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The formulation of severity - duration - frequency relationships of drought events in South Africa
Thesis (MEng)--Stellenbosch University, 2023.
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| Language: | en_ZA en_ZA |
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867613911557079040 |
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| access_status_str | Open Access |
| author | Smith, Estee |
| author2 | Du Plessis, J. A. |
| author_browse | Du Plessis, J. A. Smith, Estee |
| author_facet | Du Plessis, J. A. Smith, Estee |
| author_sort | Smith, Estee |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/128813 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA en_ZA |
| last_indexed | 2026-06-10T12:43:40.048Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/128813 The formulation of severity - duration - frequency relationships of drought events in South Africa Smith, Estee Du Plessis, J. A. Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. Droughts -- South Africa Environmental indicators -- -- South Africa Conservation of natural resources -- South Africa Natural disasters -- South Africa Thesis (MEng)--Stellenbosch University, 2023. ENGLISH ABSTRACT: Drought severity-duration-frequency (SDF) relationships describe the cumulative deficit in precipitation or water availability over time, and are used to assess and visualise the severity and duration of drought events. SDF relationships of droughts are derived by accumulating and standardising the deficit in precipitation or water availability over a specific period, typically based on historical data, to provide a normalised measure of drought severity and duration. Drought indices can be employed to develop SDF curves by providing essential data on precipitation deficits or water scarcity, which are then standardised and cumulatively plotted to visualise the temporal patterns and severity of drought events. Numerous drought indices exist, and each is designed to capture specific aspects of drought conditions, making it essential to select the most appropriate index for a particular region or application. Drought indices rely on a variety of input data, including precipitation, temperature, soil moisture, and streamflow measurements, to assess and characterise drought conditions. Despite its significance and potential utility, South Africa currently lacks comprehensive countrywide SDF curves for drought assessment. The available data input sources in South Africa were assessed, and daily rainfall data from the South African Weather Service (SAWS) and Department of Water and Sanitation (DWS) were selected for analysis. The input data was assessed for minimum record length, record end date, percentage of missing data, homogeneity, and stationarity, and the basic statistics were calculated for each rainfall station. Rainfall stations with data that did not extend beyond the end of 2021, had a record length of less than 30 years, had more than 10% missing data, or displayed inhomogeneity or inadequate stationarity were excluded from analysis. Multiple drought indices were evaluated, and three were chosen for further analysis: the Percentage of Normal Precipitation (PNP), Deciles Drought Index (DDI), and Standardised Precipitation Index (SPI). Various timescales (3-, 6-, 12-, 24-, and 48-months) were computed for the three drought indices to evaluate data availability, particularly in scenarios where decision makers need to make informed decisions but the available data history is relatively short. For the SPI, three distributions (Weibull, Gamma and Log-normal) were examined and tested for goodness-of-fit, and the best-fit distribution was selected for each rainfall station. The development of SDF relationships is based on the use of the SPI. Data was extracted as Partial Duration Series (PDS) to ensure the independence of drought events. The SDF relationships are graphically presented as curves and spatial maps, facilitating a comprehensive assessment of drought severity, duration, and frequency. The results suggest that the DDI and PNP provide similar outcomes in terms of identifying the occurrence of drought events and assessing their duration over shorter timescales, making them viable options in South Africa, particularly when the precise severity of drought is not a primary concern. The SPI identified fewer droughts, but with an increased average drought duration compared to the DDI and PNP. The SDF curves generated from SPI offer valuable insights for when a detailed assessment of drought severity is of primary concern. AFRIKAANSE OPSOMMING: Die felheid, duurte en frekwensie van droogtes kan grafies voorgestel word met behulp van SDF-kurwes. SDF-kurwes beskryf die kumulatiewe tekort aan reënval of waterbeskikbaarheid oor tyd en word gebruik om die felheid en duurte van droogtegebeure te beoordeel en te visualiseer. SDF-verhoudings van droogtes word ontwikkel deur die tekort aan reënval of waterbeskikbaarheid oor ʼn spesifieke tydperk te bepaal en te normaliseer, gewoonlik gebaseer op historiese data, om ʼn gestandaardiseerde maatstaf van die felheid en duurte van ʼn droogte te bepaal. Droogte-indekse kan gebruik word om SDF-kurwes te ontwikkel wat noodsaaklike inligting voorsien oor ʼn beperking op reënval of watervoorsiening, wat dan gestandaardiseer en opgetel word om die tydpatrone en felheid van droogtegebeure te visualiseer. Talle droogte-indekse bestaan, elk ontwerp om spesifieke aspekte van droogtetoestande vas te vang – wat dit noodsaaklik maak om die mees toepaslike indeks vir ʼn spesifieke streek of toepassing te kies. Droogte-indekse steun op ʼn verskeidenheid van data, insluitend reënval, temperatuur, grondvogtigheid, en stroomvloeimetings, om droogtetoestande te beoordeel en te karakteriseer. Ondanks die belangrikheid en potensiële nut ontbreek daar tans ʼn omvattende, landswye SDF-kurwe vir droogte-ontleding in Suid-Afrika. Suid-Afrikaanse data was ontleed uit beskikbare databronne, en vir hierdie navorsing is daaglikse reënvaldata van die Suid-Afrikaanse Weerdienste (SAWS) en die Departement van Water en Sanitasie (DWS) gebruik vir ontleding. Die data was beoordeel vir ʼn minimum rekordlengte, einddatum, persentasie van ontbrekende data, homogeniteit en stationariteit, en eenvoudige statistiek was bereken vir elke reënvalstasie. Reënvalstasies met data wat nie tot die einde van 2021 gestrek het nie, ʼn rekordlengte van minder as 30 jaar gehad het, meer as 10% ontbreekte data gehad het, of probleme van nie-homogeniteit of nie-stationariteit getoon het, was uitgesluit van die ontleding. Verskeie droogte-indekse was geëvalueer, en drie daarvan is gekies vir verdere analise, wat die Persentasie van Normale Reënval (PNP), Persentiel Droogte-indeks (DDI), en die Gestandaardiseerde Reënvalindeks (SPI) insluit. Die drie droogte-indekse is bereken vir verskeie tydskale (3-, 6-, 12-, 24- en 48-maande) om databeskikbaarheid te evalueer, veral in situasies waar besluitnemers ingeligte besluite moet neem, veral waar die beskikbare data beperk is. Vir die SPI is drie verdelings (Weibull, Gamma en Log-normaal) ondersoek en die statistiese passing bereken, en die verdeling met die beste passing is vir elke reënvalstasie gekies. Die SPI data was gebruik om die SDF-verhoudings te ontwikkel. In die frekwensie-ontleding van die SDF-verhoudings is data onttrek deur gebruik te maak van ʼn Gedeeltelike Duurte-reeks (PDS) om die onafhanklikheid van droogtegebeure te verseker. Die SDF-verhoudings was grafies voorgestel as kurwes en ruimtelike kaarte, wat ʼn omvattende beoordeling van felheid, duurte en frekwensie vergemaklik. Die resultate dui daarop dat die DDI en die PNP vergelykbare resultate lewer met betrekking tot die identifisering van die frekwensie van droogtegebeure en die bepaling van hul duurte vir kortertermyndroogtes, wat dit gepaste opsies maak in Suid-Afrika, veral wanneer die presiese felheid van droogte nie ʼn primêre bekommernis is nie. Die SPI het minder droogtes geïdentifiseer, maar met ʼn verhoogde gemiddelde droogteduur in vergelyking met die DDI en die PNP. Die SDF-kurwes wat uit die SPI gegenereer is, bied waardevolle insigte wanneer ʼn gedetailleerde assessering van droogte felheid van primêre belang is. Masters 2023-11-29T03:44:58Z 2024-01-08T12:04:01Z 2023-11-29T03:44:58Z 2024-01-08T12:04:01Z 2023-12 Thesis https://scholar.sun.ac.za/handle/10019.1/128813 en_ZA en_ZA Stellenbosch University xix, 228, 2 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Droughts -- South Africa Environmental indicators -- -- South Africa Conservation of natural resources -- South Africa Natural disasters -- South Africa Smith, Estee The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title | The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title_full | The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title_fullStr | The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title_full_unstemmed | The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title_short | The formulation of severity - duration - frequency relationships of drought events in South Africa |
| title_sort | formulation of severity duration frequency relationships of drought events in south africa |
| topic | Droughts -- South Africa Environmental indicators -- -- South Africa Conservation of natural resources -- South Africa Natural disasters -- South Africa |
| url | https://scholar.sun.ac.za/handle/10019.1/128813 |
| work_keys_str_mv | AT smithestee theformulationofseveritydurationfrequencyrelationshipsofdroughteventsinsouthafrica AT smithestee formulationofseveritydurationfrequencyrelationshipsofdroughteventsinsouthafrica |