This study develops a dynamic risk modeling approach incorporating stock-and-flow structures to comprehensively evaluate the investment risks of highway PPP projects in Western China, aiming to promote sustainable infrastructure development. Through establishing a risk accumulation model with scenario simulation and sensitivity analysis, this study systematically examines the risk factors and their propagation pathways in Western China’s highway PPP projects. The research demonstrates the dynamic complexity of project risks, particularly highlighting the prominence of operation, maintenance, and government risks. Sensitivity analysis identifies five critical risk factors: financial support adequacy, public health contingencies, legal/regulatory robustness, inflation volatility, and project uniqueness. The study proposes targeted risk management strategies emphasizing the establishment of early-warning systems and emergency response plans for critical risks. Methodologically, this research advances infrastructure risk assessment by adapting stock-and-flow modeling conventions for threshold-driven risk screening, particularly suited to underdeveloped regions like Western China. The developed rapid risk determination tool provides practical decision support for stakeholders in similar socio-economic contexts.

Located on the northern side of the China–Pakistan Highway in the Pamir Plateau, Laqi Gully represents a typical rainfall–meltwater coupled debris flow gully. During 2020–2024, seven debris flow events occurred in this area, four of which disrupted traffic and posed significant threats to the China–Pakistan Economic Corridor (CPEC). The hazard assessment of debris flows constitutes a crucial component in disaster prevention and mitigation. However, current research presents two critical limitations: traditional models primarily focus on single precipitation-driven debris flows, while low-resolution digital elevation models (DEMs) inadequately characterize the topographic features of alpine narrow valleys. Addressing these issues, this study employed GF-7 satellite stereo image pairs to construct a 1 m resolution DEM and systematically simulated debris flow propagation processes under 10–100-year recurrence intervals using a coupled rainfall–meltwater model. The results show the following: (1) The mudslide develops rapidly in the gully section, and the flow velocity decays when it reaches the highway. (2) At highway cross-sections, maximum velocities corresponding to 10-, 20-, 50-, and 100-year recurrence intervals measure 2.57 m/s, 2.75 m/s, 3.02 m/s, and 3.36 m/s, respectively, with maximum flow depths of 1.56 m, 1.78 m, 2.06 m, and 2.52 m. (3) Based on the hazard classification model of mudslide intensity and return period, the high-, medium-, and low-hazard sections along the highway were 58.65 m, 27.36 m, and 24.1 m, respectively. This research establishes a novel hazard assessment methodology for rainfall–meltwater coupled debris flows in narrow valleys, providing technical support for debris flow mitigation along the CPEC. The outcomes demonstrate significant practical value for advancing infrastructure sustainability under the United Nations Sustainable Development Goals (SDGs).