Later Wet Seasons with More Intense Rainfall over Africa under Future Climate Change

Abstract

Later wet seasons with more intense rainfall over Africa under future climate change Article Published Version Dunning, C., Black, E. and Allan, R. (2018) Later wet seasons with more intense rainfall over Africa under future climate change. Journal of Climate, 31. pp. 97199738. ISSN 0894 8755ABSTRACT Changes in the seasonality of precipitation over Africa have high potential for detrimental socioeconomic impacts due to high societal dependence upon seasonal rainfall. Here, for the first time we conduct a continental-scale analysis of changes in wet season characteristics under the RCP4.5 and RCP8.5 climate projection scenarios across an ensemble of CMIP5 models using an objective methodology to determine the onset and cessation of the wet season. A delay in the wet season over West Africa and the Sahel of over 5-10 days on average, and later onset of the wet season over southern Africa, is identified and associated with increasing strength of the Saharan heat low in late boreal summer and a northward shift in the position of the tropical rain belt over August-December. Over the Horn of Africa rainfall during the ''short rains'' season is projected to increase by over 100 mm on average by the end of the twenty-first century under the RCP8.5 scenario. Average rainfall per rainy day is projected to increase, while the number of rainy days in the wet season declines in regions of stable or declining rainfall (western and southern Africa) and remains constant in central Africa, where rainfall is projected to increase. Adaptation strategies should account for shorter wet seasons, increasing rainfall intensity, and decreasing rainfall frequency, which will have implications for crop yields and surface water supplies.

Projected effects of 1.5 °C and 2 °C global warming levels on the intra-seasonal rainfall characteristics over the Greater Horn of Africa

“…These results are consistent with Dunning et al (2018) who found that CMIP5 models over the equatorial region projected early-onset and cessation. Onset over equatorial East Africa is linked to the 700 mb zonal winds, the Madden Julian Oscillation, and sea surface temperature in the western Indian Ocean (Camberlin and Okoola 2003, Pohl and Camberlin 2006, Zaitchik 2017, Wainwright et al 2019.…”

“…Additional delays of up to 4 d are projected in the mean cessation date under 2°C GWL compared to 1.5°C GWL ( figure 3(h)). During this season, under the 2°C GWL, the region is projected to have a season that starts and ends later consistent with findings from Dunning et al (2018).…”

“…The extra 0.5°C warming from 1.5°C will likely prolong OND withdrawal over Uganda, Kenya and Somalia ( figure 4(h)). In a study utilising the CMIP5 models for the late 21st century, Dunning et al (2018) found similar results of late-onset and delayed cessation as with the 2°C GWL.…”

Assessment of Physical Water Scarcity in Africa Using GRACE and TRMM Satellite Data

“…For example, the peak of the Sahel droughts of 1970 to 1985, precipitation decreased by 30% [65,66], suggesting that such a magnitude of change is possible again at some point in the future. Moreover, a number of climate change projection scenarios suggest a decrease in precipitation over Northern Africa and the Western parts of Africa [67], while the Eastern and Southern Africa are highly likely to experience increase precipitation by the end of the 21st century [68,69].…”

Seasonal Forecasting of the Onset of the Rainy Season in West Africa

“…In addition, climate change seems to influence rainfall characteristics in the Sahel zone, such as false starts and early cessation of rainy seasons or increased frequency of intense daily rainfall [27,28]. Ref [29] also show an increasing precipitation intensity with a higher average precipitation per rainy day, a 5-10 days later start and end of the rainy season, but only a marginal change in the overall duration of the wet season.…”