Comparing erosion processes in vegetated and non‐vegetated landslide slopes using the physically based SIMWE model and UAV‐LiDAR

Abstract

Vegetation plays a crucial role in regulating surface hydrology and reducing soil erosion, especially in landslide‐prone areas where slope instability intensifies runoff processes. Understanding how vegetation influences erosion in such dynamic environments is essential for effective land management and hazard mitigation. This study investigates erosion behaviour in vegetated and non‐vegetated areas of the Kalisari Landslide, Central Java, Indonesia, using simulations with the physically based Simulated Water Erosion (SIMWE) model. The model was parameterized with high‐resolution LiDAR‐derived elevation data, field‐measured infiltration rates and laboratory‐determined soil properties. Simulations were conducted for two rainfall events: a short‐duration (i) high‐intensity rainfall (84 mm h ⁻¹ for 30 min) and (ii) a lower intensity event (38.2 mm h ⁻¹ for 65 min). Two infiltration scenarios were evaluated: a real‐case scenario based on field measurements (72 mm h ⁻¹ in vegetated areas and 30 mm h ⁻¹ in non‐vegetated areas) and a reversed‐infiltration experiment designed to isolate the influence of infiltration on erosion response. Under high‐intensity rainfall in the real‐case scenario, mean erosion rates were ~0.28 kg m ⁻²  s ⁻¹ in the non‐vegetated zone and 0.18 kg m ⁻²  s ⁻¹ in the vegetated zone. In the reversed‐infiltration experiment, mean erosion increased to 0.52 kg m ⁻²  s ⁻¹ in the vegetated zone and decreased to 0.09 kg m ⁻²  s ⁻¹ in the non‐vegetated zone. These shifts represent scenario‐dependent changes of roughly 70% reduction in the non‐vegetated area and nearly 200% increase in the vegetated area, highlighting the strong sensitivity of erosion dynamics to infiltration variability. Event‐based validation using video‐derived water depths showed that simulated maximum surface flow reproduced the observed order of magnitude and relative vegetation contrasts. Under the 84 mm h ⁻¹ event, simulated depths (~1 cm in vegetated and ~4 cm in non‐vegetated channels) closely matched observed values (1 and 4 cm), while the 38.2‐mm h ⁻¹ event showed consistent relative differences in flow magnitude between vegetation conditions. Although absolute erosion magnitudes are subject to steady‐state modelling assumptions and parameter uncertainty, the results demonstrate that vegetation‐controlled infiltration plays a dominant role in regulating runoff and erosion patterns in active landslide terrain. The study provides process‐based insight into erosion dynamics in unstable tropical slopes and supports vegetation‐based approaches for local erosion mitigation.