Simulating the Surface Solar Irradiance of Africa Using a Regional Climate Model: Influence of Vegetation-Runoff Coupled System

Abstract

Surface solar irradiance (SSI) is influenced by important factors such as total cloud cover and aerosols. However, the influence of vegetation-runoff coupled system on SSI has not been investigated yet. The present study aims to study this issue in tropical Africa within the framework of the regional climate model (RegCM4) using two runoff schemes: (TOPMODEL; TOP and Variable Infiltration Capacity; VIC). For the vegetation-runoff systems to be coupled, the Carbon-Nitrogen (CN) module was enabled. The two simulations were designated as: CN-TOP and CN-VIC. Furthermore, the RegCM4 was downscaled by NCEP/NCAR2 reanalysis for a duration of 13 years and evaluated with respect to a reliable reanalysis product. The results showed that the CN-VIC outperforms the CN-TOP in all seasons particularly during the summer season. For instance, the CN-VIC underestimates the SSI over the Northern Savannah region by 15 W m−2; while the CN-TOP underestimates the SSI by 30–50 W·m−2. Over different sub-regions, the CN-VIC performs better than the CN-TOP over Northern Savanna during the summer season and over the Congo basin during the winter season. Moreover, the four parameters of the VIC surface dataset need to be recalibrated with respect in-situ observation of tropical Africa, and additional sensitivity experiments are needed to ensure a better performance of the CN-VIC.

Keywords

• regional climate model
• surface solar irradiance
• tropical Africa
• vegetation-runoff