Chenyuan Wang

Traditional annual‐scale assessments obscure the dynamic recharge of debris‐flow provenances during concentrated rainy seasons. To address this, the spatiotemporal heterogeneity of monthly soil erosion during the rainy seasons (2022–2023) within debris flow‐prone gullies of the upstream Min River Basin was quantitatively evaluated using the RUSLE framework. During the rainy seasons, the mean monthly soil erosion modulus (SEM) reached 206.0 t ha ⁻¹ m ⁻¹ in 2022 and 153.3 t ha ⁻¹ m ⁻¹ in 2023. Spatially, severe erosion (> 12.5 t ha ⁻¹ m ⁻¹ ) was predominantly concentrated on high‐elevation ridges (e.g., Dengxi and Qipan gullies) and the hanging walls of seismogenic faults. Temporally, erosion exhibited extreme intraannual variability driven by precipitation shifts; notably, intense late‐season rainfall in September 2023 triggered catastrophic erosion surges in Zhangjiaping and Niujuan gullies, peaking at 259.8 and 262.1 t ha ⁻¹ m ⁻¹ , respectively. Additionally, the underlying physical mechanisms driving bank slope instability were elucidated. First, extreme disturbances dismantle the vegetative shield, causing a critical loss of root‐soil reinforcement against surface scouring. Second, the intrinsic fragility of the clay‐deficient soil matrix facilitates rapid infiltration and elevated pore water pressures, triggering structural mass slumping. Furthermore, SEM was positively correlated with sediment connectivity ( r = 0.32) and bulk density ( r = 0.38), and negatively correlated with soil depth ( r = −0.69) and available water capacity ( r = −0.69). These morpho‐edaphic factors form a self‐reinforcing positive feedback loop: enhanced sediment connectivity accelerates topsoil evacuation, exposing denser subsoils, restricting water capacity, and amplifying aggressive surface runoff. The research can provide a rigorous scientific foundation for targeted geohazard mitigation and watershed management in mountainous regions.

In order to assess the impact of the M_s7.0 Jiuzhaigou earthquake that occurred on 8 August 2017 on vegetation, the Carnegie-Ames-Stanford Approach (CASA) model was adopted to estimate the vegetation net primary productivity (NPP) of Jiuzhaigou Valley, one of the World Heritage Sites, in July, August and September from 2015 to 2019. Then the characteristics of the impact of different earthquake-induced geohazards on vegetation were discussed, and a vulnerability-resilience assessment system concerning the seismic intensity was proposed. The results show that the NPP_max and NPP_mean values in Jiuzhaigou Valley first decreased and then increased and were 151.5–261.9 gC/m² and 54.6–116.3 gC/m², respectively. The NPP value of more than 70% area was 90–150 gC/m² in July. In August, the NPP_mean values decreased, and the areas with lower values became larger; the NPP_mean values of most areas affected by geohazards were 60–150 gC/m². During the earthquake, the NPP_mean values of areas hit by geohazards sharply declined by 27.2% (landslide), 22.4% (debris flow) and 15.7% (collapse) compared with those in the same month in 2016. Vegetation in debris flow zones showed a stronger recovery, with a maximum NPP value increase of about 23.0% in September 2017. The vegetation gradually recovered after the earthquake, as indicated by the uptrend of the NPP values in the corresponding period in 2018 and 2019. In general, the reduction magnitude of NPP values decreased year by year in comparison to that in 2015 and 2016, and the decrease slowed down after the earthquake. The vulnerability and resilience index corresponding to the three seismic intensity ranges were 0.470–0.669 and 0.642–0.693, respectively, and those of Jiuzhaigou Valley were 0.473 and 0.671, respectively. The impact coefficient defined to represent the impact of the earthquake on NPP was 0.146–0.213. This paper provides a theoretical reference and guidance for the impact assessment of earthquakes on the ecosystem.