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Simulation of the annual and diurnal cycles of rainfall over South Africa by a regional climate model |
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| Authors: | Benjamin Pohl Mathieu Rouault Shouraseni Sen Roy |
| Institution: | 1. Centre de Recherches de Climatologie, UMR6282 Biogéosciences, CNRS/University of Burgundy, 6 Boulevard Gabriel, 21000, Dijon, France 2. Department of Oceanography, Mare Institute, University of Cape Town, Cape Town, South Africa 3. Nansen-Tutu Center for Marine Environmental Research, University of Cape Town, Cape Town, South Africa 4. Department of Geography and Regional Studies, University of Miami, Coral Gables, FL, 33124, USA |
| Abstract: | The capability of a current state-of-the-art regional climate model for simulating the diurnal and annual cycles of rainfall over a complex subtropical region is documented here. Hourly rainfall is simulated over Southern Africa for 1998–2006 by the non-hydrostatic model weather research and forecasting (WRF), and compared to a network of 103 stations covering South Africa. We used five simulations, four of which consist of different parameterizations for atmospheric convection at a 0.5 × 0.5° resolution, performed to test the physic-dependency of the results. The fifth experiment uses explicit convection over tropical South Africa at a 1/30° resolution. WRF simulates realistic mean rainfall fields, albeit wet biases over tropical Africa. The model mean biases are strongly modulated by the convective scheme used for the simulations. The annual cycle of rainfall is well simulated over South Africa, mostly influenced by tropical summer rainfall except in the Western Cape region experiencing winter rainfall. The diurnal cycle shows a timing bias, with atmospheric convection occurring too early in the afternoon, and causing too abundant rainfall. This result, particularly true in summer over the northeastern part of the country, is weakly physic-dependent. Cloud-resolving simulations do not clearly reduce the diurnal cycle biases. In the end, the rainfall overestimations appear to be mostly imputable to the afternoon hours of the austral summer rainy season, i.e., the periods during which convective activity is intense over the region. |
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