3 research outputs found
Assessment of seasonal and annual rainfall trends and variability in South Africa
Thesis (MEng)--Stellenbosch University, 2021.ENGLISH 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.AFRIKAANSE 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.Master
Application of Soil and Water Assessment Tool (SWAT) to Evaluate the Impact of Land Use and Climate Variability on the Kaptagat Catchment River Discharge
Water is life. It is an important element of the social and economic well-being of society. Kenya is a water-scarce country, ranked as 21st globally for the worst levels of water accessibility. The town of Eldoret is currently experiencing rapid population growth, resulting in ever-growing water demand. On the other hand, climate variability, land cover, and land use changes have altered the hydrologic response of the Kaptagat catchment, one of the major sources of water for Eldoret. This study uses the SWAT model in seeking to evaluate the impact of land use change and climate variability on the catchment yield, resulting in high variations in river flows and storage reservoir levels, and suggests possible mitigation measures to improve the yield. The model was customized for the study area, calibrated, and validated, and simulations were done to establish the changes in yield and river flow over time. This study observes that with time, land use changed due to increased settlement in the catchment, resulting in a decrease in forest cover (natural and planted) from approximately 37% in 1989 to 26% in 2019. Rainfall events also decreased but became more intense. The results of the changing land use and climate variability were changes in the catchment hydrologic response, occasioned by increased surface runoff and decreased baseflow and groundwater recharge, hence the high variations in water levels at the Elegirini and Two Rivers dams in the catchment during the dry and wet seasons, as modeled. The modeling of the catchment management scenarios indicates groundwater recharge increased by 17% and surface runoff decreased by 9%. Therefore, if the ongoing afforestation, reafforestation, and terracing practices by farmers (although small-scale) increasing vegetation cover in the catchment are adhered to, the catchment response regime will improve significantly with time, despite the increasing climatic variability
Application of Soil and Water Assessment Tool (SWAT) to Evaluate the Impact of Land Use and Climate Variability on the Kaptagat Catchment River Discharge
Water is life. It is an important element of the social and economic well-being of society. Kenya is a water-scarce country, ranked as 21st globally for the worst levels of water accessibility. The town of Eldoret is currently experiencing rapid population growth, resulting in ever-growing water demand. On the other hand, climate variability, land cover, and land use changes have altered the hydrologic response of the Kaptagat catchment, one of the major sources of water for Eldoret. This study uses the SWAT model in seeking to evaluate the impact of land use change and climate variability on the catchment yield, resulting in high variations in river flows and storage reservoir levels, and suggests possible mitigation measures to improve the yield. The model was customized for the study area, calibrated, and validated, and simulations were done to establish the changes in yield and river flow over time. This study observes that with time, land use changed due to increased settlement in the catchment, resulting in a decrease in forest cover (natural and planted) from approximately 37% in 1989 to 26% in 2019. Rainfall events also decreased but became more intense. The results of the changing land use and climate variability were changes in the catchment hydrologic response, occasioned by increased surface runoff and decreased baseflow and groundwater recharge, hence the high variations in water levels at the Elegirini and Two Rivers dams in the catchment during the dry and wet seasons, as modeled. The modeling of the catchment management scenarios indicates groundwater recharge increased by 17% and surface runoff decreased by 9%. Therefore, if the ongoing afforestation, reafforestation, and terracing practices by farmers (although small-scale) increasing vegetation cover in the catchment are adhered to, the catchment response regime will improve significantly with time, despite the increasing climatic variability