Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.6.2.6 Future Climate Information from Global Simulations ====

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Global models show strong consistency in a drying signal for the Cape Town region, with the reduction in total annual rainfall of up to 20% by the end of the 21st century in CMIP5 RCP8.5 and CMIP6 SSP5-8.5 simulations (Figure 10.18; [[#Almazroui--2020c|Almazroui et al., 2020c]] ). The consistency across the models is a robust signal compared to the rest of southern Africa, where the climate change signal varies spatially: stronger drying in the west and moderate drying or weak wetting in the east ( [[#DEA--2013|DEA, 2013]] , 2018; see Atlas.4.4 for further discussion of southern Africa precipitation projections). Rainfall changes projected for the Cape Town region are consistent with projected changes in hemispheric-scale processes and regional-scale dynamics that point toward reduced frequency of frontal systems affecting that region. These changes include robust signals in CMIP5 models for the Southern Hemisphere for a poleward expansion of the tropics ( [[#Hu--2013b|Hu et al., 2013b]] ), poleward displacement of mid-latitude storm tracks ( [[#Chang--2012|Chang et al., 2012]] ), increased strength and poleward shift of the westerly winds ( [[#Bracegirdle--2018|Bracegirdle et al., 2018]] ) and subtropical jet-streams ( [[#Chenoli--2017|Chenoli et al., 2017]] ), and a shift toward a more positive phase of the SAM (E.-P. [[#Lim--2016|]] [[#Lim--2016|Lim et al., 2016]] ). However, despite the consistency in circulation changes, the emergence of anthropogenic rainfall change above unforced variability in West Southern Africa remains uncertain for annual rainfall throughout most of the 21st century, even under SSP5-8.5 (Figure 10.15).

There is also a substantial increase in the frequency of conditions supporting atmospheric rivers and water vapour transport towards the south-west coast of southern Africa in the projected climate ( [[#Espinoza--2018|Espinoza et al., 2018]] ). This behaviour has strong implications for the region, as most topographically high locations receive rainfall from persistent atmospheric rivers ( [[#Blamey--2018|Blamey et al., 2018]] ). A thorough understanding of the role of atmospheric rivers in the Cape Town region under a changing climate is missing.

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