The analysis of 74 years of rainfall recorded by the Irwins on two farms south of Potchefstroom: technical note

Rainfall records for three rain gauges on the farm Limerick and three rain gauges on the farm Mealielands were recorded from 1924 until 1999 by Mr DJ Irwin and his son Mr NG Irwin. The observations from these two nests of rain gauges are used to analyse the trends in rainfall measurements over time and to analyse the correlation of rainfall measurements between these rain gauges. The results presented in this report highlight the fact that the observations of rainfall are different to one another in many cases, indicating that care should be taken when selecting a rain gauge to represent the rainfall over a particular area. Analysis of the annual totals of rainfall has also found that at least 15 years of observations are required to determine a representative MAP value. The analysis of the monthly rainfall data also indicates that the rainy season commences in November and ends towards the end of April. A study of the extreme daily rainfall events shows that many of the storms are localised and are confined to an area around the rain gauges. The length of the droughts on these two farms are not as long as the national figures which would indicate that more point rainfall estimates are required to understand fully the spatial extent of a drought. WaterSA Vol.27(4) 2001: 559-564