Utilisation des techniques géospaiales pour l’évaluation des transformations spatiales dues aux pressions anthropiques dans le canton Afféma (Sud-Est ivoirien) - HAL Accéder directement au contenu
Article dans une revue Photo-Interprétation. European Journal of Applied Remote Sensing (PIEJARS) Année : 2017

The use of geospatial technologies for monitoring human-caused land-use changes in the Afféma's canton (South-East of Ivory Coast)

Utilisation des techniques géospaiales pour l’évaluation des transformations spatiales dues aux pressions anthropiques dans le canton Afféma (Sud-Est ivoirien)

Résumé

The introduction of coffee and cocoa in the south-east of Ivory Coast has induced during the 20th century a profound change in this region’s landscape. The results has been a massive development and expansion of cash crops at the sacrifice of natural vegetation formations. This situation has grown stronger during the last decades with the promotion of oil palm and rubber plantations. Thus, the diversification of cash crops promoted by the Ivorian government endangers the natural resources and the availability of agricultural lands for the growing population of the region. The lack of data (mapping and statistics) about land availabilities and the level of human pressure hinder the decision-making for better resource management. The main objective of this study focused on land use/land cover mapping is to conduct a diagnosis on the state of land use and to analyze the spatial changes induced by the progress and diversification of cash crops. The Affema’s canton is located in the south-east of Ivory Coast (latitudes 5 °24’56; 5°31’47 north and longitudes 2°50’03 and 2°54’04 west), precisely in the realm Sanwi which is the setting of this study. The Affema’s canton with about 10 villages has an estimated area of 589,13 km². The great part of the canton’s population, estimated at 30061 in 2014 is rural and involved in farming. This study has recourse to remote sensing and Geographic Information Systems (GIS) as tools of investigation, analysis and monitoring of the south-east’s area landscape. In the present study we have used mainly two types of data available on the study site: three Landsat images acquired in 1986, 200 and 2014 and a topographic map. Otherwise, for the purpose of mapping and analyzing the land use/land cover some themes were selected: forest; coffee/cocoa plantations; oil palm; rubber cultivation; field/fallow; bare soil and water bodies. It is important clarify that those themes may change from one year to another, as new crops are gradually introduced in the area. Land cover mapping has been achieved from a supervised classification of Landsat data, using Maximum Likelihood (ML) algorithm to label each pixel as the most probable classic, with reference to 5 land cover classes (1986), 6 classes (2000) and 7 classes (2014). Validation of results was obtained using a set of 35 samples identified on the year 2014 image, namely 5 samples per class. On the year 2000 image; 30 samples including 5 samples per class were gathered. In 1986, a set of 35 samples including 5 samples per class was also selected. These samples’ coordinates were stored in a GPS for a verification and a consolidation in the field. After classification, sample points were checked from the field survey for accuracy assessment. In this study, the classifications accuracy was assessed through a confusion matrix. Considering land cover maps in 1986, 2000 and 2014, total accuracies of classifications, assessed from Kappa coefficients, are respectively 87 %; 85 % and 82 %, indicating satifactory results. The evaluation of the rate of recession or evolution rate Tx between 1986 nd 2014 was derived using the following expression: Tx = [(SP2 – SP1) / SP1] x 100, with SP1 = surface area in 1986, SP2 = surface area in 2014. Results indicate a great amount of spatial changes, mainly due to introduction of new cash crops. The decline of forest lands is very significant. In spite of developement of oil palms and rubber plantations, landscape is still strongly dominated by coffee and cocoa plantations. The comparison of land use/land cover maps in 1986, 2000 and 2014 derived from satellite imagery indicates that there is a significant increase in the anthropogenic pressures on the agricultural land. The main results of increased human impact on landscape is the expansion of agricultural land, representing now nearly 90 % of the land and inducing a saturation effect. The forest cover remains only as relict patches. Finally, our results clearly show the effectiveness of geospatial technologies to conduct a diagnosis on the state of land use/ land cover and analyze the spatial changes induced by the development and diversification of cash crops. The quantification of land use/land cover changes of the Afféma’s canton is very useful for environmental management groups, policymakers and for public to better understand the problem of agricultural land saturation.
L’introduction de la culture du café et du cacao a entrainé au siècle dernier une modification profonde du paysage naturel du sud-est de la Côte d’Ivoire. Ceci s’est traduit par un développement et une extension remarquable des cultures de rentes au détriment des formations forestières. Cette situation s’est accentuée dans les dernières décennies avec la diversification des cultures de rentes, faisant peser de réels dangers sur l’avenir des terres agricoles de cette région. Cette étude se propose au moyen de la télédétection et des systèmes d’information géographique (SIG) d’évaluer, à l’échelle du terroir villageois, la pression anthropique et les transformations spatiales occasionnées par le développement des cultures de rentes, afin de pouvoir envisager une meilleure gestion des terres. Le canton Afféma, situé dans le sud-est de la Côte d’Ivoire, constitue notre cadre d’étude. Les résultats des traitements numériques des images-satellites de 1986, 2000 et 2014 révèlent que les terres dans le canton Afféma subissent une très forte pression humaine, qui conduit à une saturation progressive de l’espace potentiellement utilisable par l’agriculture. Les formations forestières ont presque toutes été remplacées par des cultures de rentes. Cette situation constitue une réelle menace pour la population qui augmente, et dont les revenus proviennent principalement de l’exploitation des terres.
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Dates et versions

hal-01630402, version 1 (07-11-2017)

Identifiants

  • HAL Id : hal-01630402 , version 1

Citer

Armand Kangah, Kouadio Eugène Konan, Sylla Daouda. Utilisation des techniques géospaiales pour l’évaluation des transformations spatiales dues aux pressions anthropiques dans le canton Afféma (Sud-Est ivoirien). Photo-Interprétation. European Journal of Applied Remote Sensing (PIEJARS), 2017, 51 (3), pp.12-21. ⟨hal-01630402⟩
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