Spatiotemporal correlation of rainfall intensity and subsurface acoustic emission parameters for landslide initiation

Rainfall-induced landslides pose severe geohazards in monsoon-dominated mountain regions. This study presents a coupled rainfall–acoustic emission (AE) monitoring system deployed at a landslide-prone slope near Narendra Nagar, Uttarakhand, India (Lesser Himalaya). AE signals were recorded from active hollow aluminium waveguides installed through mapped shear zones, synchronized with sub-minute rainfall data from an Automatic Weather Station. Analysis of 4,884 one-minute windows over the 2025 monsoon season revealed: (i) a site-specific critical rainfall intensity threshold of 2 mm/min (r = 0.70, p < 0.001); (ii) a non-monotonic AE energy response with an energy minimum attributed to capillary suction strengthening under partial saturation, the first field-scale documentation of this phenomenon; (iii) an actionable early warning window of 12–35 minutes; (iv) an adaptive windowing algorithm showing intensity-dependent optimal accumulation windows (1 min at > 4 mm/min, 60 min at < 1 mm/min); and (v) a dual-criterion (rainfall + AE) warning system that reduces false alarms by a factor of three compared to rain-only thresholds. A site-specific intensity–duration threshold (I = 0.088D^0.36) was derived from 51 AE-confirmed rainfall events. These results demonstrate the feasibility of physics-based, multi-criterion AE-driven landslide early warning in complex Himalayan terrain.