The Role of Moisture Schemes in Regional Climate Modeling of Precipitation over the Horn of Africa

This study aims to evaluate the performance of the latest Regional Climate Model version 4 (RegCM4) to simulate the precipitation over the Horn of Africa. Although there are several aspects in which the model can be improved, the focus of this study is to tackle the problem of its moisture scheme. RegCM4 moisture scheme has fourteen moisture scheme parameters, which can be tuned within the allowed physical limits. Each of the fourteen moisture parameters have been varied around the current default setting and over 80 model runs have been performed for a domain defined by 60km resolution, 18 vertical levels covering spatially the whole Africa and the major circulation patterns that derive climate over the region. We have found physical sound set of moisture scheme parameters to be used in the fourteen moisture scheme parameters that have significantly reduced bias in RegCM4 precipitation; improved correlation of RegCM4 precipitation with respect GPCP and CMAP; and captured seasonal and interannual variations over most of the 12 delineated homogeneous regions of Horn of Africa.