Bjarne Fog

Desertification in reverse? Observations from northern Burkina Faso

Abstract The idea of degradation of arid and semi-arid lands, often termed desertification in its irreversible form, due to human impact and/or climatic change has been much debated since the mid-1970s. From the time of the United Nations Conference On Desertification in Nairobi, 1976, certain areas of northern Burkina Faso have been pointed out as examples of severe desertification. Several studies demonstrated that revitalization of a series of E–W oriented fossille dunes in the Oudalan province was ongoing. The present study includes an analysis of the trends of vegetation development in the region, covering the period 1955 to 1994, with emphasis on the fossile dunes. It is demonstrated that desertification and revitalization of dunes were phenomena associated with the period between the early 1970s and the mid-1980s, and that the decline in vegetation cover on the dunes seems to have been reversed in recent years. The analysis is based upon time series of aerial photos and satellite images, field studies of vegetation, interviews with local people and review of relevant literature. The findings are discussed with reference to the debate concerning desertification and land degradation, as well as to the current revisions of the ‘range management paradigm’. The observations indicate that the environmental history of the region is complex and cannot be boiled down to ‘human-induced irreversible degradation’. Rather they support the idea of semi-arid cultural landscapes undergoing constant change in response to both human impact and climatic trends and fluctuations.

Remote sensing techniques for flood monitoring in the Senegal River Valley

Abstract Accurate mapping of the aerial extent and duration of yearly flooding of the Senegal River may aid the assessment of the continued viability of traditional flood recession agriculture, as well as the monitoring of hazards to people, irrigated agriculture, buildings and infrastructure. At the same time geomorphologic complexity and expanding rice cultivation requiring dikes and channels make prediction of flooding with hydrological models difficult. Satellite imagery is an aid to mapping yearly flooding, and in this study several techniques based on different sensors (medium and low resolution optical sensors and a Synthetic Aperture Radar) will be compared and validated against ground-based surveys. AH the tested methods were highly accurate, as well as their operational potential when combined with hydrodynamic modelling. The presented results focus on the 1999 flood.

Explaining NDVI trends in northern Burkina Faso

Many studies have shown a ‘greening of the Sahel’ on the basis of analysis of time series of satellite images and this has shown to be, at least partly, explained by changes in rainfall. In northern Burkina Faso, an area stands out as anomalous in such analysis, since it is characterized by a distinct spatial pattern and strongly dominated by negative trends in Normalized Difference Vegetation Index (NDVI). The aim of the paper is to explain this distinct pattern. When studied over the period 2000–2012, using NDVI data from the MODIS sensor the spatial pattern of NDVI trends indicates that non-climatic factors are involved. By relating NDVI trends to landscape elements and land use change we demonstrate that NDVI trends in the north-western parts of the study area are mostly related to landscape elements, while this is not the case in the south-eastern parts, where rapidly changing land use, including. expansion of irrigation, plays a major role. It is inferred that a process of increased redistribution of fine soil material, water and vegetation from plateaus and slopes to valleys, possibly related to higher grazing pressure, may provide an explanation of the observed pattern of NDVI trends. Further work will focus on testing this hypothesis.

Environmental change in the Sahel: reconciling contrasting evidence and interpretations

The Sahel has been the object of intensive international research since the drought of the early 1970s. A considerable part of the research has focused on environmental change in general and land degradation, land cover change and climate change in particular. Rich and diverse insights from many different scientific disciplines about these three domains have been put forward. One intriguing feature is that an agreement on the overall trends of environmental change does not appear to emerge: questions such as whether the Sahel is greening, cropland is encroaching on rangelands, drought persists remain contested in the scientific literature, and arguments are supported by contrasting empirical evidence. The paper explores the generic reasons behind this situation in a systematic manner. We distinguish between divergences in interpretations emerging from (1) conceptualizations, definitions and choice of indicators, (2) biases, for example, related to selection of study sites, methodological choices, measurement accuracy, perceptions among interlocutors, and selection of temporal and spatial scales of analysis. The analysis of the root causes for different interpretations suggests that differences in findings could often be considered as complementary insights rather than mutually exclusive. This will have implications for the ways in which scientific results can be expected to support regional environmental policies and contribute to knowledge production.

Changes within Small-Scale Agriculture. A Case-Study from the Southwestern Tanzania

Abstract Danish Journal of Geography 96: 60–69, 1996. The objective of this paper is through a case study from the southern highlands of Tanzania, to illustrate how the agricultural system has changed within a period from the mid-1950s to the early 1990s in response to both endogenous and exogenous forces. The focus is primarily on the latest response at village level to the liberalization process within the agricultural sector in the early 1990s. New methods, by which remote sensing data from high resolution sensors are used as primary input, are analysed in relation to monitoring and to evaluate rapid land use changes.

Field Scale Spatial Analysis of pH on Sodium Soils in Northern Burkina Faso

Abstract Geografisk Tidsskrift, Danish Journal of Geography 97: 66–75, 1997. Microscale variations of soil properties may have a pronounced impact on crop yields in the low external input agriculture in the Sahel. Using classical and geostatistical methods, spatial patterns of soil pH at 0.0–0.10 m, 0.30–0.50 m and 0.70–0.90 m depth have been analysed and mapped based on two hundred and eighty-one samples collected at 10 m x 10 m grid nodes on a one hectare test plot on a clayey, sodium affected soil used for millet cultivation in northern Burkina Faso. The mean surface soil pH is 7.39 and semi-variance analysis shows that the nugget effect accounts for nearly 100% of the sample variance, and therefore surface pH exhibits no spatial dependency at the separating distance. The mean soil pH increases to 7.83 and 7.90 at 0.30–0.50 m and 0.70–0.90 m depth, respectively. However, the coefficient of variation also increases, and at 0.70–0.90 m the field has areas of both alkaline and acid soil. The range of infl...

The CHIPS System for Satellite Image Processing

Kjeld Rasmussen, Henrik Steen Andersen, Jens Grundtmann, Bjarne Fog and Lasse Moller-Jensen: The CHIPS System for Satellite Image Processing. Geografisk Tidsskrift, Danish Journal of Geography 94:xx-xx. Copenhagen, Dec. 1994. CHIPS, a software system for satellite image processing and analysis has been developed at The Institute of Geography, University of Copenhagen. The background, philosophy and objectives of this development effort will be briefly presented. In recent years emphasis has been put on the development of methodologies for remote sensing of environment and agriculture in Third World countries. This includes both land cover/use mapping using high resolution satellite images and applications of low resolution satellite data. This paper will give examples of research applications of CHIPS within different fields, and illustrate how the requirements, defined by this research, influence its contents and development. The presented examples include the use of SPOT, Landsat and ERS-1 SAR data for ...