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

Aims and Motivation: Investigate the overriding mechanisms responsible rainfall over central Africa. Understand the cause of interannual/interdecadal variability 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 scenarios 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 Earths surface with an estimated population of around 120 million people, which is expected to rise to and estimated 250 million by 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.

Processes of influence: MCS/Squall lines The Inter-tropical Convergence Zone (ITCZ) Sea Surface Temperatures (SSTs) Regional African Jets: 1.African Easterly Jet-North (AEJ-N) 2.African Easterly Jet-South (AEJ-S) 3.Tropical Easterly Jet (TEJ) 4.Westerly African Jet (WAJ) Role of the vegetation? Teleconnections? EL-Nino Southern Oscillation (ENSO) Large-scale circulations (Hadley and Walker circulations) Dry Wet

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

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

Example - Region B: MAM Composites WetDry OLR SST

WetDry Tropical SSTs 200mb Vectors

Region B: SON Composites WetDry SSTs Tropical SSTs

WetDry 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.

20S20N EQ TEJ AEJ-S AEJ-N WAJ Preferable area for large-scale, organised, deep convection Preferable area for shallow convection 1000mb 200mb Seasonal rainfall (mm) Schematic depicting a favourable jet configuration for enhanced rainfall over central Africa (note: Example shown for when the AEJ-S is present). 500mb

20S20N EQ TEJ AEJ-SAEJ-N WAJ Preferable area for large-scale, organised, deep convection Preferable area for shallow convection 1000mb 200mb Seasonal rainfall (mm) 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? 500mb ?

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

NCEP minus PRECIS model example: JJA

NCEP vs. ERA40 A comparison of reanalysis data over central Africa.

Region B MAM: ERANCEP

Region B: ERANCEP

Region B MAM: ERANCEP

Region B: ERANCEP

Region B: ERANCEP

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.