Assessing the influence of the El Niño–Southern Oscillation phase on rainfall variability in the Gauteng province of South Africa

Abstract

South Africa is subject to large rainfall variability, with El Niño–Southern Oscillation (ENSO) being the most important driver across the summer rainfall region. The aim of this study was to relate ENSO phase to historical rainfall variability over the densely populated and economically important Gauteng province of South Africa. Monthly rainfall totals for the period 1960–2021 were used to calculate Standardised Precipitation Index (SPI) values at different timescales for five stations. The Oceanic Niño Index (ONI) was used to classify seasons according to ENSO phase. For each station, the number of wet, near-normal or dry seasons falling in a particular ENSO phase was tallied and used to calculate probabilities of occurrence. Results revealed spatial inhomogeneities despite the study area being relatively small. Analysis of 3- and 6-month periods revealed that dry conditions occur more frequently during spring and autumn El Niño events, but are very unlikely during summer and autumn La Niña events. Analysis of 12-month periods revealed that near-normal conditions occur most frequently regardless of ENSO phase, with an increased chance of experiencing wet as opposed to dry conditions under La Niña. This information can aid various decision-makers to make better use of seasonal climate predictions.

Keywords:

• Oceanic Niño Index (ONI)
• probability
• Standardised Precipitation Index (SPI)

Acknowledgements

Climate data supplied by the South African Weather Service (SAWS). The authors wish to extend their thanks to the Statistical Consultation Unit at the University of the Free State for their input.

Conflict of interest

The authors declare that they have no conflict of interest.