Changes In Extreme High-temperature And Associated Population Exposure In Africa Under Global Warming Scenarios

Change in mean temperature,more frequent and intensified Extreme High-Temperatures(EHTs)are acceptable indicators of global warming,which pose serious socio-economic impacts.Previous studies revealed that many areas in Africa experienced an apparent warming rate in surface air temperature(SAT)in the last century.In addition,recent studies warned that EHTs are likely to intensify and frequently occur in the future due to climate change.Apart from changing climate,the population's size and distribution contribute to the total changes in the population exposed to EHTs.The less economically developed regions,such as Africa,are more vulnerable to the impacts of climate change.Interestingly,there exists a huge gap in the literature on the past and projected trends in mean temperature,EHTs and associated population exposure in Africa.Therefore,this study analyzed the recent past and projected changes in EHTs and population exposure to such hazards in Africa in a bid to avoid further catastrophic impacts and develop appropriate adaptation toolkits.The study utilized various ground observations,reanalysis and global climate models from the Coupled Model Intercomparison Project Phase six(CMIP6)and NCAR Community Earth System Model(CESM)Low warming simulations.Firstly,the contribution of natural and anthropogenic forcings to the observed SATvariability and change is examined from the historical CMIP6 simulations and future projections under three Shared Socioeconomic Pathways(SSP1-2.6,SSP2-4.5 and SSP5-8.5).Results indicate that from 1970 to 2010,at the continental level,SAT has increased by?0.9±0.01^?,with Greenhouse Gases(GHG),Land-Use(LU),Anthropogenic Aerosols(AA)and Natural forcing contributed by approximately 0.57±0.01^?,0.28±0.003^?,0.07±0.004^? and-0.003±0.001^?,respectively.Overall,it is found that GHG and LU change are the leading contributors to the observed warming in historical SAT over most African regions,while AA shows a cooling effect.Under both SSP1-2.6 and SSP2-4.5 emission scenarios,the SAT increases to 2059 and declines afterwards.On the other hand,under SSP5-8.5,the SAT is projected to increase throughout the 21^st century.Nevertheless,proper management of Land use and control of anthropogenic factors may lead to a substantial reduction in further warming over Africa.Secondly,due to the lack of extensive research assessing historical characteristics of EHTs in Africa,in the present research,the Climate Prediction Center daily minimum and maximum temperature are used to characterize historical EHTs into the intensity of hot days(TXx),hot nights(TNx),and frequency indices based on the 90^th percentile of hot days(TX90p)and hot nights(TN90p)as defined by the Expert Team on Climate Change Detection Indices(ETCCDI)from 1981 to 2020 over Africa.Results show that many parts of Africa experienced more frequent and intensified hot days and nights in the current period(1998-2020)compared to the recent past(1981-1997),suggesting a clear shift in climate.Thus,we used the climatological mean differences between meteorological parameters before and after the breakpoint to assess the relationship between atmospheric conditions and EHTs.As a result,we found that the current period observed an increase in the geopotential height at 500 h Pa and reduced total cloud cover,as well as an increase in upward longwave radiation resulting in an upsurge in the frequency of hot days over many African Sub-regions.Furthermore,the ensemble mean of global climate models from the CMIP6 and population projection was used to assess the future changes in EHTs and exposure to the population by the middle of this century(2041-2060)in Africa compared to the recent climate taken from 1991 to 2010.The intensity of EHT is anticipated to escalate between 0.25 to 1.8^? and 0.6 to 4^? under SSP2-4.5 and SSP5-8.5,respectively,with Sahara(SAH)and West Southern Africa(WSAF)projected to warm faster than the rest of the regions.On average,warm days'frequency is also expected to upsurge under SSP2-4.5(26-59%)and SSP5-8.5(30-69%)relative to the recent climate.By the mid-21^st century,continental population exposure is expected to upsurge by?25%(28%)of the reference period under SSP2-4.5(SSP5-8.5).The highest increase in exposure is expected in most parts of West Africa(WAF),followed by East Africa.The projected changes in continental exposure(?353.6 million person-days under SSP2-4.5 and?401.4 million person-days under SSP5-8.5)are mainly due to the interaction effect.However,the climate's influence is more than the population,especially for WAF,South-East Africa(SEAF)and East Southern Africa(ESAF).Following the December 2015 Paris Agreement,there is an international effort to limit global warming at 1.5^? and 2.0^? relative to the pre-industrial level.However,there is inadequate research quantifying the difference in extreme temperature between the two target levels,especially in Africa.This dissertation used historical and future low-warming projections of NCAR-CESM to assess the differences in extreme temperature events under 1.5^? and 2.0^? future scenarios relative to the recent climate taken from 1976-2005 over Africa.The results show that compared with the present day,the magnitude of the highest temperature(TXx)will increase by approximately 1.6^?/2.2^? in 1.5^?/2.0^? warming worlds,with more substantial warming in SAH and Southern Africa(SAF)regions.The frequency of hot days(TX90p)is projected to increase with global warming across the continent,with a high increase in SAF and SAH.Assessment of the avoided impacts in 1.5^? relative to 2.0^? indicates that limiting global warming at 1.5^? rather than 2.0^? could reduce the intensity,frequency,and duration of extreme temperatures from 12-55%.However,the magnitude of avoided impacts differs among indices and sub-regions.Hence,limiting warming to 1.5^? instead of 2.0^? could result in significant benefits for Africa.