Updating the estimation of 1-day probable maximum precipitation in South Africa

Abstract

Study regionSouth Africa Study focusThe Probable Maximum Precipitation (PMP) is the theoretical upper limit of extreme rainfall and is widely used by engineers and hydrologists to determine the Probable Maximum Flood (PMF) which is critical for the design and risk management of high-hazard hydraulic structures. In South Africa, the PMP was last estimated over 50 years ago using approximately 30 years of data. Since then numerous severe rainfall events have occurred which exceed presently available PMP estimates. Despite this, the outdated estimates are currently used in professional practice. In addition, modernised methods have been developed and applied globally to estimate the PMP, highlighting the need to update the PMP estimates for South Africa. This paper aims to present updated and modernised PMPs for the country. New hydrological insights for the regionUsing updated rainfall records and a storm maximisation and transposition approach, this paper provides new 1-day PMP estimates for the country. The importance of revising the PMP to include new extreme rainfall events is highlighted as the majority of the events used in this study occurred after the publication of the previous estimates. The use of extended rainfall records and modernised methods produces generally larger PMP estimates compared to the previous estimates and continual revision of the PMP is recommend to include new extreme rainfall events.