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    北京市山体滑坡空间格局与分异机制——以门头沟区“23·7”暴雨事件为例

    Spatial pattern and differentiation mechanism of landslides in Beijing: A case study of "23·7" heavy rain in Mentougou district

    • 摘要: 受台风“杜苏芮”影响, 2023年7月底至8月初, 京津冀地区发生强降雨过程并导致北京西南部门头沟区等地发生山体滑坡灾害。深入分析本次山体滑坡灾害的空间分异格局与影响机制, 对认识北京山区强降雨过程山体滑坡的成灾机制, 合理制订流域治理方案以降低区域水土流失风险具有重要意义。利用国产高分卫星影像及辅助资料, 精确提取滑坡信息, 并运用地统计方法对滑坡空间格局与分异机制进行系统分析。结果显示: 门头沟区此次洪灾过程中形成单体面积100 m2以上的滑坡5 680个, 总面积约5.85 km2, 滑坡空间分布呈现明显的局部聚集性特征。进一步分析发现, 滑坡严重度的异质性空间分布模式与地形坡度、植被覆盖度和土地覆盖类型等因素密切相关: 1)随着坡度增加, 滑坡密度与平均面积逐渐增大, 且单体滑坡面积的变异特征减小; 2)植被盖度增大则有效降低滑坡点密度与单体滑坡面积; 3)地表生产扰动水平在一定程度上影响滑坡严重程度, 裸地及农田等受生产活动扰动较大区域单体滑坡的规模更大, 自然植被区域林地覆盖地表的单体滑坡规模相较于灌木覆盖地表更小。研究表明: 虽然降雨是诱发研究区大规模山体滑坡的直接原因, 地形坡度、植被盖度和人为扰动等对滑坡灾害的空间分异特征存在重要影响。研究结果可为以北京为代表的华北地区防灾减灾工程建设和灾后恢复重建提供科学依据。

       

      Abstract:
      Background Affected by typhoon "Du Suri", from late July to early August 2023, heavy rainfall in the Beijing-Tianjin-Hebei region led to many landslide disasters in Mentougou district (MD), southwest of Beijing. At present, there has been no study on the disaster mechanism of landslides during heavy rainfall in North China, represented by Beijing. Therefore, exploring the spatial differentiation pattern and underlying influencing mechanisms of the landslide in MD holds utmost significance. Such an analysis offers a scientific foundation for the Beijing mountain area to effectively respond to landslide disasters triggered by heavy rainfall, thereby playing a crucial role in mitigating the risk of local soil erosion.
      Methods Utilizing pre-disaster and post-disaster satellite imagery along with auxiliary data, the landslide information was meticulously extracted. The general distribution characteristics of landslides caused by heavy rainfall were analyzed from a macro point of view. And then, the mechanism of the spatial differentiation of landslides in MD was explored further by statistical analysis and coefficient of variation using the digital elevation model (DEM), land cover and fraction vegetation coverage (FVC) data.
      Results It was found that a staggering 5 680 landslides (> 100 m2) occurred during the disaster, cumulatively affecting over 5.85 km2 of land in MD. Notably, the spatial distribution of these landslides demonstrated strong clustering patterns. In this disaster, many large landslides were distributed along the upper reaches of the Yongding River, and some of small landslides occurred from the upper reaches of the Ciwei River to the lower reaches of the Yongding River. Further investigation delved into the spatial differentiation mechanisms of these landslides. While the intense rainfall played a key role in triggering this widespread disaster, factors such as topographic slope, FVC, and land cover significantly influenced the severity of landslides. Three key findings emerged from our analysis: 1) As slope increased, both the density and average area of landslides rose, and the variability in landslide size decreased gradually. 2) Higher vegetation coverage translated to a decrease in both the density and average size of landslide. 3) The disturbance of land surface also influenced the severity of landslides. Areas subjected to greater anthropogenic alteration, such as bare land and farmland, tended to experience larger landslides compared to areas dominated by natural vegetation, particularly forests.
      Conclusions This study shows that topographic slope, vegetation coverage and human disturbance have important effects on the spatial differentiation characteristics of landslide hazards though rainfall is the direct cause of large-scale landslides in the study area. Landslide disasters caused by heavy rainfall are rare in Beijing. The spatial differentiation analysis of landslide caused by "23·7" flood in MD may improve the understanding of the mechanism of landslide in Beijing. Therefore, the results will provide a scientific basis for the construction of disaster prevention and reduction projects and post-disaster recovery and reconstruction in North China, represented by Beijing.

       

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