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Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa
Thesis (MEng)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614066742132736 |
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| access_status_str | Open Access |
| author | Knoetzen, Rohan |
| author2 | Du Plessis, Kobus |
| author_browse | Du Plessis, Kobus Knoetzen, Rohan |
| author_facet | Du Plessis, Kobus Knoetzen, Rohan |
| author_sort | Knoetzen, Rohan |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134662 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:46:07.073Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134662 Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa Knoetzen, Rohan Du Plessis, Kobus Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. Rain and rainfall -- South Africa Climatic changes Greenhouse gas mitigation -- South Africa Thesis (MEng)--Stellenbosch University, 2025. Knoetzen, R. 2025. Investigating the Trends in the Magnitude and Frequency of Extreme Short-Duration Rainfall Depths in South Africa. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/cd6fe42f-2f99-478d-a974-33fef5bf1ece ENGLISH ABSTRACT: Extreme short-duration rainfall events pose significant economic, infrastructure and social challenges, yet limited research has investigated the trend in extreme short-duration rainfall in South Africa. This study, therefore, addresses this gap by examining the trends in the magnitude of extreme short-duration rainfall depths (MERD) and their frequency (FERD) across South Africa. The study aimed to determine the trends in MERD and FERD for storm durations ranging from 5 minutes to 24 hours at 18 rainfall stations spanning across all eight homogeneous rainfall zones in South Africa. The short-duration rainfall data were provided by the South African Weather Service, which underwent data quality control, gap filling, and homogeneity tests. The Annual Maximum Series (AMS) and Point Over Threshold Series (POT) were extracted for each storm duration to perform the trend analysis of the MERD and FERD, respectively. The POT series was extracted such that, on average, 3 to 5 annual exceedances occurred. Sub-hourly durations were analysed from 1994 to 2022, whereas at most stations, multi-hourly storm durations were analysed from 1983 to 2022. The trend analysis in this research was performed using the non-parametric Mann-Kendall and Sen’s Slope Estimator, with the robustness of the trends evaluated at significance levels of 1% (very strong), 5% (strong), 10% (moderate), 25% (weak) and 50% (very weak). In general, no dominant national trend direction was apparent as the statistically significant (very weak and very strong) trends occurred in similar proportions for both the MERD and FERD, 29% (27%) and 26% (30%) of the observations, respectively, displayed increasing (decreasing) trends. Although the most robust trends in both indices corresponded with more frequent increasing than decreasing trends, they represented only 8% and 10% of the observations during the MERD and FERD, respectively, indicating that the weak and explanatory trends appeared far more frequently. Regionally, the Western Interior displayed the most consistent increasing trends in both indices, highlighting the need for carefully reconsidering the stationarity assumptions in design rainfall estimates, as well as to prioritise regular maintenance of stormwater infrastructure in this region. By contrast, the most consistent decreasing trends in both indices were observed in the North Western Cape, indicating that the stationarity assumptions in design rainfall estimates are still appropriate within this region. In most regions, the current stationarity assumptions appear to be appropriate, as the weak and insignificant trends appeared more frequently. However, the presence of isolated robust increasing trends within several regions highlights the need for practitioners to make decisions based on station-specific rainfall data rather than regional generalisations. AFRIKAANSE OPSOMMING: Ekstreme kortduur-reënval gebeurtenisse hou beduidende ekonomiese, infrastruktuur en sosiale uitdagings in, tog is daar beperkte navorsing gedoen oor die tendense in ekstreme kortduur-reënval in Suid-Afrika. Hierdie studie spreek hierdie gaping aan deur die tendense in die grootte van ekstreme kortduur-reënvalhoeveelhede (MERD) en hul frekwensie (FERD) te ondersoek. Die studie mik om die tendense te bepaal in die MERD en FERD vir storm duurtes van 5 minute to 24 uur by 18 reënvalstasies wat span oor die agt homogene reënvalsones van Suid-Afrika. Die kortduurreënvaldata is deur die Suid-Afrikaanse Weerdiens verskaf wat gehaltebeheer, gapingsopvulling en homogeniteitstoetse ondergaan het. Die Jaarlikse Maksimumreeks (AMS) en die Punt-BoDrempelreeks (POT) is vir elke stormduurte ontrek om die tendensontleding van the MERD en FERD onderskeidelik uit te voer. Die POT is so opgestel dat daar gemiddeld 3 to 5 jaarlikse oorskrydings plaasgevind het. Sub-uur duurtes is oor die periode 1994 tot 2022 ontleed, terwyl by meeste statistes die mulit-uur duurtes van 1983 tot 2022 ontleed is. Die tendensontleding is uitgevoer met behulp van die nie-parametriese Mann-Kendall toets en Sen se Helling-skatting, met die sterkte van die tendense geëvalueer teen betekenisvlakke van 1% (baie sterk), 5% (sterk), 10% (matig), 25% (swak) en 50% (baie swak). In die algemeen was daar geen duidelike nasionale tendensrigting sigbaar nie, aangesien die statisties beduidende (baie swak en baie sterk) tendense in soortgelyke verhoudings voorgekom het. Tydens die MERD en FERD het onderskeidelik 29% (27%) en 26% (30%) van die waarnemings toenemende (afnemende) tendense getoon. Hoewel die sterkter tendense in beide indekse meer gereeld met toenemende as afnemende tendense ooreengestem het, het hulle slegs 8% en 10% van die waarnemings vir onderskeidelik die MERD en FERD verteenwoordig, wat aandui dat die swak en verklarende tendense meer algemeen voorgekom het. Op ‘n streekskaal het die Westelike Binneland die mees konsekwente toenemende tendense in beide indekse getoon, wat die behoefte beklemtoon om die aanname van stasionariteit in die ontwerp van reëvalberamings vestiging te herevalueer, asook om gereelde instandhouding van stormwater infrastruktuur in hierdie streek te prioritiseer. In kontras, is die mees konsekwente afnemende tendense in beide indekse in die Noord Wes-Kaap waargeneem, wat aandui dat die aanname van stasionariteit vir die ontwerp van reëvalberamings in hierdie streek steeds toepaslik is. In meeste streke blyk die huidige aanname van stasionariteit steeds gepas te wees, aangesien die swak en onbeduidende tendense meer gereeld voorgekom het. Nietemin beklemtoon die teenwoordigheid van geïsoleerde sterk toeneemde tendense in verkeie streke die belangrikheid om praktiese besluite te neem gebaseer op stasie-spesifieke reëvaldata eerder as op streeksveralgemenings. Masters 2025-12-22T11:53:40Z 2025-12-22T11:53:40Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134662 en Stellenbosch University xiv, 113 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Rain and rainfall -- South Africa Climatic changes Greenhouse gas mitigation -- South Africa Knoetzen, Rohan Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title | Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title_full | Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title_fullStr | Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title_full_unstemmed | Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title_short | Investigating the trends in the magnitude and frequency of extreme short-duration rainfall depths in South Africa |
| title_sort | investigating the trends in the magnitude and frequency of extreme short duration rainfall depths in south africa |
| topic | Rain and rainfall -- South Africa Climatic changes Greenhouse gas mitigation -- South Africa |
| url | https://scholar.sun.ac.za/handle/10019.1/134662 |
| work_keys_str_mv | AT knoetzenrohan investigatingthetrendsinthemagnitudeandfrequencyofextremeshortdurationrainfalldepthsinsouthafrica |