Abstract:
El Niño-Southern Oscillation (ENSO) plays an important role in the interannual variability
of rainfall in most parts of southern Africa. The effects of ENSO on the rainy season
characteristics and possible impacts on rainfed maize production were investigated. The rainy
season characteristics of concern are the onset of rains, cessation of rains, duration of rainy
season and seasonal rainfall total. 309 climate stations over the Free State Province with
rainfall data from 1950 to 2008 were analysed. The rainy season indices were further
subdivided into El Niño and La Niña years. The differences in averages of the rainy season
indices were determined for the negative phase of ENSO versus the overall averages and for
the positive phase of ENSO versus the overall averages. The results of the onset of rains
show no clear pattern in the Free State with some areas experiencing late onset and others
early onset in both El Niño and La Niña years. However, the cessation of rains occurs early
during the El Niño and late in La Niña years over most parts of the province. Consequently,
the duration of the rainy season is shorter than normal in El Niño years and longer than
normal in La Niña years. Seasonal rainfall is also lower than normal in El Niño years while in
La Niña years more cumulative rainfall in mostly observed. As a result, maize production is
favoured in La Niña years and reduction in production is normally observed during El Niño
years.
