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

=== Atlas.4.4 Assessment and Synthesis of Projections ===

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Research over Africa has improved since AR5, and although SR1.5 ( [[#de%20Coninck--2018|de Coninck et al., 2018]] ) has synthesized new information for the continent, there is still not enough literature on specific areas for assessment. CMIP5 and CMIP6 projections (Figure Atlas.1 6) are for continued warming, with median projected regional warming for 2080–2100 compared to 1995–2014 of between 1°C and 2°C under SSP1-2.6/RCP2.6 emissions and exceeding 4°C and in some regions 5°C under SSP5-8.5/RCP8.5 emissions. The central interiors of southern and northern Africa are ''likely'' to warm faster than equatorial and tropical regions (Interactive Atlas). Projections from CMIP5 show that East Africa is ''likely'' to warm by 1.7°C–2.8°C and 2.2°C–5.4°C under the RCP4.5 and RCP8.5 scenarios respectively in the period 2071–2100 relative to 1961–1990 ( [[#Ongoma--2018|Ongoma et al., 2018]] ). Over southern Africa, areas in the south-western region of the sub-continent, covering South Africa and parts of Namibia and Botswana, are projected to experience the largest increase in temperature, which are expected to be greater than the global mean warming ( [[#Maúre--2018|Maúre et al., 2018]] ). A large ensemble of CORDEX Africa simulations have been used to project the impact of 1.5°C and 2°C GWLs ( [[#Klutse--2018|Klutse et al., 2018]] ; [[#Lennard--2018|Lennard et al., 2018]] ; [[#Maúre--2018|Maúre et al., 2018]] ; [[#Mba--2018|Mba et al., 2018]] ; [[#Nikulin--2018|Nikulin et al., 2018]] ; [[#Osima--2018|Osima et al., 2018]] ). While a few studies addressed the whole African continent ( [[#Lennard--2018|Lennard et al., 2018]] ; [[#Nikulin--2018|Nikulin et al., 2018]] ), some focused on specific regions of Africa ( [[#Diedhiou--2018|Diedhiou et al., 2018]] ; [[#Klutse--2018|Klutse et al., 2018]] ; [[#Kumi--2018|Kumi and Abiodun, 2018]] ; [[#Maúre--2018|Maúre et al., 2018]] ; [[#Mba--2018|Mba et al., 2018]] ). CORDEX simulations project robust warming over Africa in excess of the global mean ( [[#Lennard--2018|Lennard et al., 2018]] ; [[#Nikulin--2018|Nikulin et al., 2018]] ), and over West Africa the magnitude of regional warming reaches the 2080–2100 global warming level one to two decades earlier ( [[#Mora--2013|Mora et al., 2013]] ; [[#Niang--2014|Niang et al., 2014]] ; [[#Sylla--2016|Sylla et al., 2016]] ; [[#Klutse--2018|Klutse et al., 2018]] ). Temperature increases projected under RCP8.5 over Sudan and northern Ethiopia imply that the Greater Horn of Africa would warm faster than the global mean relative to 1971–2000 ( [[#Osima--2018|Osima et al., 2018]] ). Over North Africa, summer mean temperatures from CORDEX, CMIP5 (RCP8.5) and CMIP6 (SSP5-8.5) are projected to increase beyond 6°C by the end of the century with respect to the period 1970–2000 ( [[#Schilling--2012|Schilling et al., 2012]] ; [[#Ozturk--2018|Ozturk et al., 2018]] ; [[#Almazroui--2020c|Almazroui et al., 2020c]] ), see also the Interactive Atlas. Note that results for the CORDEX-AFR over the Mediterranean (MED) are consistent with those reported from the CORDEX-EUR dataset (Figure Atlas.24; Section [[#Atlas.1.3|Atlas.1.3]] ), in agreement with [[#Legasa--2020|Legasa et al. (2020)]] .

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[[File:d9420961f942e86c62f8c331dfa9f080 IPCC_AR6_WGI_Atlas_Figure_16.png]]

'''Figure Atlas.16''' '''|''' '''Regional changes over land in annual mean surface air temperature and precipitation relative to the 1995–2014 baseline for the reference regions in Africa (warming since the 1850–1900 pre-industrial baseline is also provided as an offset).''' Bar plots in the left panel of each region triplet show the median (dots) and 10th–90th percentile range (bars) across each model ensemble for annual mean temperature changes for four datasets (CMIP5 in intermediate colours; a subset of CMIP5 used to drive CORDEX in light colours; CORDEX overlying the CMIP5 subset with dashed bars; and CMIP6 in solid colours); the first six groups of bars represent the regional warming over two time periods (near-term 2021–2040 and long-term 2081–2100) for three scenarios (SSP1-2.6/RCP2.6, SSP2-4.5/RCP4.5 and SSP5-8.5/RCP8.5), and the remaining bars correspond to four global warming levels (GWLs: 1.5°C, 2°C, 3°C and 4°C). The scatter diagrams of temperature against precipitation changes display the median (dots) and 10th–90th percentile ranges for the above four warming levels for December–January–February–March (DJFM; middle panel) and June–July–August–September (JJAS; right panel), respectively; for the CMIP5 subset only the percentile range of temperature is shown, and only for 3°C and 4°C GWLs. Changes are absolute for temperature (in °C) and relative (as %) for precipitation. See [[#Atlas.1.3|Atlas.1.3]] for more details on reference regions ( [[#Iturbide--2020|Iturbide et al., 2020]] ) and [[#Atlas.1.4|Atlas.1.4]] for details on model data selection and processing. The script used to generate this figure is available online ( [[#Iturbide--2021|Iturbide et al., 2021]] ) and similar results can be generated in the Interactive Atlas for flexibly defined seasonal periods. Further details on data sources and processing are available in the chapter data table (Table Atlas.SM.15).

Projected rainfall changes over Africa in the mid- and late 21st century are uncertain in many regions, highly variable spatially and with differing levels of model agreements (Figure Atlas.1 6) though with robust projections of decreases in MED and WSAF and increases in NEAF and SEAF by 2080–2100 under high emissions (Interactive Atlas). Some uncertainties are reported over parts of Africa from CORDEX projections ( [[#Dosio--2016|Dosio and Panitz, 2016]] ; [[#Endris--2016|Endris et al., 2016]] ; [[#Klutse--2018|Klutse et al., 2018]] ). For example, large uncertainties are associated with projections at 1.5°C and 2°C of global warming over Central Africa ( [[#Mba--2018|Mba et al., 2018]] ) and over the Sahel ( [[#Gbobaniyi--2014|Gbobaniyi et al., 2014]] ; [[#Sylla--2016|Sylla et al., 2016]] ). Over southern Africa, enhanced warming is projected to result in a reduction in mean rainfall across the region ( [[#Maúre--2018|Maúre et al., 2018]] ), and in particular over the Limpopo basin and smaller areas of the Zambezi basin in Zambia, and also in parts of the Western Cape in South Africa, under a global warming of 2°C. The projections of reduced precipitation in summer rainfall regions of southern Africa are associated with delayed wet season onset in spring ( [[#Dunning--2018|Dunning et al., 2018]] ) due to a northward shift and delayed breakdown of the Congo Air Boundary ( [[#Howard--2020|Howard and Washington, 2020]] ). However, projected rainfall intensity over southern Africa is ''likely'' to increase and be magnified under RCP8.5 compared with RCP4.5 for the period 2069–2098 relative to the reference period 1976–2005 ( [[#Pinto--2018|Pinto et al., 2018]] ). For West Africa, rainfall projection is uncertain because of the contrasting signals from models ( [[#Dosio--2019|Dosio et al., 2019]] ). Nonetheless, West Africa river basin-scale irrigation potential would decline under 2°C of global warming even for areas where water availability increases ( [[#Sylla--2018|Sylla et al., 2018]] ). The western and eastern Sahel are projected as hotspots for delayed rainfall onset dates of about four days and six days causing reduced length of rainy season in the 1.5°C–2°C warmer climates under RCP4.5 and RCP8.5 scenarios ( [[#Kumi--2018|Kumi and Abiodun, 2018]] ). Projected delay in rainfall cessation dates and a longer length of rainy season over the western part of the Guinea coast is ''likely'' under the same scenarios (Figure Atlas.1 6; [[#Sellami--2016|Sellami et al., 2016]] ; [[#Kumi--2018|Kumi and Abiodun, 2018]] ). There is a tendency towards an increase in annual mean precipitation over central Sahel and eastern Africa (Interactive Atlas, Figure Atlas.1 6, ( [[#Nikulin--2018|Nikulin et al., 2018]] ), especially over the Ethiopian Highlands with up to 0.5 mm day <sup>–1</sup> ( [[#Osima--2018|Osima et al., 2018]] ).

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