Magbosi Land, Water and Environment Research Center (MLWERC), Sierra Leone Agricultural Research Institute (SLARI), PMB 1313, Mile 91, Northern Province, Sierra Leone.
Institute of Remote Sensing and Information Application, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, People's Republic of China.
Environ Monit Assess. 2016 Aug;188(8):470. doi: 10.1007/s10661-016-5469-y. Epub 2016 Jul 14.
Freetown, the capital of Sierra Leone has experienced vast land-cover changes over the past three decades. In Sierra Leone, however, availability of updated land-cover data is still a problem even for environmental managers. This study was therefore, conducted to provide up-to-date land-cover data for Freetown. Multi-temporal Landsat data at 1986, 2001, and 2015 were obtained, and a maximum likelihood supervised classification was employed. Eight land-cover classes or categories were recognized as follows: water, wetland, built-up, dense forest, sparse forest, grassland, barren, and mangrove. Land-cover changes were mapped via post-classification change detection. The persistence, gain, and loss of each land-cover class, and selected land conversions were also quantified. An overall classification accuracy of 87.3 % and a Kappa statistic of 0.85 were obtained for the 2015 map. From 1986 to 2015, water, built-up, grassland, and barren had net gains, whereas forests, wetlands, and mangrove had net loses. Conversion analyses among forests, grassland, and built-up show that built-up had targeted grassland and avoided forests. This study also revealed that, the overall land-cover change at 2001-2015 was higher (28.5 %) than that recorded at 1986-2001 (20.9 %). This is attributable to the population increase in Freetown and the high economic growth and infrastructural development recorded countrywide after the civil war. In view of the rapid land-cover change and its associated environmental impacts, this study recommends the enactment of policies that would strike a balance between urbanization and environmental sustainability in Freetown.
塞拉利昂首都弗里敦在过去三十年经历了巨大的土地覆盖变化。然而，即使是对环境管理者来说，塞拉利昂也仍然缺乏最新的土地覆盖数据。因此，本研究旨在为弗里敦提供最新的土地覆盖数据。本研究获取了 1986 年、2001 年和 2015 年多时期的 Landsat 数据，并采用最大似然监督分类法。共识别出 8 种土地覆盖类别：水、湿地、建成区、密林、疏林、草地、荒地和红树林。通过分类后变化检测绘制了土地覆盖变化图。还量化了每种土地覆盖类别的持久性、增益和损失，以及选定的土地转换。2015 年地图的总体分类精度为 87.3%，Kappa 统计值为 0.85。从 1986 年到 2015 年，水、建成区、草地和荒地的面积呈净增长，而森林、湿地和红树林的面积则呈净减少。森林、草地和建成区之间的转换分析表明，建成区以草地为目标，避免了森林。本研究还表明，2001-2015 年的土地覆盖总变化（28.5%）高于 1986-2001 年（20.9%）。这归因于弗里敦的人口增长以及内战结束后全国范围内经济的快速增长和基础设施的发展。鉴于土地覆盖的快速变化及其对环境的影响，本研究建议制定政策，在弗里敦的城市化和环境可持续性之间取得平衡。
