Assessment of seasonal and annual rainfall trends and variability in South Africa

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dc.contributor.advisorDu Plessis, Kobus J. A.en_ZA
dc.contributor.authorKibii, Joshua Kiprotichen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.en_ZA
dc.date.accessioned2021-10-05T09:23:07Z
dc.date.accessioned2021-12-22T14:15:18Z
dc.date.available2021-10-05T09:23:07Z
dc.date.available2021-12-22T14:15:18Z
dc.date.issued2021-12
dc.descriptionThesis (MEng)--Stellenbosch University, 2021.en_ZA
dc.description.abstractENGLISH ABSTRACT: Weather variability, especially rainfall, receives significant global attention. The variability of rainfall distribution in time and space differs. Therefore, examining the trends and patterns of rainfall over South Africa, a water-scarce country, is important. A significant amount of research has been done both in South Africa and globally to find possible relationships between rainfall variability, seasonality, trends, and or climate change. This research was aimed at building on existing research of rainfall patterns in South Africa. The focus was on the use of non-parametric statistical analyses for trend analysis of recorded daily rainfall data (1900-2019), using 46 stations adequately distributed across South Africa. Absolute homogeneity tests were done and homogenous data characterised at monthly, seasonal and annual time steps. South Africa was divided into three rainfall regions: Summer, Winter and ‘All year’ rainfall regions. These regions were further categorised into eight climatic zones, based on SAWS climatic zones: North-Eastern Interior, KwaZulu-Natal, Western Interior, Central Interior, Southern Interior, North-Western Cape, South Western Cape and South Coast. Trend analysis was performed, and results indicated significant differences between daily, monthly, seasonal to annual time steps. The daily rainfall reflects insignificant trends. Monthly rainfall recorded statistically significant increasing trends in November, December, and January in the ‘All year’ and Summer rainfall regions and March, May, June and September recorded statistically significant decreasing trends in all three rainfall regions. The seasonal and annual trend analysis were performed for a long-term period of 120 years and three short-term periods of 40 years each. The short-term trends shift periodically within the three periods, resulting in only a few rainfall stations recording statistically significant long-term trends. The Summer rainfall region experienced alternating trends shifting across the three short-term periods towards an early or a late wet season with little change in mean annual rainfall. The Winter rainfall region had its main rainfall season becoming shorter, but wetter over the three short-term periods of analysis, while the ‘All year’ rainfall region experienced alternating shifts of dry and wet cycles with a slightly decreasing mean annual rainfall. In general, the seasonal rainfall trends of South Africa illustrated shorter, but more pronounced trends, progressively for the three short-term analysis periods. Only a marginal increase in annual rainfall was observed using the long-term analysis, while variability increased over the years, using the short-term analysis. The observed trends using non-parametric analysis do not have significant deviations from previous research outputs. However, the observed changes in rainfall were relatively low with a long-term increasing trend in annual rainfall of between 0.6 and1.0 mm during the analysis period of 120 years. This research, therefore, recommends that the use of projected rainfall (climate change) data in South Africa, should be well guided by considerations based on the observed rainfall data trends. Design and management decisions based on long-term rainfall projections due to climate change should be considered carefully, taking the design life of the infrastructure into consideration.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die wisselvallige weersomstandighede, veral reënval, geniet wêreldwyd beduidende aandag. Die wisselvalligheid van die verspreiding van reënval in tyd en ruimte verskil. Daarom is dit belangrik om die tendense en patrone van reënval oor Suid-Afrika, 'n waterskaars land, te ondersoek. 'n Aansienlike hoeveelheid navorsing is in Suid-Afrika en wêreldwyd gedoen om die moontlike verband tussen die wisselvalligheid van reënval, seisoenaliteit, tendense en of klimaatsverandering te vind. Hierdie navorsing het daarop gefokus om voort te bou op bestaande navorsing oor reënvalpatrone in Suid-Afrika. Die fokus was op die gebruik van nie-parametriese statistiese ontledings van historiese daaglikse reënvaldata (1900-2019) van 46 stasies, goed versprei oor Suid Afrika, om tendense te ondersoek. Absolute homogeniteitstoetse is gedoen en homogene data is gekarakteriseer vir maandelikse, seisoenale en jaarlikse tyd-stappe. Suid- Afrika is verdeel in drie reënvalstreke naamlik somer-, winter- en 'hele-jaar' reënvalstreke. Hierdie streke is volgens SAWB verder in agt klimaatsones ingedeel: Noord-Oostelike binneland, KwaZulu-Natal, Westelike-binneland, Sentrale binneland, Suidelike binneland, Noordwes-Kaap, Suidwes-Kaap en die Suidkus. Tendens ontledings is uitgevoer, en die resultate het beduidende verskille tussen daaglikse, maandelikse, seisoenale en jaarlikse tyd-stappe getoon. Die daaglikse reënval het nie enige beduidende tendense getoon nie. Maandelikse reënval het in November, Desember en Januarie in die somer- en 'heel-jaar'-reënvalstreke beduidende toenemende tendense en in Maart, Mei, Junie en September, beduidende dalende tendense in al drie reënvalstreke getoon. Die seisoenale en jaarlikse tendens ontledings is uitgevoer vir 'n langtermynperiode van 120 jaar en vir drie korttermynperiodes van 40 jaar elk. Die korttermyn tendense wissel oor die drie periodes, wat daartoe aanleiding gee dat slegs enkele reënvalstasies noemenswaardige langtermyn tendense getoon het. Die somerreënvalstreek het wisselende tendense getoon wat gedurende die drie korttermynperiodes gewissel het tussen 'n vroeër of 'n later nat seisoen met min verandering in die gemiddelde jaarlikse reënval. Die hoof reënvalseisoen van die winterreënvalstreek het korter en natter geword oor die drie korttermyn-ontledingsperiodes, terwyl die 'hele jaar' reënvalstreek wisselende verskuiwings tussen droë en nat siklusse ervaar het met 'n effense dalende gemiddelde jaarlikse reënval. In die algemeen het die seisoenale reënval tendense van Suid Afrika 'n toenemende korter, maar duideliker tendense, vir die drie korttermyn-ontledingsperiodes geïllustreer. Slegs 'n geringe toename in jaarlikse reënval is waargeneem met behulp van die langtermyn-ontleding, terwyl korttermyn-ontledings ʼn toename in wisselvalligheid oor die jare toon. Die waargenome tendense met behulp van nie-parametriese ontledings het nie beduidende afwykings van vorige navorsingsresultate getoon nie. Die waargenome veranderinge in reënval is egter relatief min, met ʼn langtermyn toenemende tendens van jaarlikse reënval wat wissel tussen 0.6 en 1.0 mm oor die ontledingsperiode van 120 jaar. Hierdie navorsing beveel dus aan dat die gebruik van reënval data soos voorspel deur klimaatsveranderinge, versigtig oorweeg moet word met inagneming van die waargenome reënval tendense. Ontwerp en bestuursbesluite gebaseer op vooruitskattings van langtermyn reënval as gevolg van klimaatsveranderinge, moet versigtig binne die konteks van die ontwerp- leeftyd van die infrastruktuur oorweeg word.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent138 pagesen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/123675
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectMann-Kendallen_ZA
dc.subjectFluctuations, Rainfallen_ZA
dc.subjectRainfall probabilitiesen_ZA
dc.subjectClimatic changesen_ZA
dc.subjectRainfall patterns -- South Africaen_ZA
dc.subjectUCTDen_ZA
dc.titleAssessment of seasonal and annual rainfall trends and variability in South Africaen_ZA
dc.typeThesisen_ZA
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