Editing IPCC:AR6/WGII/Chapter-9 (section)

==== 9.5.5.2 Precipitation ====

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===== 9.5.5.2.1 Observations =====

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Over equatorial east Africa the short rains (October–November–December) have shown a long-term wetting trend from the 1960s until present ( [[#Manatsa--2013|Manatsa and Behera, 2013]] ; [[#Nicholson--2015|Nicholson, 2015]] ; 2017), which is linked with western Indian Ocean warming and a steady intensification of Indian Ocean Walker Cell ( [[#Liebmann--2014|Liebmann et al., 2014]] ; [[#Nicholson--2015|Nicholson, 2015]] ).

In contrast, the long rainfall season (March–April–May) has experienced a long-term drying trend between 1986 and 2007, with rainfall declines in each of these months and a shortening of the wet season ( [[#Rowell--2015|Rowell et al., 2015]] ; [[#Wainwright--2019|Wainwright et al., 2019]] ). Unlike previous decades, since around 2000, the long rains have exhibited a significant relationship with the El Niño-Southern Oscillation (ENSO) ( [[#Park--2020|Park et al., 2020]] ), as multiple droughts have occurred during recent La Niña events and when the western to central Pacific sea surface temperature gradient was La Niña-like ( [[#Funk--2015|Funk et al., 2015]] ; [[#Funk--2018a|Funk et al., 2018a]] ). Wetter-than-average rainfall years within this long-term drying trend are often associated with a stronger amplitude of the Madden–Julian Oscillation ( [[#Vellinga--2018|Vellinga and Milton, 2018]] ).

In the northern, summer rainfall region (June–September), a decline in rainfall occurred in the 1960s and rainfall has remained relatively low, while interannual variability has increased since the late 1980s ( [[#Nicholson--2017|Nicholson, 2017]] ); the cause of this drying trend is uncertain.

Since 2005, drought frequency has doubled from once every 6 to once every 3 years and has become more severe during the long and summer rainfall seasons than during the short rainfall season ( [[#Ayana--2016|Ayana et al., 2016]] ; [[#Gebremeskel%20Haile--2019|Gebremeskel Haile et al., 2019]] ). Several prolonged droughts have occurred predominantly within the arid and semi-arid parts of the region over the past three decades ( [[#Nicholson--2017|Nicholson, 2017]] ).

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===== 9.5.5.2.2 Projections =====

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Higher mean annual rainfall, particularly in the eastern parts of east Africa are projected at GWL 1.5°C and 2°C by 25 CORDEX models ( [[#Nikulin--2018|Nikulin et al., 2018]] ; [[#Osima--2018|Osima et al., 2018]] ). The additional 0.5°C of warming from 1.5°C increases average dry spell duration by between two and four days, except over southern Somalia where this is reduced by between 2–3 days ( [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Nikulin--2018|Nikulin et al., 2018]] ; [[#Osima--2018|Osima et al., 2018]] ; [[#Weber--2018|Weber et al., 2018]] ).

During the short rainy season, a longer rainfall season ( [[#Gudoshava--2020|Gudoshava et al., 2020]] ) and increased rainfall of over 100 mm on average is projected over the eastern Horn of Africa and regions of high/complex topography at GWL 4.5°C ( [[#Dunning--2018|Dunning et al., 2018]] ; [[#Endris--2019|Endris et al., 2019]] ; [[#Ogega--2020|Ogega et al., 2020]] ).

During the long rainy season, there is ''low confidence'' in projected mean rainfall change ( [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ). Although some studies report projected increased end of century rainfall ( [[#Otieno--2013|Otieno and Anyah, 2013]] ; [[#Kent--2015|Kent et al., 2015]] ), the mechanisms responsible for this are not well-understood and a recent regional model study has detected no significant change ( [[#Cook--2020b|Cook et al., 2020b]] ). Projected wetting is opposite to the observed drying trends, giving rise to the ‘east African rainfall paradox’ ( [[#Rowell--2015|Rowell et al., 2015]] ; [[#Wainwright--2019|Wainwright et al., 2019]] ). In other parts of east Africa, no significant trend is evident ( [[#Ogega--2020|Ogega et al., 2020]] ), agreement on the sign of change is low, and in some regions, CMIP5 and CORDEX data show opposite signs of change ( [[#Lyon--2017|Lyon et al., 2017]] ; [[#Lyon--2017|Lyon and Vigaud, 2017]] ; [[#Osima--2018|Osima et al., 2018]] ; [[#Kendon--2019|Kendon et al., 2019]] ; [[#Ogega--2020|Ogega et al., 2020]] ).

Heavy rainfall events are projected to increase over the region at global warming of 2°C and higher ( ''high confidence'' ) ( [[#Nikulin--2018|Nikulin et al., 2018]] ; [[#Finney--2020|Finney et al., 2020]] ; [[#Ogega--2020|Ogega et al., 2020]] ; [[#Li--2021|Li et al., 2021]] ). Drought frequency, duration and intensity are projected to increase in Sudan, South Sudan, Somalia and Tanzania but decrease or not change over Kenya, Uganda and the Ethiopian Highlands ( [[#Liu--2018c|Liu et al., 2018c]] ; [[#Nguvava--2019|Nguvava et al., 2019]] ; [[#Haile--2020|Haile et al., 2020]] ; [[#Spinoni--2020|Spinoni et al., 2020]] ).

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