Browsing by Author "Gibson, Lesley"

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    Characterizing degradation gradients through land cover change analysis in rural Eastern Cape, South Africa
    (MDPI, 2017) Munch, Zahn; Okoye, Perpetua I.; Gibson, Lesley; Mantel, Sukhmani; Palmer, Anthony
    Land cover change analysis was performed for three catchments in the rural Eastern Cape, South Africa, for two time steps (2000 and 2014), to characterize landscape conversion trajectories for sustained landscape health. Land cover maps were derived: (1) from existing data (2000); and (2) through object-based image analysis (2014) of Landsat 8 imagery. Land cover change analysis was facilitated using land cover labels developed to identify landscape change trajectories. Land cover labels assigned to each intersection of the land cover maps at the two time steps provide a thematic representation of the spatial distribution of change. While land use patterns are characterized by high persistence (77%), the expansion of urban areas and agriculture has occurred predominantly at the expense of grassland. The persistence and intensification of natural or invaded wooded areas were identified as a degradation gradient within the landscape, which amounted to almost 10% of the study area. The challenge remains to determine significant signals in the landscape that are not artefacts of error in the underlying input data or scale of analysis. Systematic change analysis and accurate uncertainty reporting can potentially address these issues to produce authentic output for further modelling.
  • Thumbnail Image
    Item
    Fire risk reduction on the margins of an urbanizing world
    (Emerald, 2020-10) Rush, David; Bankoff, Greg; Cooper-Knock, Sarah-Jane; Gibson, Lesley; Hirst, Laura; Jordan, Steve; Spinardi, Graham; Twigg, John; Walls, Richard Shaun
    Purpose: Globally, over 95% of fire related deaths and injuries occur in low- and middle-income countries. Within informal settlements, the risk of fire resulting in injury or death is particularly high. This paper examines fire risks in informal settlements in New Delhi and Cape Town, and tented informal settlements in Lebanon. Design/methodology/approach: Our analysis draws on primary sources, secondary literature, statistical data and qualitative interviews. Findings: The distribution of fire risk across urban societies is a fundamentally political issue. Residential fire risk can be tackled by accessible, affordable, safety-compliant housing. That said, important interim measures can be taken to mitigate fire risk. Some of the risks requiring attention are similar across our case studies, driven by high population densities; flammable housing materials; unreliable or inaccessible access to safe power sources; and – in the case of Cape Town and New Delhi particularly – the inability of fire services to reach sites of fire. However, these common risks are embedded in distinct social, economic and political contexts that must be placed at the center of any intervention. Interventions must also be aware that the risk of fire is not spread evenly within informal settlements, intersecting as it does with factors like gender, age, health and disability. Originality/value: Informal settlement fires have been under-studied to date. The studies that do exist tend to operate within disciplinary silos. This paper represents an important interdisciplinary approach to fire within informal settlements, which grounds technical data, modeling and experiments in political, social and economic realities.
  • Thumbnail Image
    Item
    Future land cover change scenarios in South African grasslands - implications of altered biophysical drivers on land management
    (Elsevier, 2018) Gibson, Lesley; Meunch, Zahn; Palmer, Anthony; Mantel, Sukhmani
    Future land cover changes may result in adjustments to biophysical drivers impacting on net ecosystem carbon exchange (NEE), catchment water use through evapotranspiration (ET), and the surface energy balance through a change in albedo. The Land Change Modeller (Idrisi Terrset 18.08) and land cover for 2000 and 2014 are used to create a future scenario of land cover for two catchment with different land management systems in the Eastern Cape Province for the year 2030. In the S50E catchment, a dualistic farming system, the trend shows that grasslands represented 57% of the total catchment area in 2014 decreasing to 52% by 2030 with losses likely to favour a gain in woody plants and cultivated land. In T35B, a commercial system, persistence of grasslands is modelled with approximately 80% coverage in both years, representing a more stable system. Finally, for S50E, NEE and ET will increase under this land cover change scenario leading to increased carbon sequestration but less water availability and corresponding surface temperature increases. This implies that rehabilitation and land management initiatives should be targeted in catchments under a dualistic farming system, rather than those which are predominantly commercial systems.
  • Thumbnail Image
    Item
    Geohydrological conceptualization from a remotely sensed simplified water balance in the sandveld, South Africa
    (Institute of Electrical and Electronics Engineers, 2012) Munch, Zahn; Gibson, Lesley
    ENGLISH SUMMARY : The Sandveld (Western Cape, South Africa), located on the Cape West Coast, is characterized by low rainfall and minimal river flows, however despite this limitation, significant aquifer systems are found [1]. The groundwater in the region supports extensive agriculture and supplies towns with water for domestic use. The use of remote sensing can influence the way in which groundwater resources can be managed despite the fact that it is a subsurface resource and therefore cannot be directly measured by remote sensing techniques. The G30F catchment in the Northern Sandveld is reported to be experiencing water stress due to increasing abstraction for domestic water supply and agriculture, particularly potato crops. As suggested by Brunner et al [2], we propose the use of the simplified water balance determined from remote sensing data to estimate recharge and discharge zones within the catchment. Furthermore, we propose that this method is a useful aid in the geohydrological conceptualization of this particular water system. Of particular interest is the use of the recently released MOD16 evapotranspiration (ET) data product together with a precipitation data product, highlighting the ease with which studies of this nature can now be executed.
  • Thumbnail Image
    Item
    Measuring and modelling evapotranspiration in a South African grassland : comparison of two improved Penman-Monteith formulations
    (South African Water Research Commission, 2018) Gwate, Onalenna; Mantel, Sukhmani K.; Palmer, Anthony R.; Gibson, Lesley; Munch, Zahn
    Accurately measuring evapotranspiration (ET) is important in the context of global atmospheric changes and for use with climate models. Direct ET measurement is costly to apply widely and local calibration and validation of ET models developed elsewhere improves confidence in ET derived from such models. This study sought to compare the performance of the Penman-Monteith-Leuning (PML) and Penman-Monteith-Palmer (PMP) ET models, over mesic grasslands in two study sites in South Africa. The study used routine meteorological data from a scientific-grade automatic weather station (AWS) to apply the PML and PMP models. The PML model was calibrated at one site and validated in both sites. On the other hand, the PMP model does not require calibration and hence it was validated in both sites. The models were validated using ET derived from a large aperture scintillometer (LAS). The PML model performed well at both sites with root mean square error (RMSE) within 20% of the mean daily observed ET (R2 of 0.83 to 0.91). Routine meteorological data were able to reproduce fluxes calculated using micrometeorological techniques and this increased the confidence in the use of data from sparsely distributed AWSs to derive reasonable ET values. The PML model was better able to simulate observed ET compared to the PMP model, since the former models both transpiration and soil evaporation (ES), while the latter only models transpiration. Hence, the PMP model systematically underestimated ET in a context where the leaf area index (LAI) was < 2.5. Model predictions in the grasslands could be improved by incorporating the ES component in the PMP model while the PML model could be improved by careful choice of the number of days to be used in the determination of the fraction of ES.
  • Thumbnail Image
    Item
    Monitoring effects of land cover change on biophysical drivers in rangelands using albedo
    (MDPI, 2019) Munch, Zahn; Gibson, Lesley; Palmer, Anthony
    This paper explores the relationship between land cover change and albedo, recognized as a regulating ecosystems service. Trends and relationships between land cover change and surface albedo were quantified to characterise catchment water and carbon fluxes, through respectively evapotranspiration (ET) and net primary production (NPP). Moderate resolution imaging spectroradiometer (MODIS) and Landsat satellite data were used to describe trends at catchment and land cover change trajectory level. Peak season albedo was computed to reduce seasonal effects. Different trends were found depending on catchment land management practices, and satellite data used. Although not statistically significant, albedo, NPP, ET and normalised difference vegetation index (NDVI) were all correlated with rainfall. In both catchments, NPP, ET and NDVI showed a weak negative trend, while albedo showed a weak positive trend. Modelled land cover change was used to calculate future carbon storage and water use, with a decrease in catchment carbon storage and water use computed. Grassland, a dominant dormant land cover class, was targeted for land cover change by woody encroachment and afforestation, causing a decrease in albedo, while urbanisation and cultivation caused an increase in albedo. Land cover map error of fragmented transition classes and the mixed pixel effect, affected results, suggesting use of higher-resolution imagery for NPP and ET and albedo as a proxy for land cover.
  • Thumbnail Image
    Item
    Remote sensing evapotranspiration (SEBS) evaluation using water balance
    (Water Research Commission, 2011-06) Gibson, Lesley; Munch, Zahn; Carstens, Marilie; Conrad, Julian
    ENGLISH SUMMARY : This report follows on from WRC Report 1690/1/09 (Gibson et al., 2009) entitled "Remote sensing as a tool for resource assessment towards the determination of the legal compliance of surface and groundwater use" which showed that due to many uncertainties and limitations with both the input data and methodology, it was not possible to determine the actual water consumption of individual farms or compliance to legislation. In this project, the aim was to address the uncertainties and limitations in WRC Report 1690/1/09 and thereby determine the efficacy or inefficiency of the method to highlight water-stressed catchments.
  • Thumbnail Image
    Item
    Towards the development of a probabilistic approach to informal settlement fire spread using ignition modelling and spatial metrics
    (MDPI, 2020-11-15) Cicione, Antonio; Gibson, Lesley; Wade, Colleen; Spearpoint, Michael; Walls, Richard; Rush, David
    ENGLISH ABSTRACT: Large conflagrations of informal settlements occur regularly, leaving thousands of people homeless daily and taking tens of thousands of lives annually. Over the past few years, a large amount of data has been collected from a number of full-scale informal settlement fire experiments. This paper uses that data with a semi-probabilistic fire model previously proposed by the authors, to illustrate the potential applications of the fire spread method proposed. The current model is benchmarked against a 20-dwelling full-scale informal settlement fire experiment, and the effects of the (a) ignition criteria, (b) wind direction, and (c) wind speeds on the predicted fire spread rates are investigated through the use of a parametric study. Colour maps of the fire spread rates and patterns are then used to visually interpret the effects of different types of fire scenarios and fire breaks. Finally, the fire spread capability within B-RISK is used to derive a linear equation for the potential fire spread rate as a function of the settlement spatial metrics (e.g., density and distance to nearest neighbour). To further illustrate the potential application of this work, the fire spread rate equation is then applied across the whole of Cape Town, South Africa, to show the 10 informal settlement areas most at “risk” of large conflagrations.