<b>Permafrost thaw </b><b>threatens</b><b> infrastructure and sustainable development of mountain regions</b>

To assess the impact of permafrost thaw on infrastructure damage, we calculated five key indices to quantify the effects of gradual warming, including the thermal index (It), settlement index (Is), bearing capacity index (Ib), risk zoning index (Ir), and analytic hierarchy index (Ia). Unlike previous studies that relied primarily on the majority-voting method, we further incorporated the retrogressive thaw slump susceptibility (Irst) and applied principal component analysis to develop a new permafrost hazard index (IGW+AT), which can systematically reflect gradual permafrost warming and abrupt thaw. In addition, we quantified the exposure of four infrastructuretypes to permafrost degradation under the Shared Socioeconomic Pathways Scenarios (SSPs). Furthermore, we estimated the additional maintenance costs for infrastructure functionality using the equivalent lifespan replacement model, and quantified the relationship between permafrost hazard and additional costs. Moreover, we analyzed the spatial heterogeneity and unequal impacts of these additional costs at the prefecture-level city based on the projections of future population and GDP. Finally, we highlighted the importance of protection and adaptation strategies, and quantified their effectiveness in mitigating infrastructure damage, providing essential scientific support for the sustainable development of mountain regions.