Cornelis Vanderpost

The use of integrated remotely sensed and GIS data to determine causes of vegetation cover change in southern Botswana

Abstract The characteristics and dynamics of dry savanna vegetation cover are receiving considerable attention from the perspectives of both global change and range degradation studies. Problems include the establishment of major savanna determinants and the floristic response of vegetation cover to given stimuli. Basic work on determinants is required to assess the nature and causes of natural resource depletion, particularly in the Kalahari region. Use of image processing techniques involving the association of pixel values and field data have resulted in the development of a vegetation map indicating floristic content and structure. Results indicate that a clear distinction can be made between classes containing high proportions of taller woodland species and those that contain mainly woody weeds. Degraded areas with sparse vegetation cover and large areas of bare soil were also identified. The GIS technique of buffer analysis was applied to determine the extent to which herbivory (livestock) and the gathering of bush products by the local population were directly involved in the spatial distribution of savanna types. Results indicate that most of the degraded areas are within 2 km of villages and boreholes. Most of the woody weed areas fall within a 2–4-km zone around boreholes. Spatial association indicates that uncontrolled bush product harvesting and goat grazing are primarily responsible for village-centred degradation, while cattle grazing around numerous boreholes is a primary cause of woody weed development. These kinds of savanna adaptive responses are difficult to reverse in rural Botswana because of increasing population pressure and concomitant poverty.

Interactions between fire and flooding in a southern African floodplain system (Okavango Delta, Botswana)

A series of 98 satellite images was analysed to reconstruct the fire and flood history of a floodplain system in southern Africa (Okavango Delta, Botswana). The data was used to investigate interactions between fire and flooding, and to determine the relevance of rainfall and flood-events for fire occurrences on floodplains and on drylands. The aims of the study are (1) to analyse and compare the fire frequency on floodplains and on adjacent drylands, (2) to investigate the influence of rainfall and flooding on the fire occurrence and (3) to determine correlations between fire frequency and flood frequency. The analyses show higher fire frequencies on floodplains than on drylands because of higher biomass production and fuel loads. The fire occurrence on drylands shows a correlation with annual rainfall events, while the fire frequency on floodplains is in principle determined by the flood frequency. Between floodplain types, clear differences in the susceptibility to fire where shown by analysing flood frequency vs. fire frequency. Here, the highest potential to burn was found for floodplains that get flooded about every second year. By calculating mean fire return intervals, the potential to burn could be specified for the different floodplain types.

Evaluation of vegetative criteria for near-surface groundwater detection using multispectral mapping and GIS techniques in semi-arid Botswana

Abstract The critical need to consider all options in the search for groundwater in semi-arid areas has promoted work on the possible association of near-surface groundwater and vegetation characteristics using a combination of remote-sensing data and geographic information systems (GIS) techniques. Two vegetative criteria (dense woody cover and abundance of deep-rooting species) are identified as being indicative of near-surface groundwater, and their spatial distribution is tested against the location of aquifers in southeast Botswana. Vegetative criteria classes were combined in a GIS environment with the distribution of geomorphic units and bedrock geology to determine the degree of coincidence with assumed or known aquifers. Results indicate that the distribution of dense woody vegetation as mapped from Thematic Mapper imagery has some potential in identifying especially surficial but also bedrock near-surface groundwater sources in mostly naturally vegetated semi-arid areas. Dense woody cover classes tend to select aquifers in topographically higher areas while classes comprising some deep-rooting species tend to select low-lying aquifers such as those occurring in fossil valleys. Deep-rooting species, however, are less successful as a vegetative criterion. Although various technical refinements are suggested, this work shows that vegetative criteria mapping can however be used in conjunction with conventional geological/geophysical techniques to enhance the prospects for groundwater location in relatively undisturbed semi-arid areas.

Groundwater investigation in semi-arid developing countries, using simple GIS tools to facilitate interdisciplinary decision making under poorly mapped conditions: The Boteti area of the Kalahari region in Botswana

Locating additional long-term groundwater resources in semi-arid regions of developing countries with growing populations is an expensive undertaking. Simple geographic information system (GIS) techniques can be utilised to facilitate efficient application of expensive geophysical techniques and test-drilling by functioning as an interdisciplinary integration and decision-making tool, especially in data-poor and poorly mapped environments where more sophisticated GIS techniques are not applicable. The paper demonstrates this in the context of the search for groundwater alternatives to the dwindling river water supply in the Boteti area of the Kalahari region in Botswana.

Rural livelihood diversification: A household adaptive strategy against flood variability in the Okavango Delta, Botswana

ABSTRACT This paper assesses the role of livelihood diversification in household adaptation to flood variability in the Okavango Delta, and locates it within the global discourse on adaptation to climate variability and change in developing countries. The contribution of livelihood activities to household income, level of livelihood diversity and the relationship between livelihood diversification and adaptation to flood variability was determined. Data from a survey of 623 households in five villages, focus group discussions and key informant interviews confirmed livelihood diversification as an important strategy for household adaptation to flood variability in the Delta. However, the household income portfolio was dominated by public transfers, underscoring the weak socio-economic status of the households and the effects of multiple shocks over and above flood variability. The study concludes that livelihood diversification and other household adaptive strategies may be sufficient for current flood variations, but may be inadequate for dealing with global climate variability and change in future.

Protected areas in Ngamiland, Botswana: investigating options for conservation‐development through human footprint mapping

Parks and reserves, created to protect Africa’s unique mammal life increasingly share buffer zones needed for their ecological survival with expanding rural populations, resulting in more conflict. While concern about the encroachment of human activity (or ‘human sprawl’) into natural areas is worldwide, it takes on an extra dimension in eastern and southern Africa, where we find the last large‐scale migrating herds of large mammals. The paper uses the Ngamiland region of Botswana in which the Moremi Game Reserve is situated to discuss problems and options surrounding park buffer zones in a context of rapid national economic growth, high levels of demographic growth and increasing international tourism activity, using human footprint and human sprawl mapping as tools to assess population conservation interaction. The paper argues that it is useful to employ footprint mapping in African protected area buffer zones to reveal specific regional patterns and options in order to enhance the search for workable solutions.

The nature and possible causes of land cover change (1984 –1996) along a rainfall gradient in southeastern Botswana

Land cover change analysis was undertaken in semi-arid southeastern Botswana. The aim was to determine how remotely sensed data could be applied over time and under different rainfall regimes to help assess the relative significance of biophysical and human factors in causing land cover change in a rapidly evolving developing world context. To this purpose, land cover changes were studied along an east (hardveld)-west (sandveld) gradient of decreasing rainfall and decreasing population density. Three years of Thematic Mapper imagery from 1984, 1994 and 1996, covering the period from the 1980s drought to the 1990s ‘normal’ rainfall regime were analysed using supervised classification techniques. Land cover change analysis revealed that over a large part of the study area the dry and more biophysically vulnerable western sandveld showed greater vegetation recovery than the eastern hardveld with its more productive soils and higher rainfall. Underlying causes behind this apparent reversal of trends are inferred to be mainly socioeconomic in nature and particularly related to higher population density due to the rise of salaried urban occupation opportunities in the hardveld. This work concludes that, while biophysical causes of change are important, the human dimension is regarded as being more significant especially where human factors negate otherwise positive biophysical effects in an agrarian developing country.

Household Water Insecurity in Different Settlement Categories of Ngamiland, Botswana

The attainment of water security is a major challenge confronting Botswana, a semi-arid country. This chapter analyzes household water security challenges in different settlement categories (i.e. primary centers, tertiary centers and ungazetted villages) of Ngamiland, Botswana. Informed by the concepts of security, water security and human security, the study used a survey of 554 households and qualitative data, collected through key informant interviews, participant observation, focus group discussions and informal interviews. The results of the study established that households across all settlement categories of Ngamiland encounter water insecurity in terms of availability and quality. Gazetted settlements households go for prolonged periods without water supply services. Households in ungazetted settlements use water from unprotected sources. The chapter concludes that the majority of households in different settlement categories are water insecure and this has negative effects on human security. Botswana has to put in place a water policy which emphasises the attainment water security and human security. Strategies and programmes aimed at enhancing household water security in both gazetted and ungazetted settlements have to be underpinned by scientific research.

Seasonal Declines in Rangeland Quality in the Cultivated Hardveld of Botswana Using Landsat Thematic Mapper Imagery

Abstract The need to combat both seasonal and long‐term drought are endemic in semi‐arid countries such as Botswana. These problems entail inter alia locating browse and certain bush derived foodstuffs (veld products) year long to enable local people to sustain their livelihoods. Seasonal range condition data are also required to help minimise overstocking and degradation. Results from seasonal reflectance curve analysis from southeastern Botswana indicate that most vegetation types can be identified especially on longer Thematic Mapper (TM) wavebands. Spectral Separability Indexes (SSIs) confirmed that range feature separation varies as a function of waveband and that feature separation is more pronounced in the wet, than the dry‐season. Results show that range feature differentiation is best attained using a combination of the chlorophyll absorpance band (TM3) and two mid‐infrared bands (TM5 and TM7). In terms of total seasonal separability, wet‐season vegetation cover differentiation was found to be 1.7 times more effective than that derived from dry‐season data. Both wet and dry‐season data sets were classified separately using maximum likelihood techniques. Although wet‐season data were more accurately classified, satisfactory class coincidence was achieved across the two data sets. Results indicate dry‐season declines in high quality rangeland and increases in bush encroached areas especially in communal areas comprising scattered villages. An appraisal of the ability of rangeland to sustain the needs of the rural poor in semi‐arid areas needs realistically to be undertaken during the dry season. Even though this time is sub‐optimal in terms of range condition assessment, it corresponds to the winter months when the demand for fuelwood is at its peak and available forage is minimal. Optimal timing, high resolution imagery and knowledge of local conditions are required to develop an information base which can help inform policy and direct poverty alleviation strategies.