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