use of regional climate models for seasonal prediction...
TRANSCRIPT
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Use of Regional Climate Models for Seasonal Prediction
Lessons for Climate Change Application
Liqiang Sun
International Research Institute for Climate and Society (IRI)
Workshop on Evaluating and Improving Regional Climate Projections Toulouse, 11-13 February 2009
with inputs from A. Robertson, L. Goddard, J. Qian, M. Tippett, and K. Baroang
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Seasonal Climate Prediction Using RCMs
• IRI since 1997 • NR&M (Queensland)/IRI 1998 • FUNCEME/IRI since 2001 • CWB/IRI since 2003 • ICPAC/IRI since 2004 • SAWS/IRI 2006, 2007 • ZCC/IRI 2007 • CMC/IRI 2009 • ECPC/NTU,HKO, BIU since 2003 • NCEP since 2002
Challenges Scientific issues related to predictability at smaller scales Technical issues for regional climate modeling Computational constrains
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OUTLINE
Capacity building Predictability of sub-GCM spatial scale climate Challenges in dynamical downscaling of seasonal
prediction and implications for climate projection downscaling
Managing climate variability Recommendations
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Manual for Climate Downscaling Using RCMs
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Observed DJF rainfall: ENSO composite
Sub-GCM spatial scale climate is POTENTIALLY predictable over many regions
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Qian et al. (2006)
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Is Sub-GCM spatial scale climate ACTUALLY predictable?
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Skill comparison between the driving ECHAM forecasts and the nested RSM forecasts. The RPSS (%) was aggregated for the whole Nordeste region.
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Challenges in dynamical downscaling of seasonal prediction
Signal & Uncertainty GCM & RCM Biases Land Process Air-Sea Interaction
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Forecast Mean
Climate Forecast: Signal + Uncertainty
“SIGNAL”
The SIGNAL represents the ‘most likely’ outcome.
The UNCERTAINTY represents internal atmospheric chaos, uncertainties in the boundary conditions, and errors in the models.
“UNCERTAINTY”
Historical distribution Climatological Average
Forecast distribution
Below Normal
Above Normal
Near-Normal
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Optimizing probabilistic information – multi-model ensemble approach
Reliably estimate the uncertainty (for both forcing & response)
Minimize the random model errors
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Downscaling of ECHAM4.5 AGCM Forecast for FMA 2009
RSM RAMS
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CLIMATE DYNAMICAL DOWNSCALING FORECAST SYSTEM FOR NORDESTE
PERSISTED GLOBAL SST ANOMALIES
ECHAM4.5 AGCM (T42) NCAR CAMS
AGCM INITIAL CONDITIONS
UPDATED ENSEMBLES (10+) WITH OBSERVED SSTs
Persisted SSTA ensembles 1 Mo. lead
Predicted SSTA ensembles
1-4 Mo. lead
10
24
Post Processing
RSM97 (60km) RAMS (40km)
CPT
HISTORICAL DATA • Extended Simulations • Observations
PREDICTED SST ANOMALIES Tropical Pacific Ocean (LDEO Dynamical Model) (NCEP Dynamical Model) (NCEP Statistical CA Model) Tropical Altantic Ocean (CPTEC Statistical CCA Model) Tropical Indian Ocean (IRI Statistical CCA Model) Extratropical Oceans (Damped Persistence)
IRI FUNCEME
Sun et al. (2006)
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FMA Precipitation: 1983-1971
50km
~280km 250km
GCM Bias
Sun and Hu (2002)
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RCM Bias
Sun et al. (2005)
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Land initialization
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1. Atmosphere
2. Soil-Plants
4. Groundwater Continents Oceans
Ice Caps 3. Surface Water
?
~ 1-3 m Land Surface
Base of soil model
Present (Regional) climate Models
• Soil water reaching the soil-model base through gravitational flow freely drains out • That water is no longer available for evapotranspiration even during times of water stress
Miguez-Macho et al. (2007)
Land Process Treatment of Groundwater Reservoir in climate models
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Correlations between SST and precipitation for the period MJJA 1979-2006. The areas exceeding the 95% significance level are shaded. Cha and Lee (2009)
Air-sea Interaction
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Managing Climate Variability
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.. crop models need daily time sequences
bridging Climate into Risk Management
.. as do malaria models and hydrologic models
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RSM Hindcast Validation FMAM Rainfal Anomalies
-5 -4 -3 -2 -1 0 1 2 3 4 5
1970 1980 1990 2000
OBS RSM r=0.84
FMAM Drought Index
-200 -150 -100
-50 0
50 100 150 200
1970 1980 1990 2000
OBS RSM r=0.74
FMAM Flooding Index
-20 -15 -10
-5 0 5
10 15 20
1970 1980 1990 2000
OBS RSM r=0.84
FMAM Weather Index
-3 -2 -1 0 1 2 3
1970 1980 1990 2000
OBS RSM r=0.69
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Corn Yield Prediction C
orn
Yie
ld A
nom
aly
(Kg/
ha)
Sun et al. (2007)
Linking prediction and application
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Trend of +10% and no multidecadal variability
Trend of -10% and no multidecadal variability
Reservoir reliability under climate change scenarios
Simulation: single inflow simulation run Reliability: 100 run average Avg Rel: average Reliability over 10 years Baroang & Kaheil
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Recommendations for Downscaling Climate Projections
Use of Multi-model ensemble approach to estimate climate change signal & uncertainty – projection coordination needed
Removal of GCM (systematic) biases to improve RCM performance – more research needed
Application of model output statistics to reduce RCM errors Incorporating water table dynamics into RCMs and land
initialization to better represent land-atmosphere interaction Use of spectral nudging technique to reduce RCM errors Focusing on climate variables that are both relevant and
predictable/projectable (e.g., dry spells, rainfall frequency, monsoon onset) - require creativity to address users’ needs