Assessment of the impact of rainfall on landslide activity in the Polish Carpathians over a decadal period

Abstract

This study analyses the impact of precipitation on groundwater level fluctuations and the activity of six landslides in the Polish Flysch Carpathians, using monitoring data from the Landslide Protection System project, including inclinometer measurements, rainfall records, and groundwater levels in colluvial deposits. Geodetic surveys of reference points installed on the landslides were also used to assess their activity. Selected measurement intervals were examined to identify rainfall conditions triggering landslide movement. Cumulative displacement curves revealed nearly continuous movement, with velocities ranging from 0.3 to 3 mm/month. Displacement values causing inclinometer column shearing varied from 38 mm (Witanowice) to 232 mm (Ruszelczyce), depending on shear zone thickness and rock plasticity. Acceleration typically occurred during prolonged rainfall, especially when monthly totals exceeded 100 mm. However, defining a precise rainfall threshold and timing of acceleration was difficult due to complex geological conditions, irregular precipitation patterns, and limited measurement frequency. The findings highlight the sensitivity of landslide activity to hydrological changes and emphasize the need for frequent, integrated monitoring to better understand and predict slope instability in flysch terrains.