High resolution model projections of tropical cyclone landfall over southern Africa under enhanced anthropogenic forcing

Abstract

Tropical cyclone landfall within the southwest Indian Ocean (SWIO) basin occurs on average about 3 times per year over Mozambique and Madagascar. Rainfall associated with tropical cyclones over the interior of southern Africa can also cause widespread flooding over the eastern parts of the southern African interior, and contributes to a large extent to the widespread heavy rainfall events over that area. While a decrease has been noted in the landfall of tropical cyclones from the SWIO, no such change has been noted when all closed warm-core low pressure systems are considered. Several studies have through the use of coupled global circulation models globally reported a projected decrease in the number of tropical cyclones expected under enhanced anthropogenic forcing but an increase in the maximum wind strength obtained. In this study, a closed-low finding-and-tracking algorithm based on the identification of all 700 hPa minima and the temporal tracking of these minima subjected to various tracking criteria were performed. The ensemble of six CCAM members has yielded realistic closed warm low pressure system tracks over the SWIO and into southern Africa under current conditions. The change in track characteristics of tropical systems in the southern African region seems to be the result of a relatively large strengthening of the subtropical high pressure system over the eastern parts of southern Africa. The change is also reflected by a decrease in average January-to-March rainfall over the same region.