The impact of regional climate model formulation and resolution on simulated precipitation in Africa
2020
Abstract. We investigate the impact of model formulation and horizontal resolution on
the ability of Regional Climate Models (RCMs) to simulate precipitation in
Africa. Two RCMs (SMHI-RCA4 and HCLIM38-ALADIN) are utilized for downscaling
the ERA-Interim reanalysis over Africa at four different resolutions: 25,
50, 100, and 200 km. In addition to the two RCMs, two different parameter
settings (configurations) of the same RCA4 are used. By contrasting
different downscaling experiments, it is found that model formulation has
the primary control over many aspects of the precipitation climatology in
Africa. Patterns of spatial biases in seasonal mean precipitation are mostly
defined by model formulation, while the magnitude of the biases is controlled
by resolution. In a similar way, the phase of the diurnal cycle in
precipitation is completely controlled by model formulation (convection
scheme), while its amplitude is a function of resolution. However, the impact
of higher resolution on the time-mean climate is mixed. An improvement in
one region/season (e.g. reduction in dry biases) often corresponds to a
deterioration in another region/season (e.g. amplification of wet biases).
At the same time, higher resolution leads to a more realistic distribution
of daily precipitation. Consequently, even if the time-mean climate is not
always greatly sensitive to resolution, the realism of the simulated
precipitation increases as resolution increases. Our results show that
improvements in the ability of RCMs to simulate precipitation in Africa
compared to their driving reanalysis in many cases are simply related to
model formulation and not necessarily to higher resolution. Such model
formulation related improvements are strongly model dependent and can, in
general, not be considered as an added value of downscaling.
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