Doctoral Degrees (Geography and Environmental Studies)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/617

Browse

Now showing 1 - 5 of 50

The influence of topographical variability on wildfire occurrence and propagation
(Stellenbosch : Stellenbosch University, 2024-03) Christ, Sven; De Klerk, Helen; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
ENGLISH ABSTRACT: Wildfires have increasingly become a point of concern, especially with notable incidents like the 2017 Knysna fire. These naturally occurring phenomena, despite their disruptive nature, are crucial for the sustainability of certain ecosystems. At the heart of understanding wild-fires lies the relationship between climate, vegetation, topography, and human land use, with topography standing out as a significant determinant. This thesis delves into the fundamen-tal role of topography, emphasizing its effect on the ignition, propagation, and behaviour of wildfires. Utilizing Digital Elevation Models (DEMs), the research extracts invaluable topographic data aiming to augment the understanding of wildfires, especially in mixed natural forest and fyn-bos ecosystems. Existing fire models have shown certain shortcomings, often overlooking crucial localized wind data, which has profound implications for predicting fire behaviour. By bridging this gap, the study explores the potential of computational fluid dynamics in modelling surface winds based on topography for fire research. The research systematically addresses several key objectives: Mapping the current land-scape of topography-cantered wildfire research and investigating the utility of DEM-derived surface wind in refining fire propagation models, identifying and analysing historical fire patterns to pinpoint fire refugia in the Knysna/Tsitsikhama region, employing machine learning techniques, to determine if topographic variables extracted from DEMs can antici-pate fire refugia. The findings underscore the salience of topography in wildfires. Especially significant is the role of aspect in determining fire refugia, emphasizing that a combination of multiple variables offers the most accurate insights. Machine learning, notably the XGBoost model, showcases potential in identifying critical topographical features impacting fire behaviours. Furthermore, the research sheds light on the pivotal influence of wind chan-nels, formed by topographical features, in both the inception and spread of wildfires. In summary, this thesis underscores the integral role of topography in understanding wild-fires. It charts a roadmap for future research, emphasizing the importance of high-quality validation data, a more comprehensive mapping of fire refugia, and an acknowledgement of the influence of human activity on fire regimes. By building on the methodologies and in-sights presented, there lies an opportunity to advance sustainable wildfire management so-lutions that benefit both ecosystems and human communities.
A multi-scale study of wind erosion susceptibility along the South African Wild Coast
(Stellenbosch : Stellenbosch University, 2024-03) Singh, Rebekah Gereldene; Kemp, Jaco; Botha, Greg; Stellenbosch University. Faculty of Arts and Social Sciences. Dept of Geography and Environmental Studies.
ENGLISH ABSTRACT: Wind erosion is a significant driver of land degradation, affecting over a third of all land areas in recent centuries. Accelerated wind erosion in South Africa has caused severe localised land degradation, similar to that observed in parts of the ecologically important Wild Coast region. This erosion-induced degradation has led to localised desertification and poses risks to vulnerable wetland and river ecosystems. In data-sparse regions such as the Wild Coast, identifying highly susceptible areas becomes crucial to mitigate the detrimental effects of accelerated wind erosion. This study aims to determine the spatial distribution of wind erosion features along the Wild Coast, investigate factors influencing their occurrence and growth, and model the area's future susceptibility to wind erosion. Historical aerial photography, Google EarthTM imagery, and multi-temporal mapping spanning an 85-year period were utilised to create a wind erosion inventory map. It revealed an uneven spatial distribution of wind erosion sites, primarily clustered within a 2 km stretch along the coastal study area. These sites were concentrated in specific locations such as Xolobeni, Mkambati, Mngazi River Mouth - Noxova - Mbolompo Point, Wavecrest, and Kei River Mouth. Human activities in wind-exposed areas, such as disturbed agricultural fields, bare patches in grasslands, informal sand mines, and tracks, were identified as the key locations where these features initiated. Over the 85-year period, some erosion features expanded significantly, while others remained relatively stable due to the establishment of peripheral vegetation that acts as wind barriers. Long-term remote sensing analyses focused on the Xolobeni area, a representative subset of the broader Eastern Cape Wild Coast study region, aimed to comprehend the influence of long-term changes in land cover, vegetation status, soil texture, and soil moisture conditions on the occurrence and evolution of wind erosion features. This analysis utilised multi-temporal Landsat 5 Thematic Mapper (L5 TM) and Landsat 8 Operational Land Imager (OLI) imagery covering the period from 1987 to 2020, in conjunction with available topographical data from 1982, 1993, and 2004. The application of the Random Forest classifier successfully mapped land cover for the years 1987, 1991, 1999, 2004, 2010, 2015, and 2020, achieving overall accuracies exceeding 80.00% and Kappa indices surpassing 0.77 for each of these seven years. A primary finding of the land cover change assessment reveals the susceptibility of degraded grasslands to wind erosion and noted a rapid expansion of wind erosion features between 1987 and 1999, followed by a subsequent period of stability. The analysis of computed time-series Normalised Difference Vegetation Index (NDVI), Topsoil Grain Size Index (TGSI), and Normalised Difference Moisture Index (NDMI) data revealed that regions impacted by wind erosion consistently exhibited lower NDVI values, indicating reduced vegetation cover conditions, reaffirming the influence of vegetation on wind erosion development. Higher TGSI values denoted areas associated with higher wind erosion susceptibility and emphasised the significance of sandy soils with reduced clay content in erosion vulnerability. Lower NDMI values associated with affected regions highlighted that drier soil conditions promote wind erosion processes. The multi-temporal analyses of topographical data revealed that abandoned cultivated lands and zones with high track density were prone to erosion, highlighting a connection between human activities and wind erosion susceptibility in the study region. General concepts of the Wind Erosion Equation were adopted in this study to map the regional wind erosion susceptibility conditions. Two regional susceptibility methods were implemented and compared. Model 1 employed a geostatistical approach, based on erosion factor class frequency ratio data and Analytical Hierarchy Process importance weights. Model 2 utilised the data-driven Weights of Evidence modeling technique. Model 1 classified large areas of the study area as having low susceptibility (46%), while Model 2 classified more than 90% of the areas as very low susceptible zones. Both models show that less than 4% of the study region has a high to very high susceptibility to wind erosion. In general, areas associated with higher wind erosion susceptibility are poorly vegetated, wind-exposed coastal zones characterised by unconsolidated, erodible sandy soils. Model 1 and Model 2 are associated with area under the receiver operating characteristic curve values of 0.987 and 0.946, respectively, displaying satisfactory average performances. Recommendations for combating wind erosion along the ecologically sensitive Wild Coast include avoiding wind-aligned trackways, protecting existing vegetation, minimising bare soil patches in vulnerable areas, and establishing indigenous vegetation barriers. Utilisation of the developed wind erosion inventory and susceptibility maps will aid stakeholders in developing targeted conservation strategies required to shield vulnerable regions from further degradation.
Earth observation methods for sustainable Karoo Rangeland Management
(Stellenbosch : Stellenbosch University, 2023-12) Harmse, Christiaan Johannes; Van Niekerk, Adriaan; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
ENGLISH ABSTRACT: Rangelands, which comprise 25% of the earth's land surface, are under severe pressure due to the increasing global environmental problem of rangeland degradation. Ecological rangeland studies aim to determine the condition and productivity of rangelands and the severity of their degradation. In situ assessments are considered the most accurate way of monitoring rangeland degradation, but they are expensive and time-consuming, particularly when carried out over large areas. The Nama-Karoo biome in Southern Africa is primarily used for sheep and goat farming and is at risk of being overgrazed. Rangeland monitoring aims to determine whether grazing management strategies meet the goals of sustainable resource utilisation. Three experiments involving the combination of Earth observation technologies for rangeland monitoring were carried out in this research. First, a hypothesis that sheep graze more selectively under low stocking rates – potentially resulting in localised overgrazing – was tested. Livestock tracking, in situ observations, and Sentinel-2 imagery were used to make rangeland-scale observations of sheep grazing behaviour and vegetation conditions in the Nama-Karoo. The results showed that livestock congregates along drainage lines with deeper soil depth. There was a clear difference in the use of grazing areas among different stocking density classes. The conclusion was that spatial analyses of remotely sensed data can provide a landscape-scale overview of livestock movement patterns; and that high-resolution normalised difference vegetation index (NDVI) data can be used as a grazing management tool to determine the spatial variability of productive areas across the semiarid Upper Karoo rangelands and identify preferred grazing areas. Monitoring animal weight gain is expensive and often involves rounding up animals over large areas and long distances, leading to stress-related health problems and weight loss in animals. The second experiment evaluated remotely sensed vegetation indices for modelling sheep weight gain in semi-arid rangelands. The experiment also analysed the grazing behaviours in relation to time and location by using Sentinel-2 imagery and sheep movement data obtained from global positioning system (GPS) collar receivers. The results show that the average daily distance covered by sheep remained consistent throughout the year. The study successfully demonstrated the predictive capability of the NDVI in determining changes in the weight of sheep. The third experiment evaluated the effectiveness of multispectral (MS) and hyperspectral (HS) remotely sensed, unmanned aerial vehicle-(UAV)-based data and machine learning (random forest) methods to differentiate between 15 dominant Nama-Karoo plant species to aid ecological impact surveys. The results show that MS imagery was unsuitable as classification accuracies were generally low (37.5%). However, higher classification accuracies (>70.0%) were achieved when HS imagery was employed. Using in situ spectroscopic data collected with a fieldspectroradiometer, 12 key wavelengths were identified for discriminating among the dominant Karoo plant species with accuracies exceeding 90%. Reducing the dimensionality of the in situ spectroscopic dataset to the 12 key bands increased classification accuracies from 84.8% (all bands) to 91.7% (12 bands). Although classification accuracies were comparatively lower (76%) when HS remotely sensed imagery was used (instead of the in situ spectroscopic data), the results indicate that HS remote sensing imaging has the capability to effectively map indicator plant species in the Karoo region. The techniques developed in this research can be used to carry out satellite and UAV-based ecological assessments over large and inaccessible areas, assisting in managing the extensive Karoo rangelands more sustainably.
Adverse impacts of agricultural expansion on hydrological and nutrient dynamics in a Renosterveld landscape – can natural vegetation offer solutions
(Stellenbosch : Stellenbosch University, 2023-03) De Waal, Jan; Van Niekerk, Adriaan, 1970-; Miller, J; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
ENGLISH ABSTRACT: Agricultural systems deliver a range of products to human society including, food, fuel, textiles and pharmaceuticals. However, the global expansion of agricultural activities has resulted in several negative outcomes such as biodiversity loss, increased carbon emissions, topsoil erosion and water pollution. Thus, the degradation of natural landscapes due to agricultural transformation has resulted in a loss of ecosystem services over time by increasing habitat loss, nutrient movement, sedimentation of rivers and pesticide poisoning in non-target species. One of the most impacted landscapes in terms of agricultural transformation in South Africa is renosterveld vegetation. Lowland renosterveld is a small-leaved, evergreen shrubland found on the shale-rich, fertile soils of the south-western Cape of South Africa where it forms part of the Fynbos biome, a species-rich floral kingdom. Renosterveld typically occurs on fine-grained, clay-rich soils as opposed to the sandy, nutrient-poor soils on which fynbos is located. Agricultural expansion has resulted in the destruction of the indigenous renosterveld vegetation which now exhibits a great degree of fragmentation. This dissertation documents an investigation of the impact of agricultural expansion on the hydrological, sediment and water quality dynamics in the Overberg renosterveld landscape in theWestern Cape. An evaluation is reported of whether conservation of this threatened vegetation can allow for the delivery of ecosystem services in vegetation buffers in terms of phytoremediation of nutrient inputs from agricultural slopes. The impact of changing landuse on hydrological characteristics of the area at a landscape level is examined first, followed by a case study of the Bot River by implementing a fully differentiated hydrological model with a sediment delivery component. Results confirm that hydrology on a landscape level has been greatly impacted by changes in landuse, while modelled soil erosion from the Bot River catchment depicts an increase in soil erosion from 22 t/km2/year under natural conditions to 490 t/km2/year under 2018 landuse. A one-year monitoring programme of the river was undertaken to evaluate changing dissolved nutrient dynamics down the river’s long profile through the use of ion-chromatography and stable isotope analysis. The results of this analysis indicate that nutrient loading in the river is linked to agricultural landuses and that NO[x]-N levels in the river vary seasonally and periodically exceed water quality guidelines for aquatic ecosystems. Finally, an assessment was made of the potential for natural vegetation buffer strips to mitigate nutrient inputs from agricultural hillslopes. This was performed by an analysis of soil samples via inductively coupled plasma atomic emission spectroscopy (ICP-AES), laboratory-based testing for bio-available phosphorus, nitrate and ammonium as well as isotope ratio mass spectrometer (IRMS) testing of N and C isotopic composition in soils. Results show that N concentrations in cultivated field and renosterveld soils are impacted by fertilisation of agricultural lands. There is significantly (p <0.05) more P in cultivated fields than in renosteveld soils, while renosterveld soils have a significantly (p <0.05) higher C content than cultivated fields, thus acting as a valuable carbon sink. Renosterveld fragments are shown to remediate polluted agricultural runoff, and so provide a valuable ecosystem service in the landscape.
A chaos theory approach to understanding the impact of the COVID-19 pandemic on tourism businesses in Plateau State, Nigeria
(Stellenbosch : Stellenbosch University, 2022-12) Iirmdu, Tina Odinakachi; Donaldson, S. E.; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
ENGLISH ABSTRACT: Nations worldwide are grappling with the challenges of crises and disasters affecting the tourism industry. The coronavirus (COVID-19) which unexpectedly broke out in 2019 in Wuhan, China spread around the world in 2020, paralyzing tourism businesses. Previous crisis impact management strategies in tourism have relied heavily on linear deterministic models, which are incapable of considering the complex and chaotic nature of the tourism system. The use of chaos theory for crisis management in the tourism industry during the pandemic is still an emerging field that is yet to be fully explored. This study helps bridge this knowledge gap by using chaos theory to investigate the impact of the COVID-19 pandemic on tourism businesses in the Plateau State of Nigeria. A pragmatic mixed-method inductive research approach was followed in this study. This approach made it possible to obtain valid and reliable data by conducting semi-structured interviews and a questionnaire survey as the primary data collection techniques. A total of 24 semi-structured interviews were conducted with the managers and owners of tourism businesses to gather information on the business management practices and risk management strategies they used during the health crisis. In addition, tourism business managers completed a total of 227 questionnaires on the impact of the pandemic on their businesses, while 408 tourists completed the questionnaire on their experiences during the pandemic. The information from the semi-structured interviews was thematically analyzed and descriptive statistics were used to examine questionnaire survey data. Findings about the tourists’ experiences during the pandemic show that non-pharmaceutical interventions have changed tourism practices and tourist behaviour. The pandemic has boosted self-organization among tourists, they have become more aware of the pandemic and they are wary of protecting themselves when travelling, instead of avoiding travel altogether. Moreover, the pandemic has significantly affected the economy of tourism businesses. Due to lockdowns and restrictions, business managers increased product prices because of sharp rises in food prices, witnessed reduced demand and cutbacks in staff wages. Other tourism businesses were able to retain their workers and maintain staff salaries because they were profiting by raising prices of products and providing essential services to customers which they considered a blessing in disguise. The study also identified business management practices and risk management strategies used by the managers of tourism businesses during the pandemic. Businesses suddenly found themselves on the edge of chaos. As a result, managers had to self-organize and invest in new markets while creating unusual attractions as a lock-in effect to reward and retain existing customers and, perhaps, add new ones. The study also provided empirical evidence confirming the futility of the one-size-fits-all approach of deterministic linear models in crisis management. It is recommended that further Stellenbosch University https://scholar.sun.ac.za iv investigation be done into the socio-economic impact of the pandemic on other components of the versatile tourism industry in Nigeria and the rest of Africa. The research results contribute to a better understanding and management of crisis from the point of view of chaos theory, with particular emphasis on the tourism sector of Plateau State.

Browse

Recent Submissions