GCM simulations for West Africa: Validation against observations and projections for future

change

G.Jenkins, A.Gaye, A. Kamga, A. Adedoyin, A. Garba, A. Sarr

AF20

NCAR Climate System Model

• Version 1.3 (Gent and Boville, 1998)• Atmosphere 2.8 2.8, 18 vertical levels• Ocean component - variable resolutions 2.3 at the poles,

1.2 at the Equator, 45 vertical levels• Dynamic/thermodynamic Sea ice component• Land surface model (LSM)• Forced by greenhouse gases using starting times of 1870.

Integrated out to 2100 using A1, A2 and B2 scenarios.• CSM has a relatively low climate sensitivity.

Current Status

• 2003- Analysed NCAR Climate System Model (CSM) version 1.3 A1 scenario for West Africa.

• 2004- NCAR CSM simulations of West Africa : Present-day and 21st Century Anthropogenic Climate change, Kamga et al. under review, JGR-Atmospheres

• 2004- Drive the regional climate model with CSM data

• 2004- Will write up RegCM/CSM for publication

Climate Change- Climate Variability linkage in West Africa

• Observed – Reduced Rain rates

associated with:– A southward shift in AEJ

(700 hPa)– A weaker TEJ (200 hpa)– Warmer surface temps.

• Can we use observed changes as a fingerprint for future climate and rain rates?

Reduction in the Area of Lake Chad25000 km2

To 1350 km2

from reduced rainand irrigation

21st Century Regional Climate Change (Temperature)

Understanding Future Climate Change in West Africa

21st Century Regional Climate Change (Precipitation)

Ensemble Model Approach to Climate Change in West Africa

Single Model Approach to Climate Change in West Africa

Single Model Approach to Climate Change in West Africa

21st century temp./prec. diff

Temperature (Observations and CCSM)

Precip. (Observations and CSM)

CSM and Observed annual Precipitation. comparison

CSM and Observed annual Temperature comparison

Observed and simulated Sahelian Precipitation anomalies (20th century)

Observed and simulated Sahelian Temperature anomalies (20th century)

Sahelian 21st temp. trends

Sahelian 21st century Temp. anomalies

Sahelian 21st century precipitation trends

Sahelian 21st century Precipitation anomalies

20th and 21st annual Temp. comparison

20th and 21st annual Precip. comparison

Conclusion

• CSM suggest that the region will become:• Warmer by 1.5-2.5C based on SRES scenarios.• Wetter --especially in the Sahel - due to an

increase in low-level moisture (strengthening of monsoon flow).

• Only small changes noted for Easterly waves.• CSM has significant biases in SLP, Surface air

temperatures, precipitation and 200 hpa Zonal winds.

Future Activities

• Downscaling -- running a regional climate model (RegCM) for present-day and future climates.

• Identifying biases in both GCM and regional climate model simulations.

• Publishing results.• Work to reduce biases in GCM/RegCM.• Will use CSM 2.0 and CSM 3.0 data in the future.• Build human scientific capacity for decades of future

research!!

Future Directions

• Analyze CCSM 2.0/3.0- Biases in Sea level Pressure, upper level winds much smaller.

• Use A1, A2, B2 simulations from new CCSM runs to drive regional climate model.