Validation of coupled GCM and projection of summer rainfall change over South Africa by the use of Statistical downscaling method

Abstract

In this study, the southern African climate response to increasing amounts of greenhouse gases is investigated, based on the dataset of a 150-yr climate change experiment following the IPCC Special Report on Emissions Scenarios marker scenario B2 (SRES-B2) performed with the coupled ARPEGE/OPA/GELATO general circulation model (GCM). The method of canonical correlation analysis (CCA) is adopted to validate the ability of the GCM to simulate the present-day climate over the southern African region and project the late-summer rainfall change over South Africa at the end of the 21st century. The model validation shows that the ARPEGE/OPA/GELATO GCM is able to capture the observed link between rainfall over South Africa and adjacent sea-level pressure (SLP), despite the existence of some systematic errors. The structure and variability of SLP are reproduced by the GCM in a realistic way. The major controlling mechanism of rainfall over South Africa can be identified in the GCM. The projection of rainfall indicates a drying trend during the 21st century over most parts of South Africa, in particular the central interior. Compared to present-day climatology, the overall late-summer rainfall will decrease by 8.2% by the end of 21st century as derived from GCM grid-point output, and by 16.1% from the downscaling model.