Regional rainfall variability over Central Africa:

1. Regional rainfall variability over Central Africa: What is influencing it?

2. Aims and Motivation: • Investigate the overriding mechanisms responsible rainfall over central Africa. • Understand the cause of interannual/interdecadalvariability during the rainy season(s). Also, to asses the impacts of Teleconnections over the region. • Investigate the sensitivity of the Central Africa region to future climate and land use change through the use of differing scenario’s in a regional climate model. • Increased understanding of the overriding mechanisms responsible for variations in rainfall for forecasters. Background: • Central Africa roughly covers 2.6% of the Earth’s surface with an estimated population of around 120 million people, which is expected to rise to and estimated 250 million by 2050. • The countries of central Africa rely economically upon rain-fed agriculture for the majority of their livelihood(mainly subsidence based). • Land use change, particularly from deforestation may play a vital role in the future climate of the region dictated by increasing population pressures.

3. Processes of influence: • MCS/Squall lines • The Inter-tropical Convergence Zone (ITCZ) • Sea Surface Temperatures (SSTs) • Regional African Jets: • African Easterly Jet-North (AEJ-N) • African Easterly Jet-South (AEJ-S) • Tropical Easterly Jet (TEJ) • Westerly African Jet (WAJ) • Role of the vegetation? • Teleconnections? • EL-Nino Southern Oscillation (ENSO) • Large-scale circulations (Hadley and Walker circulations) Dry Wet

4. Rainbelt: 15°N 0° EQ Variability in rainfall linked to variability in Intensity and position. 15°S Variability in the rainbelt for August From Nicholson, 2008 and 2009.

5. Methodology: • Data Sources: • Rain gauge network • NCEP-NCAR reanalysis • ERA-40 reanalysis • Regionalisation: • Based upon seasonal rainfall cycle • Composite Analysis: • Time series • 5-driest years of the wet season(s) • 5-wettest years of the wet season(s) • Cross validation approach

6. Example - Region B: MAM Composites Wet Dry OLR SST

7. Wet Dry Tropical SSTs 200mb Vectors

8. Region B: SON Composites Wet Dry SSTs Tropical SSTs

9. Wet Dry SLP In short: A complex relationship exists where a combination of differing regional and global scale processes can influence the rainfall over central Africa. It is thus imperative to better understand how these processes work and how future climate and regional land use change in central Africa impact them and rainfall.

12. Preferable area for large-scale, organised, deep convection TEJ 200mb AEJ-S AEJ-N 500mb Seasonal rainfall (mm) Preferable area for shallow convection WAJ 1000mb EQ 20ᵒS 20ᵒN Schematic depicting a favourable jet configuration for enhanced rainfall over central Africa (note: Example shown for when the AEJ-S is present).

13. Preferable area for large-scale, organised, deep convection TEJ 200mb ? AEJ-S AEJ-N 500mb Seasonal rainfall (mm) Preferable area for shallow convection WAJ 1000mb EQ 20ᵒS 20ᵒN Schematic depicting an unfavourable jet configuration for enhanced rainfall over central Africa (note: Example shown for when the AEJ-S is present). ? – Highly localised enhanced rainfall?

14. Modelling: • HadAM3 • PRECIS • HadAM3– for resolution test (regional-scale variability) Uses of models: • Control run comparison with observation and reanalysis data. Test hypothesis’s on what controls variability in the region. • Sensitivity studies – land cover /future climate experiments – What role does the land surface play?

15. NCEP minus PRECIS model example: JJA

16. NCEP minus PRECIS model example: JJA

17. NCEP vs. ERA40A comparison of reanalysis data over central Africa.

18. Region B MAM: ERA NCEP

19. Region B: ERA NCEP

20. Region B MAM: ERA NCEP

21. Region B: ERA NCEP

22. Region B: ERA NCEP

23. Future work: • HadAM3 run - Climatology run, how well does it compare theories • TAMSAT analysis/validation of region • Land cover change sensitivity experiments • Climate change sensitivity experiments.