Climate changes in Southern Africa; downscaling future (IPCC) projections Olivier Crespo
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Climate changes in Southern Africa; downscaling future (IPCC) projections
Olivier CrespoThanks to M. Tadross
Climate Systems Analysis GroupUniversity of Cape Town
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Historical change
Coherent regional increases in temperature attributable to human emissions
Increase in temperatures ≈ 2°C since 1900 over central southern Africa
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Historical change - rainfall
Observed changes in rainfall:
• Increase in length of dry season and daily rainfall intensity over central region (Kruger, 2006)
• Later onset of rains over eastern lowland regions (Tadross et al., 2005)
• Both the above are observable over parts of southern Africa but very heterogeneous in space and time and the physical mechanisms for the changes are poorly understood
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Future change - scenarios
A1: A world of rapid economic growth and rapid introductions of new and more efficient technologies
A2: A very heterogenous world with an emphasis on familiy values and local traditions
B1: A world of dematerialization and introduction of clean technologies
B2: A world with an emphasis on local solutions to economic and environmental sustainability
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Future change - scenarios
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Future change - temperature
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Regional temperature:
- Historical observed (Black line)
- Historical simulated by 21 global models (Red envelope)
- Projected ranges by 21 global models
red: A2
orange: A1B
blue: B1
Southern Africa projected temperature change at the large scale
Future change
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White areas are where less than two thirds of the models agree in the direction (+/-) of the change
After IPCC AR4: SPM 7
Changes in rainfall from global models
Summer (SH)Summer (SH) Winter (SH)Winter (SH)
Future change
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IPCC AR4 WG1: Ch 1
What are GCMs Good For?
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TemporalResolution
SpatialResolution
GCM nativeresolution
GCM skillor availableresolution
GCM nativeresolution
GCM skillresolution
Point scale inspace and time
Spatialdownscaling
Temporaldownscaling Envelope of coarsest
user resolution
Scales and resolution
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Downscaling
The challenge of bring confident large scale projections to scales of adaptation and policy
Future change
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An empirically derive stochastic or quantitative transfer function conditioned by the large-scale fields from the GCMor
A regional climate model (RCM) nested within the GCM fields
Statistical and RCM downscaling
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Potential changes in rainfall:
• Decreases in winter rainfall over SW Cape
• Increases in summer rainfall over eastern regions
Summer rainfall changeWinter rainfall change
Future change
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JanJan
FebFeb
MarMar
AprApr
MayMay
JunJun
JulJul
AugAug
SepSep
OctOct
NovNov
DecDec
Downscaling to a Downscaling to a 0.10.1º precipitation º precipitation grid:grid:
6 GCMs
SRES A2 forcing
Future – Control anomaly
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