwin Maurer)
Lawrence Livermore National Laboratory – Program for
Coupled Model Diagnosis and Intercomparison (PCMDI)
Context
• Reclamation is exploring options in how to
use future climate information in planning.
• This is research on potential methods.
The findings and conclusions of this presentation
have not been formally disseminated by
Reclamation and should not be construed to
represent any agency determination or policy.
Outline
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Analysis Overview:
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Choose scenarios and assess impacts (runoff, operations)
Assess climate projection uncertainty, scenario probabilities
Combine scenarios, impacts and probabilities into risk
Explore strategies to manage risk
Questions Today
1.
2.
3.
How do climate projection distributions depend on
apparent climate model skill?
How do relative climate scenario probabilities depend on
projected variable (e.g., temperature, precip., or both)?
How does operations risk depend on the basis for deriving
relative probabilities for climate scenarios?
Question #1:
How do climate projection
distributions depend on
apparent climate model skill?
Methods
• Premise: Quality of 20th Century Simulation indicates
credibility of 21st Century Projection
• Approach:
– Survey climate simulations, 20th to 21st Century
• 17 models, {20c3m + SRES A2 or B1}
• annual mean T and P during base & 3 future periods
– Evaluate the models’ 20th Century simulation skill
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Get simulated and reference climate variables relevant to Nor. CA
Compute statistical metrics on the monthly values, 1950-1999
Compute metric differences between models and reference
Translate differences into “distances” and then weights
– Construct 21st Century climate change pdfs
• pdf(T), pdf(P), pdf(T,P)
• with and without climate model weighting
Climate Model Weights:
sensitivity to variables & metrics
pdf (Temperature), 3 futures:
sensitivity to model weights
Weighted: based on
different basis
variables and metrics
pdf (T,P), 1 future:
unweighted & weighted
Weighted: based on
“All Variables and
Metrics”
Question #2:
How do relative climate
scenario probabilities depend
on projected variable?
Methods
• Consider 3 variable-specific pdfs, with/without weighting
– pdf(T), pdf(T | “all vars & metrics” climate model weight)
– pdf(P), pdf(P | “all vars & metrics” climate model weight)
– pdf(T,P), pdf(T,P | “all vars & metrics” climate model weight)
• Choose scenarios of interest, locate their projected
climate change values within the pdfs
– E.g., 75 used to fit the pdfs; 22 of those 75 scenarios were
assessed for impacts (discussed later); focus on the 22…
• Scenario probability = ?
– ? point probability density in the pdf
– ? integrated probability within the scenario’s neighborhood with
the pdf, after dividing the pdf accordingly
Relative Scenario Probabilities
(1 future, 6 pdfs, 2 use methods)
Question #3:
How does operations risk
depend on the basis for
deriving climate scenario
probabilities?
Impacts Assessment Methods
(similar to DWR 2006)
• Choose Climate Scenarios (22) and get GCM output
– Downscaled and bias-corrected relative to observed variability
• Simulate Headwater Runoff for base and 2 futures
– NWS CNRFC models, base period 1963-1992
– futures consistent with projected climate (2011-40, 2041-70)
• Simulate Operations for base and 2 futures
– Compute performance metrics on output, by scenario
– Compute changes in future from base, by scenario
• Updated, Dec 2006
• Construct Distributions of Metric Changes (Impacts)
– Resample the distributions proportionately to scenario
probabilities
Runoff Impact:
CVP North, April-July Inflow
Operations Impact:
CVP Delta Exports
Operations Impact:
SWP Delta Exports
Operations Impact:
Lake Shasta Carryover Storage
Questions Revisited
1.
How do climate projection distributions depend on
apparent climate model skill?
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2.
Some effect on local aspects of distribution;
aggregately, not much effect
How do relative climate scenario probabilities depend
on projected variable?
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3.
Significantly, also on how the pdf is used to get probabilities
How does operations risk depend on the basis for
deriving climate scenario probabilities?
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Some effect on local aspects of distribution;
aggregately, not much effect
Next Steps
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Documentation
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Project Report expected Summer 2007
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Brekke, L.D., M.D. Dettinger, E.P. Maurer, M. Anderson, 2006. “Significance of
Model Credibility in Projection Distributions for Regional Hydroclimatological
Impacts of Climate Change”, submitted to Climatic Change, In Review
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Other articles planned…
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Additional Impacts and Risk Analyses
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Delta WQ/Levels, Stream Temps, Power
Risk Management Studies
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Flood Control Rules
Conjunctive Use
Others?