Browsing by Author "Grenfell, Suzanne"

Now showing 1 - 6 of 6
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    Climate variability: Human management response to environmental changes in Touws River valley and Makolokwe
    (University of the Western Cape, 2020) Llale, Semakaleng; Grenfell, Suzanne; Brooks, Shirley
    Climate has been changing significantly around the globe; hence climate variability is of great interest to researchers. The changes in climate have caused variances in rainfall and temperature, both elements of paramount importance in farming, whether commercial or communal farming. As these fluctuations in temperature and rainfall occur, they cause direct impacts on different livelihoods, fauna and flora. The aim of this thesis is to investigate the human management responses of farmers in two different contexts of communal farming (Makolokwe) and commercial farming (Touws River valley), with a focus investigation on the adaptation and coping strategies of the farmers, as well as spatial analysis of the vegetation and rainfall variability. Farmers were asked to discuss climate and adaptation based on the rainfall data available as well as far as they could remember the occurrence of changes. Rainfall data was available between 1988 and 2017 for Touws River, while the data utilised for Makolokwe was available between 1928 and 2016. The link between the local knowledge of the farmers and scientific knowledge is an important aspect of this research. The Normalised Difference Vegetation Index (NDVI) was used to analyse the vegetation changes on a temporal and spatial scale in the context of Makolokwe and Touws River valley respectively. The differing variations in climate variability and change experienced by the two farming communities are placed alongside an exploration of the adaptation and coping measures which are put in place by farmers as a response to the changes evident in climate, as it allows for better and thorough understanding of the occurring changes in the two communities. The study found that perceptions about climate variability vary in the two communities although there are some common factors. Farmers� perceptions about climate variability are drawn from their own observations at a local level as well as knowledge from the media regarding terms such as El Ni�o and drought. Farmers in both communities indicated that they experienced insufficient rain in the winter months which had an impact on the grazing areas and the management of the livestock. These months also threatened livelihoods, especially for farmers who depend on their livestock for their livelihood, in particular communal farmers. Perceptions of factors such as decreasing grazing and vegetation in their environments have led to the adoption of adaptation and coping strategies on the part of farmers. Commercial farmers have more choices in this regard than communal farmers, such as converting to game farming. Common coping strategies include: (1) farmers have had to subsidise and use alternative food sources for the livestock, (2) livestock numbers have been reduced in order to adapt to climate variability, with an impact on livelihoods (3) farmers have had to rely on their hope and faith that things will get better. Planning for climate variability is challenging for land managers. Knowledge and access to resources is therefore essential in ensuring that farmers are kept on track with the changing environment.
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    The impact of climate change and climate variability on coastal wetland ecosystem dynamics
    (University of the Western Cape, 2018) Fortune, Faeeza; Grenfell, Suzanne
    This thesis investigates the influence of climate change and climatic variability on wetland ecosystems (coastal and inland wetlands) on the Agulhas coastal plain. Firstly, this research examines coastal wetland ecosystem resilience to sea level rise by modelling sea level rise trajectories for the Dro? River wetland. The rate of sediment accretion was modelled relative to IPCC sea level rise estimates for multiple RCP scenarios. For each scenario, inundation by neap and spring tide and the 2-, 4- and 8-year recurrence interval water level was modelled over a period of 200 years. When tidal variation is considered, the rate of sediment accretion exceeds rising sea levels associated with climate change, resulting in no major changes in terms of inundation. When sea level rise scenarios were modelled in conjunction with the recurrence interval water levels, flooding of the coastal wetland was much greater than current levels for the 1 in 4 and 1 in 8 year events. The study suggests that for this wetland, variability of flows may be a key factor contributing to wetland resilience. Secondly, the thesis examines the variability of open wetland water surface areas and their relation to rainfall to determine wetland hydrological inputs for the Nuwejaars wetland system and respective wetlands. A remote sensing approach was adopted, Landsat 5 TM and 8 OLI multispectral imagery were used to detect changes of water surfaces for the period 1989 to 2017. Water surfaces were enhanced and extracted using the Modified Normalized Difference Water Index of Xu (2006). The coefficient of variation of wetland water surface area was determined. The variability ranges from low to high for respective wetlands. A correlation analysis of wetland water surfaces and local and catchment rainfall for the preceding 1, 3, 6, 9, 12 and 24 months was undertaken. The preceding month and associated inputs explains the annual variability of surface waters. The study suggests that, the variability of wetland water surface area are related to variations to water inputs and groundwater, as well as variations in water outputs such as evapotranspiration and an outlet channel.
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    Investigating the groundwater dependence and response to rainfall variability of vegetation in the Touws river and catchment using remote sensing
    (University of the Western Cape, 2019) Dlikilili, Sinethemba; Grenfell, Suzanne
    Changes in climate patterns have raised concerns for environmentalists globally and across southern Africa. The changes greatly affect the growth dynamics of vegetation to such an extent that climate elements such as rainfall have become the most important determinant of vegetation growth. In arid and semi-arid environments, vegetation relies on near-surface groundwater as the main source of water. Changes in the environment due to climate can be examined by using remotely sensed data. This approach offers an affordable and easy means of monitoring the impact of climate variability on vegetation growth. This study examined the response of vegetation to rainfall and temperature, and assessed the dependence thereof on groundwater in a climatically variable region of the semi-arid Karoo. The methodology used included sampling plant species in the riparian and non-riparian areas over two plant communities in seven vegetation plots. The Normalised Difference Vegetation Index (NDVI) derived from the Landsat OLI and TM was used to measure vegetation productivity. This was compared with rainfall totals derived from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) and the mean monthly temperature totals. A drought index, (Standardised Precipitation Index � SPI) was an additional analysis to investigate rainfall variability. Object-based Image Analysis (OBIA) and Maximum Likelihood supervised classification approaches together with indicators of groundwater discharge areas (Topographic Wetness Index � TWI, and profile curvature) were used to map vegetation and surface water that depend on groundwater.
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    Perceptions of wetland ecosystem services in a region of climatic variability
    (University of the Western Cape, 2018) Williams, Samantha; Grenfell, Suzanne; Carolissen, Mandy
    Wetlands provide various ecosystem services such as provisioning, regulating, supporting, and cultural services which may be directly or indirectly beneficial to humans. The manner in which such wetlands are managed is partly determined by human perceptions of their value. However, climatic variability and climate change put the continued provision of such ecosystems under stress. The result is that certain ecosystem services may be provided to differing extents during anomalously wet or dry years. There is thus uncertainty as to the values ascribed to wetlands by people during varying climatic phases. This thesis focuses on understanding how people perceive the functioning of wetlands within our current climate against a background of climatic variability and climate change. This study explores people�s perceptions regarding the functioning of wetlands and ecosystem services provided during dry and wet years, as an indication of how climatic variability and climate change impact peoples� perceptions. The data was collected in the wetlands of the Agulhas Plain in the Nuwejaars Catchment. Five wetlands classified and scored using the WETEcoServices tool. In addition, five semi-structured interviews and three participatory mapping exercises with landowners were also undertaken. The study reports on the landowners� awareness of wetland ecosystems, ecosystem services and climatic variability and climate change. Provisioning, supporting, and cultural ecosystem services are frequently used by landowners, which can be impacted by climatic variability and climate change. The WETEcoService benefits and landowners perceptions of ecosystem services varies, as the WETEcoService direct and indirect ecosystem services are either effective or ineffective in dry and wet years. In contrast to landowners perceptions emphasising the importance of ecosystem services directly beneficial to them. The study recommends that the ecosystem services landowners perceive as important is linked to their interest to guarantee their participation in catchment management. WET-EcoService benefits can inform landowners and managers about ecosystem services degradation and whether their conservation methods are either positively or negatively impacting wetlands.
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    Wetlands in drylands: Diverse perspectives for dynamic landscapes
    (Springer, 2022) Grenfell, Suzanne; Grenfell, Michael; Tooth, Stephen
    The United Nations Environment Programme (UNEP 1997) classifes global drylands according to an Aridity Index (AI), defned as the ratio between mean annual precipitation (MAP) and potential evapotranspiration (PET). Drylands are areas where AI is <0.65, collectively incorporating subhumid, semiarid, arid and hyperarid settings (UNEP 1997; see Fig. 1). Wetlands in drylands (hereafter WiDs) have distinctive hydrogeomorphological, biogeochemical, ecological, and social-ecological features, and as a result, they require carefully tailored research and management strategies.
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    Will a rising sea sink some estuarine wetland ecosystems?
    (Elsevier, 2016) Callaway, R.M.; Bertelli, C.M.; Mendzil, A.F.; Tew, I.; Grenfell, Suzanne; Grenfell, Michael
    Sea-level rise associatedwith climate change presents amajor challenge to plant diversity and ecosystemservice provision in coastal wetlands. In this study,we investigate the effect of sea-level rise on benthos, vegetation, and ecosystem diversity in a tidal wetland in westWales, the UK. Present relationships between plant communities and environmental variableswere investigated through 50 plots atwhich vegetation (species and coverage), hydrological (surface or groundwater depth, conductivity) and soil (matrix chroma, presence or absence ofmottles, organic content, particle size) data were collected. Benthic communities were sampled at intervals along a continuum from saline to freshwater. To ascertain future changes to the wetlands' hydrology, a GIS-based empirical model was developed. Using a LiDAR derived land surface, the relative effect of peat accumulation and rising sea levels were modelled over 200 years to determine how frequently portions of the wetland will be inundated by mean sea level, mean high water spring and mean high water neap conditions. The model takes into account changing extents of peat accumulation as hydrological conditions alter. Model results show that changes to the wetland hydrology will initially be slow. However, changes in frequency and extent of inundation reach a tipping point 125 to 175 years from2010 due to the extremely low slope of the wetland. From then onwards, large portions of the wetland become flooded at every flood tide and saltwater intrusion becomes more common. This will result in a reduction in marsh biodiversity with plant communities switching toward less diverse and occasionally monospecific communities that are more salt tolerant.