Land use changes associated with urbanization may increase ecological risk and subsequent geohazard risk. Africa is particularly vulnerable at preset as, since 2005, the highest rates of rapid urbanization-associated forest degradation have occurred there. On August 14, 2017, a compound geohazard in Freetown, Sierra Leone, caused thousands of fatalities and destroyed hundreds of houses. Land use change is considered the main factor contributing to geohazard initiation. Here, we use Freetown as a case study to quantitatively assess the magnitude of the increase in ecological risk associated with land use changes. To achieve the aim, satellite images are used in the case study area from 2007 to 2017, the data are integrated into a geographic information system. A series of indices are then used based on the processed images to describe land use and ecological risk, including dynamic index, trend and state index, and ecological risk index. The results show that Freetown experienced a rapid urbanization process, together with an unbalanced increase in urban land and complex conversion of bare and grass land, from 2007 to 2017. Significantly degenerated forest was converted into urban land (2.77%), bare land (6.47%), and grassland (10.27%), while the ecological risk level increased from low to high. The ecological risk in the affected area of geohazard is found higher than that of the surrounding mountainous area. It indicates that vegetation may reduce the risk of disaster. This result is helpful for the trade-off between urban development and ecological protection and rational urban planning. For disaster resilience and sustainable development of Freetown, and also other rapidly urbanizing cities in mountainous areas, ecological protection must be incorporated into development planning.

中文翻译：

---

城市化的生态风险共鸣及其对地质灾害的影响：以塞拉利昂弗里敦为例

与城市化相关的土地利用变化可能会增加生态风险和随后的地质灾害风险。自2005年以来，非洲特别容易受到影响，因为自2005年以来，与城市化有关的快速森林退化率最高。2017年8月14日，塞拉利昂弗里敦的复合地质灾害造成数千人死亡，并摧毁了数百所房屋。土地用途的变化被认为是引发地质灾害的主要因素。在这里，我们以弗里敦（Freetown）为例，定量评估与土地利用变化相关的生态风险增加的幅度。为了实现这一目标，在2007年至2017年的案例研究区域中使用了卫星图像，并将这些数据集成到地理信息系统中。然后根据处理后的图像使用一系列指标来描述土地利用和生态风险，包括动态指标，趋势和状态指标以及生态风险指标。结果显示，从2007年到2017年，弗里敦（Freetown）经历了快速的城市化进程，城市土地增加不平衡，光秃秃的草地和复杂的土地转换。大量退化的森林被转化为城市土地（2.77％），光秃秃的土地（6.47） ％）和草地（10.27％），而生态风险等级则从低到高增加。发现地质灾害影响区的生态风险高于周围山区。这表明植被可以减少灾害风险。这一结果有助于在城市发展与生态保护以及合理的城市规划之间进行权衡。