GCM Scenarios for Regional Studies over West Africa

Gregory S. Jenkins

Department of Meteorology

Penn State University

“Africa is Highly Vulnerable to Climate Change.”

IPCC 2001

“Impact of particular concern that are of particular concern to Africa are related to water resources, food production,

human health, desertification and coastal zones especially in relation to extreme events.”

IPCC 2001

“The overall capacity for Africa to adapt to climate change is very

low”

IPCC 2001

A1B scenario

West African Precipitation Anomalies

Objectives of Presentation

• -Compare NCAR CCM3, CCSM v.1 to NCEP

• -Identify Biases in models• Compare 20-21st century climates of West

Africa (5-35N, 20W-40E)• CCM3 (Kiehl et al. 1998) - Climatological

SSTs• CCSM version 1 (Boville and Gent, 1998)

21st century temp./prec. diff

West African Features examined for 20-21st century simulations

• 200 hPa zonal winds- Tropical Easterly Jet- (TEJ)

• 700 hPa zonal winds - African Easterly Jet (AEJ)

• Precipitation field• African Easterly

waves

• Meridional temperature gradient

• Sea Level pressure fields.

Precip. (Observations and CCM)

Precip. (Observations and CCSM)

700 hPa AEJ simulations

African Easterly Waves

• African easterly waves have

• 3-5 day periods (Meridional winds) -Burpee, 1972

• 6-9 day periods - Diedhiou et al. 1999

• AEJ is modulated on similar time periods.

ECMWF/CCSM u,v spectrum

ECMWF/CCSM spectrum of u,v

CCM3/CCSM u,v spectrum

CCM/CCSM/Observational Air Temps.

Sea Level Pressure comparison

Sea Level Pressure Difference

Sahara Warming

Why does the Sahara warm more with elevated GHGs?

• Total warming = increased IR forcing + warm advection (Europe).

• Feedbacks small

• Warming shared between Sahara and Europe!

AEJ, precip, shear linkages

Shear and Precipitation differences (1999-2002)

20-21 century u,v spectrum

Conclusion

• West Africa simulated better in A1 simulations relative to CCM3 but for wrong reasons.

• AEJ, AEWs better simulated in CCSM v.1 • 21st century warming in West Africa uncertain

because of competing factors of warm advection from Europe and land use change in West Africa.

• AEJ frequency shifted to longer timescale in 21st century.

• CCSM v.1 can be used as boundary conditions for regional climate model simulations.

Initial Regional model tests