Changes in extreme daily rainfall characteristics in South Africa: 1921–2020

Abstract

Many areas in South Africa are prone to localized flooding. With climate change already said to affect the intensity of rainfall, there is a need to investigate if there is a change in the probability of significant to extreme daily rainfall across South Africa. This was investigated through the analysis of the daily time series of 70 manual rainfall stations, over the period 1921 to 2020. The analysis period was divided into two equal periods of 50 years for comparison. With the application of the gamma distribution, it is shown that most stations experienced an increase in the probability of receiving more than 50 mm per day, defined as significant rainfall, in the latter half of the analysis period. Also, most stations showed an increase in their 1:50- and 1:100-year return period values, with some stations over the eastern parts showing increases of over 100 mm. There was also an increase in the probability of “heavy rainfall” (>75 mm) and “very heavy rainfall” events (>115 mm) between the first and second half of the analysis period for most stations over the country when applying the Peak-Over-Threshold approach. In summary, the results indicate that, although the number of rain days has remained near-constant over the 1921–2020 period, the probability of experiencing significant and extreme daily rainfall events has increased generally for most regions in South Africa. This is of concern as rainfall of this nature can have serious consequences in terms of flooding, erosion, and damage to agriculture and infrastructure.

Keywords

• Daily rainfall
• Climate change
• Extremes
• Trends
• Variability
• Disaster risk reduction