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Population dynamics of the Zuurberg Cycad and the predicted impact of climate changeSingh, Karishma January 2012 (has links)
Cycads first appeared about 300 million years ago and historical data indicates that they survived fluctuations of global temperature and carbon dioxide concentrations and reached peak abundance during periods where temperature and carbon dioxide concentrations were much higher than the present conditions as well as the predicted increased levels. With Africa being one of the most vulnerable regions to climate change and in the absence of an evaluation of predicted impacts of climate change on cycads, this study aims to contribute to our understanding of responses of Encephalartos longifolius to increased temperature. Encephalartos longifolius (Jacq.) Lehm is an Eastern Cape endemic and like most cycads has been around for millions of years with very little change to its basic structure. Photosynthetic rates showed E.longifolius seedlings have C3 photosynthesis and even under stress they do not switch over to CAM photosynthesis. The photosynthetic rates of seedlings showed a typical C3 -plant type response under elevated carbon dioxide levels. Increased temperatures could be detrimental to the species but coupled with elevated carbon dioxide levels the growth of Encephalartos longifolius are postulated to outweigh the negative impacts of increased temperatures. Whilst climatic conditions in the Eastern Cape might not impact the abundance of Encephalartos longifolius, the species however is declining rapidly to the present near-threatened status. Demographic studies revealed a high percentage of juvenile numbers in the wild; however juvenile plants are impacted on by animals thereby jeopardizing their survival. Adult plants are heavily impacted on by animals; this reduces the probability of new offspring being produced. Cycads are also very slow - growing which is the primary cause of their ruin in the wild. Encephalartos longifolius grows at just over approximately 1 cm per year with growth being more rapid in the juvenile plants. Once juvenile plants reach approximately 60 cm they stop growing in diameter but only get taller. Seed germination is also a very slow process with an optimum temperature of 28°C and a growth medium of at least 50 percent moisture. Regardless of the Eastern Cape predicted to become the hottest province in South Africa as a result of climate change, cycads will be able to adapt to the changing environment and conservation plans should focus on animal and human impacts that are the major force causing decreasing abundance of Encephalartos longifolius in the wild.
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The influence of climate change on short duration rainfall in the Western CapeBurger, Gysbertus Johannes 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The Western Cape has been subject to extreme rainfall storms in the last decade, which has
been responsible for millions of Rands worth of damage to public infrastructure and human
settlements. Current climate model projections under climate change suggest that the Western
Cape can expect greater rainfall intensities, with magnitude of rainfall events increasing, but the
frequency of occurrence of events decreasing. The aim of this research is to assess if historical
short duration rainfall data provides any evidence to support increasing intensities in rainfall in
the Western Cape.
Short duration rainfall data (< 24 hours), consisting of digitised autographic- and automatic
weather station data (AWS), was selected from the South African Weather Services’ database
for the Western Cape and wider South African region, in order to combine the data for an
extension of the effective record length. Numerous difficulties were encountered with the data
that required the application of editing and quality control procedures. The digitised autographic
data contained many errors and generally compared poorly to standard gauge daily rainfall
totals of the same period. After the application of editing and quality control procedures, seven
stations were selected and their autographic and AWS data was combined for further detailed
analysis. Analysis was divided into two sections, one for the analysis of the magnitude of the rainfall,
the other for the frequency of occurrence of rainfall events. For the magnitude analysis, nonstationary
extreme value theory was applied by implementing a parametric and non-parametric
non-stationary approach to both the generalised extreme value distribution (GEV) with an annual
maximum series, and a generalised Pareto distribution with a peaks over threshold series.
The parametric approach entailed fitting linear models to the parameters of the extreme value
distributions, and the non-parametric approach tested if return levels of the distributions remained
constant over a moving window period. The frequency analysis entailed the recording
of the annual number of rainfall events exceeding predetermined threshold values.
For the magnitude analysis, the parametric approach only produced two stations with significant
non-stationarity and only for the GEV, whilst the non-stationary approach produced results that
can indicate non-parametric behaviour, but this was most likely because of the combination of
autographic and AWS data. The frequency analysis produced results that indicated no observable
results for some stations, while others produced trends that are consistent with a change
from the autographic to AWS data.
This lead to the conclusion that with the available data, no clear or significant evidence supporting
increasing intensities or any other change in short duration rainfall was found regarding the
magnitude and frequency of occurrence of rainfall events. / AFRIKAANSE OPSOMMING: The Wes-Kaap het die afgelope dekade deur uiterse storms deurgeloop wat miljone Rande se
skade aan publieke infrastruktuur en nedersettings veroorsaak het. Huidige klimaatsmodel resultate
wat klimaatsverandering inkorporeer, beraam dat die Wes-Kaap hoër reënvalintensiteite
kan verwag, waar die grootte van die en reënvalgebeurtenisse toeneem, maar die frekwensie van
die reënvalgebeurtenisse afneem. Die doel van hierdie navorsing is om te bepaal of historiese
kortduurtereënvaldata in die Wes-Kaap enige toenemende reënvalintensiteite aandui.
Kortduurtereënvaldata (< 24 uur) wat uit versyferde autografiese- en automatiese weerstasie
(AWS) data bestaan, was uit die Suid Afrikaanse Weerdienste se databasis gekies vir stasies in
dieWes-Kaap en die wyer Suid Afrikaanse gebied, sodoende om die effektiewe rekordlengte te
verleng. Redigering- en kwaliteitsbeheerprosudures moes toegepas word na ’n aantal probleme
met die data ontdek was. Die versyferde autografiese data het baie foute bevat en oor die
algemeen swak vergelyk met die standaard daaglikse totaalmetings van dieselfde periode. Na
die redigering- en kwaliteitsbeheerprosudures toegepas was, was sewe stasies gekies en hul
autografiese en AWS data was saamgestel vir verdere analise. Die analise het uit twee afdelings bestaan: die analise van die grootte van die reënvalgebeurtenisse,
en die frekwensie van die reënvalgebeurtenisse. Nie-stasionêre ekstreemwaardeteorie
was toegepas op die grootte van die reënvalgebeurtenisse deur gebruik te maak van parametriese
en nie-parametriese nie-stasionêre metodiek. Die veralgemeende ekstreemwaardeverdeling
(AEW) met ’n jaarlikse maksimum reeks, en die veralgemeende Paretoverdeling met ’n
pieke bo drempelwaarde reeks was gebruik. Die parametriese metode het bestaan uit die passing
van lineêre modelle aan die parameters van die estreemwaardeverdelings. Die nie-parametriese
metode het getoets of die terugkeervlakke van die verdelings konstant gebly het oor ’n bewegende
vensterperiode. The frekwensie analise het bestaan uit die aantekening van die jaarlikse
reënvalgebeurtenisse wat bepaalde drempelwaardes oorskry.
Die parametriese metode het net twee beduidende nie-stasionêre staties opgelewer, uitsluitlik
vir die AEW. Die nie-parametriese metode het resultate gegenereer wat moontlike niestasionarieit
aandui, maar dit is heel moontlik as gevolg van die samestelling van die autografiesen
AWS data. Die frekwensie analise het óf geen sigbare neiging vir die resultate vir ván stasies
gegenereer nie, óf het resultate gegenereer wat aandui op die samestelling van die autografiesen
AWS data.
Dit het tot die gevolgtrekking gelei dat daar geen aanduiding in die kortduurtereënvaldata
bestaan wat toenemende reënvalintensiteite ondersteun nie vir beide die grootte en frekwensie
van reënvalgebeurtenisse.
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Variability and long-term trends of climate extremes over the Limpopo, South AfricaSikhwari, Thendo 20 September 2019 (has links)
MENVSC / Department of Geography and Geo-Information Sciences / Climate change has a crucial impact on livelihoods, economy, and water resources
due to the occurrence of weather and climate extreme events such as floods, droughts
and heat waves. Extreme weather has been increasing worldwide, hence the need to
understand their nature and trends. The aim of this study was to analyse the spatial
variability and long-term trends of climate extremes over the Limpopo in South Africa
from 1960 to 2014. Rainfall, temperature, and circulation fields were analysed to
understand the extent, nature of climate extremes over the Limpopo. Extreme value
theory (EVT) is a powerful method that was also employed in this study to provide
statistical models for events rarely observed. R statistical software was used for
clustering analysis which has a variety of functions for cluster analysis. Any station
whose value is larger than 95th for any day of the season was considered as a
widespread extreme event. The results show that the study area is highly vulnerable
to extreme events due to its latitudinal location and low altitude. Anomalous cut-off
lows, tropical cyclones and tropical storms are the major extreme producing systems
affecting the Limpopo province whilst the Botswana High becomes dominant during
heat waves and drought. Extreme weather events are common in Limpopo during
summertime and often coincide with mature phases of the El Nino Southern
Oscillation. In this study, after the suitable model for data was chosen, the interest was
in deriving return levels of extreme maximum rainfall. The computed data for return
levels predicted that the 5-year return period’s return level is approximately 223.89
mm, which suggests that rainfall of 223.89 mm or more per month should occur at that
station or location on the average of once every five years. / NRF / http://hdl.handle.net/11602/1485
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Assessing the impacts of climate change and adaptation strategies on smallholder farming in the Vhembe District, South AfricaKom, Zongho January 2020 (has links)
PhD (Geography) / Department of Geography and Geo- Information Sciences / One of the major challenges facing all categories of farmers globally is climate change. African smallholder farmers are the most vulnerable to changes in climate. In most parts of South Africa, empirical evidence indicates the level to which climate change has impacted negatively on agricultural production. Rising temperatures, prolonged drought and decreasing rainfall have affected local farmers’ livelihood and crop production. In the Vhembe District of South Africa’s Limpopo Province, smallholder farming predominates and its vulnerability to climate change has increased for the past decades. This study, therefore, assesses the impact of climate change and adaptation strategies on smallholder farming systems in the Vhembe District To achieve this aim, qualitative and quantitative research methodologies were employed. A questionnaire was administered to a sample of 224 smallholder farmers to elicit data on perceptions; climate change impacts, adaptation and IKS based strategies to deal with climatic shocks. Focus group discussions (FGDs), semi-structured interviews with the extension officers elicited thematic data that complemented the interview survey. Climate data were obtained from the South Africa Weather Service (SAWS) for the period 1980 to 2015. Smallholder farmers’ perceptions about climate change were validated by an analysis of climatic trends from 1980-2015. A thematic analysis of qualitative data and the Multi Nominal Logit (MNL) regression model was used based on socio-economic and biophysical attributes such as access to climate knowledge, gender, farm size, education level, and farmers’ experience, decreasing rainfall and increasing temperature as farmers’ determinants of their adaptation options to climate change. Furthermore, farmers’ perceptions tallied well with climatic trends that showed flood and drought cycles. Most of the smallholder farmers were aware of climate change and its impacts over the past decades. The study further indicated that, due to the marked climate change over this period, farmers have adopted different coping strategies at on-farm and off-farm levels. In terms of adaptation, the major adaptive strategies used by smallholder farmers included the use of drought-tolerant seeds; planting of short-seasoned crops; crop diversification; changing planting dates; irrigation and migrating to urban areas. The study recommends a framework that would include water conservation (rainfall harvesting); investment in irrigation schemes and other smart technologies that integrate indigenous knowledge systems and modern scientific knowledge to enhance crop production. / NRF
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