Joint Seminar: Updating the East African Paradox: Inconsistent Rainfall Trends between CMIP6 Models and Observations

Societies in much of the Horn of Africa are affected by variability in two distinct rainy seasons: the March-May long rains and the September-October short rains. A recent 5-season, La Niña-forced drought has renewed concerns about possible anthropogenic drying trends in the long rains, which had partially recovered after a multidecadal drying trend in the 1980s through 2000s. Despite observed drying, previous generations of global climate models (GCMs) have consistently projected long-term wetting due to increased greenhouse gas concentrations, an East African "Paradox" which complicates the interpretation of future East African rainfall projections. We investigate the Paradox in new CMIP6 and seasonal forecast models, leveraging an improved observational record and Large Ensembles to better differentiate internal and forced trends. We find that the apparent Paradox continues in CMIP6 models, is largely removed by prescribing sea surface temperatures (SSTs), and is likely caused by GCM difficulties in simulating observed tropical Pacific SST trends in recent decades. We also find, by analyzing single-forcing runs, that the Paradox is primarily found in models with both strong greenhouse gas and aerosol responses in the region. In line with arguments that these SST trends are at least partially forced anthropogenically, we recommend users of future rainfall projections in East Africa consider the possibility of long-term MAM drying despite GCM wetting, and call for future model simulations that better sample the expected spread of SSTs. I will conclude by placing these results in the broader context of the impact of climate uncertainty on projections of the impacts of climate change on society.




13:30–14:45 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Hernan Campos

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