The influence of two land-surface hydrology schemes on the regional climate of Africa using the RegCM4 model

Two 12-year simulations were conducted with the RegCM4 model to study how different hydrology schemes can affect the terrestrial hydrology cycle, the surface energy balance, and the regional climate of Africa and in particular tropical Africa. One simulation used the default TOP hydrology scheme in the CLM4.5 land surface model; the other used the variable infiltration capacity (VIC) hydrology model coupled to CLM4.5. The results show that the VIC scheme has a lower soil infiltration rate and hence lower surface soil moisture (10 cm in this study) relative to the default TOP scheme. This leads to a different partitioning of terms in the surface energy balance, with low evapotranspiration and high sensible heat flux, resulting in a net warming effect. The VIC simulation also has low relative humidity due to the low evapotranspiration rate. The low infiltration rate of the VIC hydrology also results in accumulation of moisture on the soil surface. In addition, the VIC scheme generates more precipitation, especially in the summer (JJA) season. Thus, the hydrology parameterization can affect not just the terrestrial hydrology cycle but also energy balance partitioning and hence the surface climate. Moreover, the VIC simulation has smaller biases in the surface energy flux and other surface climate variables in comparison with the default CLM4.5 run. We conclude that the VIC land surface hydrology scheme succeeds in controlling the infiltration rate, the surface soil moisture, and hence total evapotranspiration, which improves the surface energy balance and hence produces a better surface climate. Thus, we recommend the VIC hydrology scheme for future climate studies over Africa.