Impact of soil moisture initialisation and lateral boundary conditions on regional climate model simulations of the West African Monsoon

In this study, we use the Met Office Hadley Centre regional climate model HadRM3P to investigate the relative impact of initial soil moisture (SM) and lateral boundary conditions (LBC) on simulations of the West African Monsoon. Soil moisture data that are in balance with our particular model are generated using a 10-year (1997-2007) simulation of HadRM3P nested within the NCEP-R2 reanalyses. Three sets of experiments are then performed for six April-October seasons (2000 and 2003-2007) to assess the sensitivity to different sources of initial SM data and lateral boundary data. The results show that the only impact of the initial SM anomalies on precipitation is to generate small random intraseasonal, interannual and spatial variations. In comparison, the influence of the LBC dominates both in terms of magnitude and spatial coherency. Nevertheless, other sources of initial SM data or other models may respond differently, so it is recommended that the robustness of this conclusion is established using other model configurations.