Abstract
We provide an assessment of future daily characteristics of African precipitation by explicitly comparing the results of large ensembles of global (CMIP5, CMIP6) and regional (CORDEX, CORE) climate models, specifically highlighting the similarities and inconsistencies between them. Results for seasonal mean precipitation are not always consistent amongst ensembles: in particular, global models tend to project a wetter future compared to regional models, especially over the Eastern Sahel, Central and East Africa. However, results for other precipitation characteristics are more consistent. In general, all ensembles project an increase in maximum precipitation intensity during the wet season over all regions and emission scenarios (except the West Sahel for CORE) and a decrease in precipitation frequency (under the Representative Concentration Pathways RCP8.5) especially over the West Sahel, the Atlas region, southern central Africa, East Africa and southern Africa. Depending on the season, the length of dry spells is projected to increase consistently by all ensembles and for most (if not all) models over southern Africa, the Ethiopian highlands and the Atlas region. Discrepancies exist between global and regional models on the projected change in precipitation characteristics over specific regions and seasons. For instance, over the Eastern Sahel in July–August most global models show an increase in precipitation frequency but regional models project a robust decrease. Global and regional models also project an opposite sign in the change of the length of dry spells. CORE results show a marked drying over the regions affected by the West Africa monsoon throughout the year, accompanied by a decrease in mean precipitation intensity between May and July that is not present in the other ensembles. This enhanced drying may be related to specific physical mechanisms that are better resolved by the higher resolution models and highlights the importance of a process-based evaluation of the mechanisms controlling precipitation over the region.
Highlights
In the recent decades, Africa has been affected by significant precipitation variability, including severe droughts in the Horn of Africa and West Africa during 1970s and 1980s, a multi-year drought in South Africa’s winter rainfall region, and severe floods in countries with arid climate such as Algeria, Tunisia, Egypt and Somalia (Niang et al 2014; Burls et al 2019)
Several studies showed the ability of the Regional Climate Models (RCMs) to better simulate, compared to the driving Global Climate Models (GCMs), higher order statistics and extreme events (e.g., Giorgi et al 2014; Gibba et al 2019), first order statistics are not always improved by the downscaling (e.g., Dosio et al 2015, 2019; Akinsanola and Zhou 2019) as the geographical distribution of seasonal precipitation simulated by the RCMs is strongly affected by the boundary conditions
When model simulations are compared to a large ensemble of observational products including gauge-based, satellite-based and reanalysis products, all ensembles generally reproduce the annual cycle of monthly averaged daily precipitation over many African subregions
Summary
Africa has been affected by significant precipitation variability, including severe droughts in the Horn of Africa and West Africa during 1970s and 1980s, a multi-year drought in South Africa’s winter rainfall region, and severe floods in countries with arid climate such as Algeria, Tunisia, Egypt and Somalia (Niang et al 2014; Burls et al 2019). Future increases in radiative forcing may further increase the variability of precipitation, and lead to permanent shifts in the regional climate characteristics. Such climatic changes can be potentially detrimental to already vulnerable natural and human systems across Africa. Amongst the many works based on CMIP5 results (see Niang et al 2014), Diffenbaugh and Giorgi (2012) identified areas of the Sahel, tropical West Africa and southern Africa as hotspots of regional climate change, while several studies including e.g., Monerie et al (2017), Ongoma et al (2018), Diedhiou et al (2018) and Giannini et al (2018) analyzed multiple aspects of future precipitation characteristics over subregions across Africa
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