The estimation of design rainfalls for South Africa using a regional scale invariant approach

Accurate estimates of design rainfall are essential inputs in water resource planning and engineering design. The duration of design rainfall which is required for design flood estimation may range from as short as 5 min for small urban catchments which have a rapid hydrological response, to a few days for large regional scale flood studies. In South Africa, as in many countries, the spatial density and record lengths of rainfall measured manually at daily intervals is far greater than rainfall recorded continuously. However, continuously recorded rainfall is needed to estimate design rainfall for durations shorter than 24 h. In this study, the scaling characteristics of extreme rainfall and a regional approach, based largely on the more reliable and abundant daily rainfall data, are utilised to estimate design rainfalls in South Africa for durations ranging from 5 min to 7 d. Key Words: Design rainfall, South Africa, Regionalisation, Scaling, Extreme rainfall, Rainfall probability WaterSA Vol.30(4) 2004: 435-44