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Application de la geomatique au suivi de la dynamique environnementale en zones arides

Abstract : This dissertation is focused on a research on the arid environmental change monitoring and modelling with application of geoinformatics (e.g., remote sensing, GIS, GPS) and geostatistic techniques taking the region of Nouakchott in Mauritania, North Ningxia and North Shaanxi in northwest China for examples. The objectives of the study were to monitor the urban and littoral environmental changes in Nouakchott, rural environment evolution in the two critical areas in northwest China in the past decades, to model the human-environment relationships and to understand the causes of the changes observed. Multi-temporal SPOT HRV images (for Nouakchott), Landsat TM and ETM+ images, county-level socio-economic data and meteorological data (for the sites in Northwest China) were used for these tasks. The methods and procedures adopted in this work were image registration, atmospheric correction, tasseled cap transformation, indicator differencing, change mapping and multivariate regression modelling.
The principal results from northwest China show that: not “advancing desert” was observed, however, signs of serious land degradation, e.g., vegetation degradation and soil salinisation, have apparently taken place due to cultivation practices, land reclamation and grazing. Some of these changes can be traced back to land use policies. Farmland extension is a remarkable rural environmental change in these sites and is associated with the increase in agricultural output. Taking up a small percentage of the total change, the urban extension is related to about 90% of the GDP growth and driven directly by the urban population and their socio-economic activities. Some river courses have been narrowing, owing partly to climate variability but mainly to the overuse of water in agriculture.
In Nouakchott, the urban has been extending outwards at a rate of 5.3% (or 3.6km2/yr) in response to the population growth. The rapid expansion in a narrow belt between the desert trail and ocean is a heavy burden charged to an already overburdened infertile land. The risk of seawater inundation in the urban and suburb area has been graded into three zones by spatial analysis. As well as the urban area, the littoral environment has also significantly evolved due to the construction of the Port de l'Amitié in 1987, the north beach has accreted at a rate of 0.08km2/yr and will reach its maximum limit in 13.4 ± 0.5 yr (2014-2015). The littoral drift will thereupon largely fill into the pool and the harbour will gradually reach the end of service if no measure is taken. The south beach has been in erosion at a rate of 0.12km2/yr with a maximum retreat of 362m in the period 1989-2001 and a potential of 277m is estimated for the period 2001-2011 due to the modifications of the wave direction and actions of the alongshore currents at a velocity of around 0.52-0.66m/s.
In brief, environmental change is deeply associated with human activities. Only having understood well such relationships and predicted the evolution tendency, can we make policies for better land use and environmental management.
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Submitted on : Friday, November 25, 2005 - 12:23:43 PM
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  • HAL Id : tel-00011113, version 1

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Weicheng Wu. Application de la geomatique au suivi de la dynamique environnementale en zones arides. Sciences de l'Homme et Société. Université Panthéon-Sorbonne - Paris I, 2003. Français. ⟨tel-00011113⟩

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