摘要：We investigate the impact of model formulation and horizontal resolution onthe ability of Regional Climate Models (RCMs) to simulate precipitation inAfrica. Two RCMs (SMHI-RCA4 and HCLIM38-ALADIN) are utilized for downscalingthe ERA-Interim reanalysis over Africa at four different resolutions: 25,50, 100, and 200 km. In addition to the two RCMs, two different parametersettings (configurations) of the same RCA4 are used. By contrastingdifferent downscaling experiments, it is found that model formulation hasthe primary control over many aspects of the precipitation climatology inAfrica. Patterns of spatial biases in seasonal mean precipitation are mostlydefined by model formulation, while the magnitude of the biases is controlledby resolution. In a similar way, the phase of the diurnal cycle inprecipitation is completely controlled by model formulation (convectionscheme), while its amplitude is a function of resolution. However, the impactof higher resolution on the time-mean climate is mixed. An improvement inone region/season (e.g. reduction in dry biases) often corresponds to adeterioration in another region/season (e.g. amplification of wet biases).At the same time, higher resolution leads to a more realistic distributionof daily precipitation. Consequently, even if the time-mean climate is notalways greatly sensitive to resolution, the realism of the simulatedprecipitation increases as resolution increases. Our results show thatimprovements in the ability of RCMs to simulate precipitation in Africacompared to their driving reanalysis in many cases are simply related tomodel formulation and not necessarily to higher resolution. Such modelformulation related improvements are strongly model dependent and can, ingeneral, not be considered as an added value of downscaling.
