Examining the role of unusually warm Indo-Pacific sea surface temperatures in recent African droughts

Southern Africa (SA) and Eastern Africa (EA) experienced a sequence of severe droughts in December-January-February (SA DJF) 2015-16, October-November-December (EA OND) 2016 and March-April-May, 2017 (EA MAM). This sequence contributed to severe food insecurity. While climate variability in these regions is very complex, the goal of this study is to analyze the potential role played by unusually warm Indo-Pacific SS, where unusual is defined as a 1-in-6 year event. We use observed sea surface temperatures (SST) and satellite-gauge rainfall observations, a 20-member ensemble of Community Atmospheric Model version 5.1 simulations (CAM5), and a 40-member ensemble of climate change simulations from the Community Earth Systems Model version 1 (CESM1) Large Ensemble Community Project (LENS) to explore climate conditions associated with warm events identified based on eastern and western Pacific sea surface temperatures (SST). Our analysis suggests that strong El Ninos may be followed by warm western Pacific SST conditions, which can lead to creating conditions conducive for successive and potentially predictable droughts in SA DJF, EA OND and EA MAM. We show that different regions of warm SST appear related to recent droughts – SA DJF: Nino 3.4, EA OND: Western Equatorial Pacific (WEP), and EA MAM: Western North Pacific (WNP). For DJF and MAM, respectively, the CAM5 model driven with observed SST and the same model driven within a climate change experiment indicate that warmer El Ninos and WNP events produce more intense atmospheric responses, potentially associated with more severe droughts. OND climate seems to be strongly influenced by the Indian Ocean Dipole, which corresponds to some WEP events. We suggest the extreme SST events responsible for 2015-17 droughts are likely to reoccur, thus humanitarian agencies should consider multiyear drought and substantial food insecurity in SA and EA.