Extreme indices developed by the World Meteorological Organization (WMO) Expert Team on Climate Change Detection and Indices (ETCCDI) provide an understanding of how climate extreme (temperature and rainfall) have changed over time.
A total of 27 weather stations was used for temperature trends analysis spanning the period 1931-2015. For rainfall, a total of 60 weather stations were used for the rainfall trend analysis spanning the period 1921-2015. The base period, from which the annual index values of all indices are determined (except the annual maxima and minima) was selected as 1981 – 2010, which can be considered to be the present general norm for similar trend studies. The trends were tested for significance at the 95% confidence level.
Associated increases in the annual number of hot days have also occurred, but there have been decreases in the annual number of cold nights over most of the country. There is strong evidence of statistically significant increases in rainfall occurring over the southern interior regions, extending from the western interior of the Eastern Cape and eastern interior of the Western Cape northwards into the central interior region of the Northern Cape, over the period 1921-2015.
Extreme daily rainfall events have increased over these same areas, with these increases also being statistically significant and extending northwards into North West, the Free State, and Gauteng. Over Limpopo, there is strong evidence of statistically significant decreases in annual rainfall totals.