Climate changes in Southern Africa; downscaling future (IPCC) projections Olivier Crespo
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Transcript of Climate changes in Southern Africa; downscaling future (IPCC) projections Olivier Crespo
Climate changes in Southern Africa; downscaling future (IPCC) projections
Olivier CrespoThanks to M. Tadross
Climate Systems Analysis GroupUniversity of Cape Town
Historical change
Coherent regional increases in temperature attributable to human emissions
Increase in temperatures ≈ 2°C since 1900 over central southern Africa
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
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
Future change - scenarios
Future change - temperature
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
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
IPCC AR4 WG1: Ch 1
What are GCMs Good For?
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
Downscaling
The challenge of bring confident large scale projections to scales of adaptation and policy
Future change
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
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
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