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Abstract Submission No. | ABS-2022-14-0268 |
Title of Abstract | Marine heat waves and tropical cyclones - two devastating types of coastal hazard in South-eastern Africa |
Authors | daneeja mawren*, Juliet Hermes, Chris Reason |
Organisation | University of Cape Town |
Address | Private Bag X3, Rondebosch Cape Town, Western Cape, South Africa Pincode: 7700 Mobile: 608131228 E-mail: dado1307@hotmail.co.uk |
Country | South Africa |
Presentation | Oral |
Abstract | The coast of southeastern Africa is the only part of the continent to experience landfalling tropical cyclones (TCs), the most destructive and hazardous of weather systems. It is also a region which frequently experiences intense marine heat waves (MHWs). Three coastal regions in southeastern Africa with high biodiversity and relatively large populations dependent on local coral reefs and artisanal fishing are analysed in terms of their TC and MHW characteristics. Significantly increasing trends in MHW duration, frequency and intensity, TC heat potential and coral bleaching are found during austral summer in all three coastal areas, with northeastern Madagascar experiencing the fastest rate. The co-occurrence of TCs and MHWs in each region is also considered. A parameter-space plot of MHW intensity versus TC translational speed is suggested as a useful way in which to categorise and monitor such co-occurrences. Evidence is presented that pre-existing MHWs can pre-condition the ocean ahead of TC arrival which may then be favourable for storm intensification. Following TC passage, existing MHWs tend to be significantly weakened or sometimes ended by these storms as are the coral thermal stresses. Of the three coastal zones considered, northeastern Madagascar appears to be more prone to landfalling severe cyclones and hence TC-MHW co-occurrence. It is suggested that the rapid increase in surface wind friction velocity as the TC approaches the MHW region is important for the rate at which the MHW weakens towards its demise. This work highlights the complex relationship between these devastating coastal hazards with the view to raising awareness for the need for improved real time observing systems to support these vulnerable regions in both forecasting and mitigating climate change impacts. |