towards determining ‘reliable’ 21st century precipitation and temperature change signal from...
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Towards determining ‘reliable’ 21st century precipitation and temperature change signal from IPCC CMIP3 climate simulations
Abha Sood
Brett Mullan, Stephen Stuart & Sam DeanClimate Variability Group, NIWA, Wellington
Task:To quantify 21st century regional Precipitation and Temperature climate change signal for end users in agriculture, industry, government, …
Consistency and predictability &
Accuracy and Reliability
Can this be achieved?
Model Credibility
Some problems!!
Start from the beginning!
Change in December-February precipitation (in %), between 1971-2000 and 2071-2099, under an A2 emission scenario
The Experiment
Control ‘Warm’SST forcing, DJF, 1971-2000 (20cL)
‘Warm’ - Control-1.8°C cutoff in SST
-1.7°C cutoff in SST
Results: MSLP
Control ‘Warm’
MSLP Changes , DJF, 21cL-20cL
‘Warm’ - ControlMore blocking More blocking - but not as much as Ctl
Consistency and predictability
. . .
is realized in models based on physical principlesall components of climate system are represented tuning models is restrictedmore advanced model include crucial chemical and biological
processes
Advances are achieved byiteratively improving representation of climate relevant processes in all components of climate models guided by advances in understanding of- climate dynamics, - feedback mechanisms, - representation of climate states for initialization,- drivers of climate change
Accuracy and reliability
. . .
is realized in models byevaluating the ability of reconstructing pertinent features of recent
climate and wide range of past climatesmore information allow probabilistic approach which leads to
decrease in uncertainty and ultimately to ‘narrowing’ of the confidence levels
- advances achieved bysample CMIP3/5 model subset based on model
performance over the region of interest removing known biases in forcing fields (eg SST,SIC) and
in projected climate data
Caution: Future climate may still stray beyond IPCC projection some estimates may be too conservative
Approach:
Multi-Model Ensemble (MME): - more information reduces uncertainties - identification and quantification of modes of internal variability - determine extremes
Model Evaluation and Bias Correction (BC): - ‘realistic’ input for climate impact studies and risk evaluation - helps reveal key model errors
Model Improvement: - remove obvious forcing errors (SST, Sea Ice) - atmosphere ocean coupling at the marginal sea ice zone, - marine boundary layer clouds, - atmospheric chemistry, ♦ ♦ ♦
based onprior
knowledge ofthe system
alsoValidation
and Verification
incomplete informationbased on
limited ensemble
Mullan, Dean (2008)
CMIP3 - IPCC20cL: 1971-200021cN: 2011-204021cM: 2041-207021cL: 2071-2099
•upper and lower bounds, ‘middle of road’ of SRES emission scenarios• multidecadal ocean variability and initial ocean/climate state•perturbations of SST forcing•Selection of CMIP3 models•bias correction of SST forcing
SRES A2 A1B B1
UKMO-HadCM3 x x x
MPI-ECHAM5 x x o
GFDL-CM2.1 x o o
CSIRO-MK3.5 x o o
Regional Climate Model
StatisticalDownscaling
GCM 1
GCM 2
GCM 3
GCM x
Bias-Correction&
Downscaling
Downstream Models:
RiverSnow
Glacier
Climate Change Studies
Climate Change Studies
Climate Change Studies
Regional Modelling & Physical Impacts
Emission Scenarios
Present, Future, Paleo
A2 SST-BC forcing: revised, 20cL DJF
20cL: 1971-200021cL: 2071-2099
Bias correction increases variability and corrects mean
Validation:1972-2000 (VCSN)
DJF JJA
reanalysis driven
A2 SST-BC forcing: revised, 21cL - 20cL DJF
20cL: 1971-200021cL: 2071-2099
BC HadCM3 SST forcing (A2) : rev, DJF
20cL: 1971-200021cN: 2011-204021cM: 2041-207021cL: 2071-2099
21cN - 20cL 21cL - 20cL
21cM - 20cL
Summer Precipitation Change (in %)
BC HadCM3 SST forcing (A2) : rev, DJF
20cL: 1971-200021cN: 2011-204021cM: 2041-207021cL: 2071-2099
21cN - 20cL 21cL - 20cL
21cM - 20cL
Bias corrected Summer Precipitation Change (in %)
A2 SST-BC forcing: rev – ctl, 21cL- 20cL DJF
20cL: 1971-200021cL: 2071-2099
Transient climate change signal: DJF Precipitation
20cL: 1971-2000 21cN: 2011-2040 21cM: 2041-2070 21cL: 2071-2099
revised - control
Transient climate change signal: JJA Precipitation
20cL: 1971-2000 21cN: 2011-2040 21cM: 2041-2070 21cL: 2071-2099
revised - control
Transient climate change signal: JJA Precipitation
20cL: 1971-2000 21cN: 2011-2040 21cM: 2041-2070 21cL: 2071-2099
revised - control
DJF MSLP & Precipitation – 20cL (Observed SST)
Con
trol
obs
erve
d S
ST
Rev
ise
d o
bser
ved
SS
T
DJF MSLP & Precipitation – 20cL (HadCM3 SST)
Had
CM
3 S
ST
Bia
s C
orre
cted
Had
CM
3 S
ST
DJF Southern Annular Mode Index
HadISST + HadCM3 bias corrected HadCM3
MSLP and Precipitation Changes, DJF, 21cL-20cL (MPI)
MSLP and Precipitation Changes, DJF, 21cL-20cL (MIROCM)
ConclusionsRegional climate change over NZ domain is dominated by changes in large scale circulation pattern
Large climate change signal 21st century trend may be nonlinear bias correction reduces signal Trends in temperature increase over time whereas
precipitation may fluctuate
Climate change involves not only changes in mean but also in variability
Reasonably ‘reliable’ climate change signal by bias correcting but is superimposed by large internal variability – low precision
Are there preferred climate states, climate attractors … associated with climate change?
Future Work
Climate model development and improvements
Run more ensemble members; physical and initial state
Projection of the behaviour of climate modes into future considering multi-decadal variability
Improvements in bias correction methodology and initialization concerns
Are there preferred climate states, climate attractors … associated with climate change?
&
Questions?
Summary• Sensitivity in projections of rainfall change - caused by ‘trivially small’ differences in prescribed SSTs
- result in changes in stationary wave patterns & rainfall
- now have a number of GCM/RCM runs that reproduce this instability
• Similar sensitivity present for initial condition ensembles as for parameter/physics ensembles
• Challenges for interpretation of NZ climate changes - a problem with ‘climate scenario paradigm’ - ICs don’t matter!?
- alternatively, maybe 30-year future climatology is too short a period
- nevertheless, there is a climate change ‘signal’
• What now? - explore with further ensemble runs & further analysis
- use a different atmosphere GCM
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