Climate Dynamics

, Volume 38, Issue 3–4, pp 613–634 | Cite as

Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF

  • Julien Crétat
  • Benjamin Pohl
  • Yves Richard
  • Philippe Drobinski


This study aims at quantifying seasonal biases of regional climate model outputs during southern African summer, against a dense in situ measurement network (daily rain-gauge and surface air temperature records, and 12 h UTC radiosondes), and uncertainties associated with some physical parameterizations. Using the non-hydrostatic Advanced Research Weather Forecast (WRF) laterally forced by ERA40 reanalysis, twenty-seven experiments configured with three schemes of cumulus (CU), planetary boundary layer (PBL) and microphysics (MP), are performed at 35 km horizontal resolution during the core of a summer rainy season (December 1993 to February 1994 season) representative of the South African rainfall climatology. WRF simulates accurately seasonal large-scale rainfall patterns, as well as seasonal gradients of South African rainfall and 2-m temperature, and seasonal vertical profiles of the air temperature and humidity. However seasonal biases fluctuate strongly from an experiment to another, denoting considerable uncertainties generated by the physical package. Rainfall amounts are the most sensitive parameter to the tested schemes. Their geography, intensity, and intraseasonal characteristics are predominantly sensitive to CU schemes, and much less to PBL and MP schemes. Some CU-PBL combinations produce additive effects, which can dramatically either reduce or increase biases. Satisfactory configurations are found for South African climate, which would not have been possible without testing numerous physical parameterizations.


Physical parameterization Southern Africa Summer rainfall WRF regional climate model 



Rainfall and 2-m air temperature was provided by the South African Water Research Commission. Radiosondes are available freely from the Wyoming University web site ( ECMWF ERA-40 data was provided by the ECMWF Meteorological Archival and Retrieval System (MARS) Data Server. WRF was provided by the University Corporation for Atmospheric Research ( The authors are grateful to Sivarajan Sijikumar, Thierry Castel, Pascal Roucou and Nicolas Vigaud for helpful discussions on WRF. Calculations were performed using HPC resources from DSI-CCUB (Université de Bourgogne).


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© Springer-Verlag 2011

Authors and Affiliations

  • Julien Crétat
    • 1
  • Benjamin Pohl
    • 1
  • Yves Richard
    • 1
  • Philippe Drobinski
    • 2
  1. 1.Centre de Recherches de Climatologie, CNRS UMR 5210, Université de BourgogneDijonFrance
  2. 2.LMDInstitut Pierre Simon Laplace, Ecole PolytechniquePalaiseauFrance

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