Integrating Intensity–Duration and Antecedent Rainfall Thresholds for Shallow Landslide Prediction in the Eastern Himalaya, India

• Rainfall-induced shallow landslides pose a persistent hazard in the Eastern Himalaya, particularly along the strategically important Balipara–Charduar–Tawang (BCT) corridor in western Arunachal Pradesh, India. This study develops a region-specific rainfall threshold framework by integrating long-term rainfall trend analysis with empirical landslide-triggering thresholds to enhance early warning capabilities in this data-scarce, high-relief terrain. Daily gridded rainfall data from the India Meteorological Department (2000–2020) and an inventory of 236 landslide events recorded between 2008 and 2015 were analyzed. Trend analysis reveals a statistically significant decline in annual rainfall (–81.05 mm yr⁻¹), accompanied by pronounced inter-annual variability and persistent monsoonal dominance. Empirical analysis indicates that short-term antecedent rainfall plays a critical role in slope failure initiation, with 3-day and 5-day cumulative rainfall showing the strongest correlation with landslide occurrence (R² = 0.508 and 0.480, respectively). Corresponding 80th percentile thresholds of ≥89.24 mm (3-day) and ≥118.80 mm (5-day) are proposed as practical triggering criteria. In addition, an intensity–duration (I–D) threshold derived from 95 rainfall-induced landslides follows a negative power-law relationship (I = 17.26·D⁻⁰·¹⁰), capturing the influence of short-duration, high-intensity rainfall events. The combined use of antecedent rainfall and I–D thresholds effectively represents both progressive soil saturation and rapid-onset rainfall triggers. This integrated threshold framework provides a robust and scalable basis for landslide early warning system development along the BCT corridor and offers broader applicability to similar monsoon-dominated Himalayan regions.