Empirical rainfall thresholds for Carpathian landslides in Poland

Abstract This study aims to identify rainfall conditions that may trigger landslides in the Polish Carpathians by developing regional rainfall thresholds based on Intensity–Duration (ID) and Rainfall–Duration (ED) relationships. The thresholds were established using extensive precipitation and landslide data from 1996 to 2020 and validated with independent datasets from 2021 to mid-2024. This represents the first comprehensive threshold assessment for the entire Polish Carpathian region based on long-term meteorological records and a large landslide inventory. The threshold equations were defined for rainfall intensity and total rainfall as functions of rainfall duration. The results indicate that most landslides were associated with intense and long-lasting rainfall events, particularly those representing the upper range of recorded precipitation episodes. Validation showed that the thresholds effectively describe the general rainfall conditions favourable for landslide occurrence, although their ability to distinguish triggering from non-triggering events remains moderate. The findings confirm that rainfall thresholds can provide a useful basis for regional landslide early warning and hazard assessment. At the same time, they demonstrate that precipitation alone is insufficient for reliable prediction. Future forecasting models should therefore incorporate additional environmental and geotechnical factors, such as soil properties, slope morphology, land use, and antecedent moisture conditions.