Évaluation des modifications de l'occupation des sols dans l'Est-Kavango en Namibie selon une approche multi-dates par objet

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Edward MUHOKO
Carlos de WASSEIGE
Vera DE CAUWER

Résumé

Les modifications de l'occupation des sols représentent une problématique mondiale, mais leurs effets peuvent être particulièrement sévères dans les pays en développement comme la Namibie, où elles perturbent le fonctionnement des écosystèmes et, de ce fait, la soutenabilité du développement économique. Les conditions arides en Namibie, dues à la faible pluviométrie et aux taux élevés d'évapotranspiration, amplifiées par les feux de brousse qui sévissent chaque année, se traduisent par un paysage hétérogène caractérisé par un mélange d'arbres, d'arbustes et de plantes herbacées. De ce fait, les cartes d'occupation des sols sont souvent imprécises à l'échelle du pixel. Cependant, et malgré leur précision relativement élevée, l'analyse d'images par objets est encore loin d'être largement utilisée pour les forêts tropicales sèches de l'Afrique australe. Cette étude vise à évaluer les modifications de l'occupation des sols selon une approche multi-dates par l'objet, afin d'en déterminer l'ampleur et la dynamique dans ce paysage hétérogène de l'Est-Kavango, région de Namibie où le couvert végétal est parmi les plus denses. La segmentation multi-dates, les valeurs moyennes des courbes et la différenciation des images ont permis de détecter les  modifications de l'occupation des sols sur quatre périodes (1990, 2000, 2009 et 2016). Pour toutes les périodes, la modification la plus fréquente est la conversion de forêts en terres agricoles. En 1990, les forêts recouvraient 58 % des terres de l'étude pour 55 % en 2016, tandis que, sur la même période, la superficie des terres agricoles doublait, passant de 3 % en 1990 à 6 % en 2016. Les résultats obtenus par l'approche novatrice adoptée pour cette étude sont prometteurs à la lumière des méthodes traditionnelles, où la détection de modifications postérieures au classement peut être erronée. La méthode utilisée peut donc être recommandée pour le suivi à long terme des modifications de l'occupation et l'utilisation des sols dans les zones caractérisées par des conditions environnementales biophysiques similaires.


 


 

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Rubrique
ARTICLE SCIENTIFIQUE

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