Browsing by Subject "geography"

Now showing 1 - 4 of 4
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    Aeolian dust emission dynamics across spatial scales: landforms, controls and characteristics
    (2018) von Holdt, Johanna R C; Eckardt, Frank; Wiggs, Giles; Hipondoka, Martin
    Variable erodibility (surface characteristics) and erosivity factors (meteorological conditions) result in dust emission dynamics being complex in both space and time. Accounting for localscale surface variability is critical to our understanding of dust emitting processes. This study identifies mineral dust using remote sensing, establishes emission thresholds through field measurements and identifies particle chemistry for major dust sources in the Central Namib Desert. Examining over 2000 Landsat images over a period from 1972 to 2016, identified 40 days of visually detectable dust, originating from sub-km scale point sources. The observations suggest that dust sources can be identified at the landform scales which particularly include ephemeral river valleys and saline pan surfaces. These persist throughout the 25-year record; however, a gradual shift in source point clusters is noted through time, which can be tentatively attributed to anthropogenic modification of the hydrological systems. A PI-SWERL (Portable In-Situ Wind ERosion Lab) wind tunnel was used to measure the emission potential of the Landsat derived targets. The most emissive sources were paleostockpiles of alluvial silt deposits and associated degraded nebkhas within the Kuiseb River Delta. These had a geometric mean emission flux of 0.076 mg m-2 s -1. In comparison, the active channel had a geometric mean emission flux of 0.008 mg m-2 s -1, undisturbed desert pavement 0.007 mg m-2 s -1, pan surfaces 0.001 mg m-2 s -1 and wadis within the gravel plains 0.030 mg m-2 s -1. The emission thresholds were augmented with site-specific field measurements such gravel cover (%), moisture content (%), particle size (µm), elemental composition (%) and shear and compressive strength (kg cm-2). A Boosted Regression Tree (BRT) machine-learning algorithm identified the most important surface and sediment characteristics determining dust emission from the measured surfaces. The model explained 70.8% of the deviance in the measured dust flux with the top predictor variables and their relative importance (%) as follows: gravel cover, 16%; moisture content, 14%; kurtosis, 13%; very coarse silt, 13%; very fine sand, 11%; fine sand, 8%; compressive strength, 7%, calcium, 7% and magnesium, 6%. Such an analysis can be used to identify critical thresholds for dust emission and standardise testing protocols. Linking landforms with such emission measurements allow for the assessment of two existing dust emission schemes: the Preferential Dust Scheme (PDS; Bullard et al. 2011) and the Sediment Supply Map (SSM; Parajuli et al. 2017). Although these schemes represent a major advance in our representation of dust emission source areas and erodibility, this study shows that these schemes still need to be improved to accurately depict dust emission potential. For the PDS this would include producing a global rasterised output with quantified dust emission potential and for the SSM, a more accurate classification of the highly emissive geomorphic units. Landsat source point sediments were subjected to physical and geochemical analyses and compared to samples obtained from passive collectors such as the Big Spring Number Eight (BSNE) and active PI-SWERL exhaust emissions, using an auto-SEM (QEMSCAN). This provided individual particle mineralogy (>2 µm resolution) for a total of approximately 10000 to 60000 particles per sample which enabled a comparison of particle size, shape and mineralogy. The samples consist of a mixture of minerals reflecting the varied metamorphic geology and consists predominantly of feldspar, quartz, mica, other aluminosilicates such as the alteration products epidote and chlorite and low to medium grade metamorphics such as amphibole and pyroxene, iron oxihydroxides, titanium minerals, carbonates and clay minerals.
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    International Environmental Justice and the Climate Change Challenge
    (2012-12) Lawhon, Mary; Ziervogel, Gina;
    This course module is one section of a larger course called Geography, Development and Environment that runs as a first year course in the Department of Environmental and Geographical Science at the University of Cape Town. The course work provided here is one of 3 modules including 1) the global economic environment, 2) regional dynamics of development, and 3) the North-South debates on environmental problems. This module falls under the theme of North-South debates on environmental problems. The courses use theories of underdevelopment and climatic change to explain global and regional inequalities and environmental problems. Key concepts in the course are: trade, foreign aid, regional integration, and climatic change. The objectives of this section of the course are to begin understanding: 1. the concepts of environmental justice and climate change, 2. the relationship between environmental change and development, and 3. the international politics of global environmental change, This topic provides the scope for debate among students because of the contentious nature of the subject, and the lack of clear answers. Importantly this course focuses on presenting multiple explanations and diverse viewpoints and is intended to provide context, history and structure for students’ thinking. Students are not provided with solutions, but instead encouraged to develop their own explanations and responses to climate change and justice. This 4 week module, supported by powerpoint slides, uses climate change to explore key environmental and geographical issues including: justice, scale, international equality, global political processes, and environmental change. We begin by examining the foundation and principles of the environmental movement, distinguishing between different types of environmentalism and articulating early environmental conflicts between the North and South (presentations 1, 2, 4). We then develop ideas of environmental justice (presentation 3) and how it applies to climate change.
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    Straining: Young Men Working through Waithood in Freetown, Sierra Leone
    (2015) Finn, Brandon; Oldfield, Sophie
    Junge Männer in der prekären Lage andauernder Arbeitslosigkeit oder Unterbeschäftigung im Nachkriegs-Sierra-Leone werden in der öffentlichen und politischen Debatte als wirtschaftlich unbeweglich oder als gefährlich und fYr Gewalt empfänglich dargestellt. Im Gegensatz dazu charakterisieren die Autoren dieses Beitrags die Arbeits- und Lebensbedingungen junger Männer in Freetown als straining – angespannt. Sie untersuchen die Logik dieser Situation permanenter Anspannung, welche innovativen Ideen die jungen Männer entwickeln, welchen Anforderungen sie ausgesetzt sind und wie ihre Aktivitäten sich innerhalb der Stadt verteilen, insbesondere wenn sie mit Verbot und Kriminalisierung des informellen Handels konfrontiert sind. Die Autoren zeigen auf, dass die Anspannung immer wieder neu entsteht und fortdauert, weil (nicht obwohl) junge Männer marginalisiert sind und nur Yber eingeschränkte Handlungsautonomie verfYgen. In dieser Lage entwickeln sie provisorische Aktivitäten, um die Zeit des Wartens, in der sie sich befinden, auf dynamische Weise zu nutzen. In ihrem BemYhen, den eigenen Lebensunterhalt zu sichern und ihre Familien zu unterstYtzen, bewältigen sie gleichzeitig den Übergang von Jugendlichen zu Erwachsenen. Die Autoren plädieren fYr ein differenzierteres Verständnis fYr die arbeitenden jungen Männer in Freetown, aber auch allgemein fYr die große Zahl junger Menschen in afrikanischen Städten.
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    Vulnerability to environmental change
    (2014-08-22) Ziervogel, Gina
    The material is presented in the form of powerpoint presentations for 6 sections. Activities to accompany the slides are presented here. The slides form the basis of presenting the theory and linking it to key literature. Examples are provided in many places of how the theory is applied in case studies, often from work that the lecturer has been involved in and relevant to the southern African region. It is suggested that teachers who use this material in other contexts draw on local examples to support the theoretical discussions. Course objectives: 1. understand theoretical concepts of vulnerability 2. overview of what methods to use to assess vulnerability 3. understanding of the concept and application of adaptation to climate change. This 4 week module on vulnerability to environmental change is part of a third year course called Sustainability and the Environment (EGS 3021F) in the Department of Environmental and Geographical Science , University of Cape Town. The course introduces the concept of vulnerability and explores its origin, drawing on three different conceptual approaches namely Risk/hazard, Political economy/ecology and Ecological resilience. It then looks at different methods for undertaking vulnerability assessments. Building on the theory and method sections it focuses on why the concept of vulnerability is important in the field of environmental change with a focus on climate change. The international process of assessing the science is explored followed by material addressing adaptation to climate change and examples of vulnerability and adaptation in practice in South Africa.