Sensitivity of West African Monsoon water cycle to land surface schemes in RegCM4

Abstract:

The West African rainfall regime constitutes a considerable challenge for Regional Climate Modeling due to the complexity of dynamical and physical processes, that characterise the West African Monsoon (WAM) system. In this paper sensitivity experiments are carried out to investigate the effects of different RegCM4 land-surface schemes on atmospheric water (Precipitation minus Evaporation, P-E) and moisture fluxes over the WAM region over the period 1998-2009. Two groups of thirteen years’ (1997-2009) numerical experiments were performed based on two land-surface scheme : Biosphere-Atmosphere Transfer Sscheme (BATS) and Community Land Model version 4.5 (CLM45). The two experiments share the same domain, initial and lateral boundary conditions, cumulus convective scheme and spatial resolution. Results show that, use of CLM instead of BATS results in a drier land surface and a better simulation of the seasonal average spatial pattern and seasonal cycle of precipitation as well as atmospheric water budget components. However, both experiments are in agreement that, West Africa is alternatively a net source and sink region of atmospheric moisture, depending on the season (a sink during the wet season and a source during the dry season). A strong correlations are found between moisture flux convergence and precipitation over WAM regions, while the relation between evaporation and precipitation is very differen tbetween Sahel and Guinean region.The West African rainfall regime constitutes a considerable challenge for Regional Climate Modeling due to the complexity of dynamical and physical processes, that characterise the West African Monsoon (WAM) system. In this paper sensitivity experiments are carried out to investigate the effects of different RegCM4 land-surface schemes on atmospheric water (Precipitation minus Evaporation, P-E) and moisture fluxes over the WAM region over the period 1998-2009. Two groups of thirteen years’ (1997-2009) numerical experiments were performed based on two land-surface scheme : Biosphere-Atmosphere Transfer Sscheme (BATS) and Community Land Model version 4.5 (CLM45). The two experiments share the same domain, initial and lateral boundary conditions, cumulus convective scheme and spatial resolution. Results show that, use of CLM instead of BATS results in a drier land surface and a better simulation of the seasonal average spatial pattern and seasonal cycle of precipitation as well as atmospheric water budget components. However, both experiments are in agreement that, West Africa is alternatively a net source and sink region of atmospheric moisture, depending on the season (a sink during the wet season and a source during the dry season). A strong correlations are found between moisture flux convergence and precipitation over WAM regions, while the relation between evaporation and precipitation is very differen tbetween Sahel and Guinean region.