The influence of ENSO-type on rainfall characteristics over Southern Africa during the austral summer

Although the El Niño-Southern Oscillation (ENSO) is the leading mode of climate variability in southern Africa during the austral summer season, the impacts are nonlinear and not all events result in the expected impact. Limited work has been carried out to explore the role ENSO diversity plays in southern African climate, which this study aims to address. Here, the influence of El Niño diversity on rainfall characteristics and whether the impact evolves on sub-seasonal scales are examined. Two broad types of El Niño events, namely Eastern Pacific (EP) and Central Pacific (EP) events, are first determined by the location of the positive SST anomaly in the equatorial Pacific. For the 1950-2022 period, 9 EP El Niño events and 10 CP El Niño events are identified. Results show significant variability in ENSO impacts on a sub-seasonal scale across southern Africa during the summer half of the year (October-March). EP events affect rainfall throughout the summer, with the strongest impacts in the core months (Dec-Jan), characterized by less rainfall, more frequent dry spells and extended dry periods. EP events have a stronger relationship with various rainfall characteristics across most of southern Africa compared to CP events. Consequently, the likelihood of experiencing a significant summer rainfall deficit is higher during EP events. These findings indicate that traditional seasonal definitions, like JFM, or generalizing ENSO as a single type of event, may be inadequate in assessing ENSO-induced rainfall impacts from a seasonal forecasting perspective.