Response mechanisms of fracture seepage at Longmen Grottoes under rainfall

In the context of climate change, rainfall-driven fracture seepage has become a key factor threatening the long-term stability of open-air stone heritage, and its response mechanisms urgently require further elucidation. Taking the Longmen Grottoes as a case study, this study developed a high-spatiotemporal-resolution method for dynamic seepage identification by integrating infrared thermographic monitoring, meteorological data, and ImageJ-Python image-processing algorithms. On this basis, a climate-seepage coupling model was established through multivariate regression analysis. The results show that seepage occurs approximately 48 hours after peak rainfall, exhibiting a nonlinear diffusion pattern that evolves from point initiation to band convergence and finally to surface expansion, along with pronounced diurnal oscillations. Among the climatic factors, precipitation (35%), air temperature (28%), and solar radiation (18%) were identified as the principal drivers. In particular, solar radiation exerts an inhibitory effect with a phase lag of approximately 3 hours: for every 100 W/m² increase in solar radiation, the seepage area decreases by 15%~20%. This delayed suppression reflects the regulatory effect of the thermal inertia of the rock mass on the seepage process. By contrast, humidity and wind speed exert relatively weak influences, although under certain conditions they may either enhance or inhibit seepage. This study reveals the complex hydro-rock coupling mechanism driven by the combined effects of rainfall, thermal processes, and evaporation cycles, and provides a theoretical basis as well as methodological support for understanding water-induced deterioration and advancing preventive conservation of open-air stone heritage in semi-humid regions.