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    “23·7”极端暴雨门头沟区滑坡分布与主要影响因素

    Spatial distribution and the main controlling factors of landslides in Mentougou district during the extreme rainstorm “23.7”

    • 摘要: 2023年7月30日-8月1日,北京市门头沟全区遭遇罕见极端暴雨事件,长历时前期降雨叠加短时高强度降雨诱发区域群发性浅层滑坡。为厘清滑坡分布特征及主控因子,本研究基于高分辨率BJ-2遥感影像与无人机航测数据,结合目视解译出7011处浅层滑坡点,并集成坡度、坡向、NDVI、土地利用等9类环境因子,运用核密度分析和随机森林模型,系统探究滑坡空间特征。结果表明:滑坡呈多核心集聚、沿河谷带状分布,主要集中于永定河及其支流流域。基于随机森林分析了9个影响因子对滑坡分布的重要性,其中坡度(17.5%)、NDVI(17%)和坡向(14.9%)为滑坡分布的主要控制因子。滑坡高发于坡度40°–50°区间及东南向坡面,利用开源12.5m DEM进行区域滑坡坡度分析时会导致结果相差高达20°,建议在地形复杂山区分析浅层滑坡坡度等地形因子时,最好利用高精度地形数据,以保证坡度结果可信。植被对滑坡的影响具有坡度依赖性:即在低坡度区域,NDVI高值(>0.7)对应滑坡面积显著上升,而在高坡度区域则呈负相关关系。本研究初步分析了“23.7”门头沟全域的浅层滑坡分布规律,有望对今后区域山地灾害监测预警质量提升工程以及未来滑坡泥石流发生发展趋势提供理论支撑。

       

      Abstract: Background From July 30 to August 1, 2023, the Mentougou District of Beijing experienced an unprecedented extreme rainfall event, later classified as the “23.7 Catastrophic Basin Flood.” This event, driven by the remnants of Typhoon Doksuri and the West Pacific Subtropical High, brought cumulative rainfall exceeding 1,000 mm in some locations. Unlike typical flash floods in the region, the 23.7 event triggered widespread shallow landslides and soil-driven debris flows, highlighting a rare but increasingly significant hazard pattern in the semi-humid, semi-arid climate zone of North China. The event’s uniqueness lies in its compound triggering mechanism: a combination of prolonged antecedent rainfall and short-duration, high-intensity precipitation episodes. Methods This study integrates high-resolution BJ-2 satellite imagery and UAV photogrammetry to identify 7,011 shallow landslides across Mentougou. A total of nine environmental variables—including slope, aspect, NDVI, lithology, land use, and distances to roads, rivers, and faults—were analyzed using kernel density estimation and a Random Forest model. High-accuracy DEM data from UAV coverage (151.82 km²) was used to extract refined terrain metrics for 1,995 landslide samples. The Random Forest algorithm was employed to evaluate the relative importance of each variable in shaping landslide spatial patterns, while kernel density mapping provided insights into distributional clustering.Results 1) The rainfall event exhibited dual-peak characteristics with extreme intensities. Cumulative rainfall exceeded 1,000 mm over 66 hours, with hourly maxima surpassing 130 mm. These values exceeded the 100-year return period thresholds and met both key triggering conditions for shallow landslides: prolonged saturation and peak-hour intensities far above regional thresholds. 2) Landslides showed strong spatial clustering along river valleys, especially in areas near the Yongding River and its tributaries. High-density zones (up to 88 events per km²) were concentrated in towns like Zhaitang and Yanhecheng. Landslide density decreased with distance from river channels, indicating the significant role of valley morphology and river erosion in landslide initiation. 3) Random Forest analysis revealed that slope (17.5%), NDVI (17.0%), and aspect (14.9%) were the dominant factors controlling landslide distribution. Southeast-facing slopes and gradients between 40° and 50° were particularly prone to failure. Anthropogenic variables such as distance to roads (11.2%) and night light intensity (10.8%) also played substantial roles, suggesting a strong influence from human activity. 4) Slope, vegetation, and aspect interacted in controlling landslide behavior. On slopes less than 40°, high NDVI values (>0.7) were associated with larger landslide areas, likely due to higher soil water retention. On steeper slopes (40°-70°), NDVI had a stabilizing effect, with higher values linked to smaller landslide areas, reflecting enhanced root cohesion and surface protection. 5) Comparison of slope data from 12.5 m DEM and UAV-derived DEM revealed deviations of up to 20°, with coarser data significantly underestimating slope steepness. This highlights the critical need for high-resolution topographic data in landslide susceptibility mapping, especially in complex mountain terrains.Conclusions The 23.7 rainfall event demonstrated a compound hazard mechanism that triggered a rare, widespread outbreak of shallow landslides in northern China's mountainous terrain. The landslides exhibited clear spatial clustering, closely tied to topographic, hydrological, vegetative, and anthropogenic variables. Slope, vegetation cover, and aspect emerged as dominant controls, while road construction and urban development also exacerbated local susceptibility. The findings stress the critical importance of high-resolution elevation data in such analyses and provide a valuable foundation for improving early warning systems and hazard mitigation planning in similar environments under a changing climate.

       

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