Spatial modelling of cumulative human pressure in the tropical coastscape of Zanzibar, Tanzania

Coastal landscapes and seascapes (‘coastscapes’) are under immense anthropogenic pressures emanating from multiple human activities. We applied spatial modelling to characterise the cumulative pressures in the coastscape of Zanzibar’s main island Unguja (hereafter Zanzibar), in the western Indian Ocean. We modified the European Union’s list of the human pressures in this context, conjointly covering Zanzibar’s marine and terrestrial environments. We applied a widely accepted algorithm for modelling cumulative human pressure. Spatial data were gathered from various sources and, where primary data were absent, model results were used as proxies. We used a hexagon lattice with a resolution of 0.5 km2 to map the anthropogenic pressures within the coastscape. Five typologies of coastscape were identified. A total of 283.55 km (68.86%) of the island’s coastscape is under moderate to high anthropogenic pressure, while the remaining 128.06 km (31.14%) is under low to moderate pressure. Cumulative human pressures are highest in the urbanised coastal areas, especially Zanzibar City, and in the growth zones. Principal components analysis was used to further explore the coexistence of separate human pressures and their contributions to the cumulative human pressure. Predominant pressures within the coastscape were litter, noise, the introduction of synthetic compounds, and inputs of organic matter. We recommend the use of these results for coastal-zone management in Zanzibar and for prioritisation of the management efforts.

沿海景观与海洋景观（coastscapes）正承受着源自多重人类活动的巨大人为压力。本研究针对西印度洋地区桑给巴尔主岛温古贾（以下简称桑给巴尔）的海岸景观，运用空间建模方法刻画其累积人为压力特征。研究对欧盟（European Union）制定的人为压力清单进行了适配调整，使其可同时覆盖桑给巴尔的海洋与陆地两类环境。本研究采用了一套被广泛认可的累积人为压力建模算法，空间数据来源于多类渠道，若缺乏一手实测数据，则以模型推演结果作为替代指标。我们采用分辨率为0.5平方千米的六边形格网，对该海岸景观内的人为压力进行空间制图。研究共识别出5类海岸景观类型。该岛总计283.55千米（占比68.86%）的海岸景观承受着中等至高强度的人为压力，剩余128.06千米（占比31.14%）则承受着低至中等强度的人为压力。累积人为压力在城市化沿海区域（尤以桑给巴尔市为甚）及发展增长带中达到最高水平。本研究采用主成分分析（Principal Components Analysis）进一步探究各类独立人为压力的共存模式及其对累积人为压力的贡献程度。该海岸景观中的主要人为压力包括垃圾污染、噪声干扰、合成化合物引入以及有机质输入。本研究建议将上述研究成果应用于桑给巴尔的沿海区域管理工作，并以此为依据优化管理资源的优先级配置。