Editing IPCC:AR6/WGI/Chapter-12 (section)

==== 12.4.1.2 Wet and Dry ====

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'''Mean precipitation:''' Since the mid-20th century, precipitation trends have varied in Africa but notable drying trends are found in eastern, central and north-eastern parts of Southern Africa, Central Africa and in the Horn of Africa (Atlas.4.2).

There is ''high confidence'' in projected mean precipitation decreases in North Africa and West Southern Africa and ''medium confidence'' in East Southern Africa by the end of the 21st century ( [[#Dosio--2019|Dosio et al., 2019]] ; [[#Gebrechorkos--2019|Gebrechorkos et al., 2019]] ; [[#Teichmann--2021|Teichmann et al., 2021]] ; Atlas.4.5). The Western Africa region features a gradient in which precipitation decreases in the west and increases in the east and increase is also projected over Eastern Africa ( ''medium confidence'' ) (Atlas.4.5), with trends in Western Africa affecting the boreal summer monsoon ( [[#Chen--2020|Chen et al., 2020]] ). Increasing precipitation for 1.5°C and 2°C GWLs are found in central and eastern Sahel with ''low confidence'' and the wet signal is getting stronger and more extended for a 3°C and 4°C warmer world (Atlas.4.4).

A change in monsoon seasonality is also reported in Western Africa and Sahel ( ''low confidence'' ) with a forward shift in time (later onset and end; [[IPCC:Wg1:Chapter:Chapter-8#8.2|Section 8.2]] ; [[#Mariotti--2011|Mariotti et al., 2011]] ; [[#Seth--2013|Seth et al., 2013]] ; [[#Ashfaq--2021|Ashfaq et al., 2021]] ). This shift has been associated with a precipitation decrease during the monsoon season attributed to a decrease of African easterly wave activity in the 6–9-day regime ( [[#Mariotti--2014|Mariotti et al., 2014]] ) and a soil precipitation feedback reported in [[#Mariotti--2011|Mariotti et al. (2011)]] .

'''River flood:''' Generally in Africa from 1990 through 2014, annual flood frequencies have fluctuated and there is ''medium confidence'' in an upward trend in flood events occurrences (C.-J. [[#Li--2016|]] [[#Li--2016|]] [[#Li--2016|Li et al., 2016]] ). In particular, over Western Africa, upward trends in hydrological extremes such as maximum peak discharge have ''likely'' occurred during the last few decades (i.e., after 1980) and have caused increased flood events in riparian countries of rivers such as Niger, Senegal and Volta ( ''high confidence'' ) ( [[#Nka--2015|Nka et al., 2015]] ; [[#Aich--2016a|Aich et al., 2016a]] ; [[#Wilcox--2018|Wilcox et al., 2018]] ; [[#Tramblay--2020|Tramblay et al., 2020]] ). In Southern Africa, trends in flood occurrences were decreasing prior to 1980 and increasing afterwards ( ''medium confidence'' ) ( [[#Tramblay--2020|Tramblay et al., 2020]] ).

Under future climate scenarios, the extreme river discharge as characterized by the 30-year return period of 5-day average peak flow is projected to increase by the end of the century for RCP8.5 (more than 10% relative to the 1971–2000 period) for most of the tropical African river basins ( [[#Dankers--2014|Dankers et al., 2014]] ) and a consistent increase of flood magnitude is projected across humid tropical Africa by 2050 for the A1B scenario ( ''medium confidence'' ) (Figure 12.5; [[#Arnell--2013|Arnell and Gosling, 2013]] ). Specifically, in Western Africa there is not a univocal pattern of change for future projections ( [[#Roudier--2014|Roudier et al., 2014]] ); However, under RCP8.5, there is ''medium confidence'' of a projected increase of 20-year flood magnitudes by 2050 in countries within the Niger River basin ( [[#Aich--2016b|Aich et al., 2016b]] ) and ''low confidence'' ( ''limited evidence'' ) of an increase in extreme peak flows and their duration in countries of the Volta River basin by 2050 and 2090 ( [[#Jin--2018|Jin et al., 2018]] ). A significant median change of flood magnitude for the Gambia River (–4.5%) and for the Sessandra (+14.4%) and Niger (+6.1%) are projected under several scenarios between mid- and end-of-century ( [[#Roudier--2014|Roudier et al., 2014]] ). In East Africa, extreme flows are projected to increase for regions within the Blue Nile basin with ''low confidence'' ( ''limited evidence'' ) ( [[#Aich--2014|Aich et al., 2014]] ). However, uncertainty due to the climate scenario dominates the projection of extreme flows ( [[#Aich--2014|Aich et al., 2014]] ; [[#Krysanova--2017|Krysanova et al., 2017]] ) for the Blue Nile and Niger River basins. Averaged over the African continent for different levels of global warming, the present-day 100-year return period flood levels will have a return period of 40 years in 1.5°C and 2°C ( [[#Alfieri--2017|Alfieri et al., 2017]] ) and 21 years for 4°C warmer climate ( [[#Hirabayashi--2013|Hirabayashi et al., 2013]] ; [[#Alfieri--2017|Alfieri et al., 2017]] ).

'''Heavy precipitation and pluvial flood:''' [[IPCC:Wg1:Chapter:Chapter-11|Chapter 11]] found that heavy precipitation intensity and frequency has ''likely'' increased over West and East Southern Africa but there is no evidence due to a lack of studies that any significant trend is observed in any other region. In addition, East Africa has experienced strong precipitation variability and intense wet spells leading to widespread pluvial flooding events hitting most countries including Ethiopia, Somalia, Kenya and Tanzania ( ''medium confidence'' ). Finally, with respect to Southern Africa, heavy precipitations events have increased in frequency ( ''medium confidence'' ).

In West Africa and Central Africa, there is ''high confidence'' that the intensity of extreme precipitation will increase in a future climate under both RCP4.5 and RCP8.5 scenarios and 1.5°C and 2°C GWLs threatening widespread flood occurrences before, during and after the mature monsoon season (Chapter 11). Extreme precipitation intensity is also increasing in several other regions, such as SAH, NEAF, SEAF, ESAF and MDG ( ''high confidence'' ) for 2°C GWL and higher (Chapter 11).

'''Landslides:''' There is an increase in reported landslides in WAF, CAF, NEAF and SEAF in the past decades but with ''limited evidence'' of significant trends ( [[#Gariano--2016|Gariano and Guzzetti, 2016]] ; [[#Haque--2019|Haque et al., 2019]] ). There is ''low confidence'' ( ''limited evidence'' ) of a future increase in landslides in central-eastern Africa, and literature is largely missing to assess this important hazard ( [[#Gariano--2016|Gariano and Guzzetti, 2016]] ).

'''Aridity:''' Section 11.9 assesses ''medium confidence'' in observed long-term declines of soil moisture and aridity indices in several African regions (NAF, WAF). Trends in East Africa are not definitive given uncertain balances between precipitation and potential evaporation ( [[#Kew--2021|Kew et al., 2021]] ). Projected declines in precipitation and soil moisture trends indicate ''high confidence'' in increased aridity over the 21st century in NAF, WSAF and ESAF but ''low confidence'' elsewhere in Africa ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ; see also Figure 12.4j–l; [[#Gizaw--2017|Gizaw and Gan, 2017]] ). A growing number of studies provide further regional context on expanding aridity in several places in East and West Africa, respectively ( [[#Sylla--2016a|Sylla et al., 2016a]] ; [[#Liu--2018b|Liu et al., 2018b]] ; [[#Haile--2020|Haile et al., 2020]] ).

'''Hydrological drought:''' Section 11.9 noted observed decreases in hydrological drought over the Mediterranean ( ''high confidence'' ) and diminished summer river flows in West Africa ( ''medium confidence'' ). Recent regional modelling studies project substantial increases in hydrological drought affecting major West African river basins under 1.5°C and 2°C GWLs and RCP4.5 and RCP8.5 scenarios (Oguntunde et al. 2018, 2020; [[#Sylla--2018b|Sylla et al., 2018b]] ); however, there remains ''low confidence'' in future projections given disagreement with global model runoff projections (e.g., B.I. [[#Cook--2020|]] [[#Cook--2020|Cook et al., 2020]] ). There is ''high confidence'' that a 2°C GWL would see an increase in hydrological droughts in the Mediterranean region, and ''medium confidence'' in increasing hydrological drought conditions in the Southern Africa regions ( [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] ).

'''Agricultural and ecological drought:''' Farmers and food security experts in East Africa have noted spatial extensions in seasonal agricultural droughts in recent decades ( [[#Elagib--2014|Elagib, 2014]] ), but it is difficult to disentangle these trends from climate variability. In Ethiopia, past severe agricultural drought conditions in the northern regions are moderately common events in recent years ( [[#Zeleke--2017|Zeleke et al., 2017]] ). In Southern Africa, the number of ‘flash’ droughts (with rapid onset and durations from a few days to couple of months) have increased by 220% between 1961 and 2016 as a result of anthropogenic warming ( [[#Yuan--2018|Yuan et al., 2018]] ). [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] notes ''medium confidence'' increases in agricultural and ecological drought trends in North, Western and Central Africa as well as both Southern Africa regions. The most striking drought is the Western Cape drought in 2015–2018, a prolonged drought that resulted in acute water shortages ( [[#Wolski--2018|Wolski, 2018]] ; [[#Burls--2019|Burls et al., 2019]] ; [[IPCC:Wg1:Chapter:Chapter-10#10.6.2|Section 10.6.2]] ). Anthropogenic climate change caused a threefold increase in the probability of such a drought to occur (Chapters 10 and 11; [[#Botai--2017|Botai et al., 2017]] ; [[#Otto--2018|Otto et al., 2018]] ). [[IPCC:Wg1:Chapter:Chapter-11#11.9|Section 11.9]] assesses increases in agricultural and ecological drought at 2°C GWL for North Africa and West Southern Africa ( ''high confidence'' ) and for East Southern Africa and Madagascar ( ''medium confidence'' ), with confidence generally rising for higher emissions scenarios ( [[#Sylla--2016b|Sylla et al., 2016b]] ; [[#Zhao--2017|Zhao and Dai, 2017]] ; [[#Diedhiou--2018|Diedhiou et al., 2018]] ; [[#Abiodun--2019|Abiodun et al., 2019]] ; [[#Todzo--2020|Todzo et al., 2020]] ; [[#Coppola--2021b|Coppola et al., 2021b]] ). [[#Liu--2018b|Liu et al. (2018b)]] identified the Southern Africa region as the drought ‘hottest spot’ in Africa in 1.5°C and 2°C global warming scenarios.

'''Fire weather:''' There is ''low confidence'' ( ''low agreement'' ) in recent reductions in fire activity given soil moisture increases in some regions and substantial land use changes ( [[#Andela--2017|Andela et al., 2017]] ; [[#Forkel--2019|Forkel et al., 2019]] ; [[#Zubkova--2019|Zubkova et al., 2019]] ). Days prone to fire conditions are going to increase in all extratropical Africa until the end of the century and fire weather indices are projected to largely increase in North and Southern Africa, where increasing aridity trends occur ( ''high confidence'' ), with an emerging signal well before the middle of the century where drought and heat increase will combine (Chapter 11; [[#Engelbrecht--2015|Engelbrecht et al., 2015]] ; [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ). There is ''low confidence'' ( ''limited evidence'' ) of fire weather changes for other African regions.

'''Total precipitation is projected to decrease in the northernmost''' ( high confidence ''') and southernmost regions of Africa''' ( medium confidence '''), with West and East Africa regions each having a west-to-east pattern of decreasing-to-increasing precipitation''' ( medium confidence '''). Most African regions will undergo an increase in heavy precipitation that can lead to pluvial floods''' ( high confidence '''), even as increasing dry climatic impact-drivers (aridity, hydrological, agricultural and ecological droughts, fire weather) are generally projected in the North Africa and Southern African regions''' ( high confidence ''') and western portions of West Africa''' ( medium confidence ''').'''

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