Expert knowledge in enhancing quality of landslide inventory maps: A LiDAR-based study from Vinodol Valley, Croatia

Landslide inventory maps (LIMs) are essential tools for hazard assessment, risk mitigation, and land-use planning. Expert knowledge significantly impacts their quality, potentially enhancing completeness and overall accuracy of landslide data. Experienced geomorphologists are trained to identify subtle topographic signatures of landslides, which is particularly the case of old or relict landslides or of complex geological settings, where the interpreters are supposed to deal with many sources of ambiguities.

This study examines the impact of expert knowledge on the quality of two geomorphological landslide inventory maps at a 1:10,000 scale in a geologically complex pilot area (45 km²) in Vinodol Valley, Croatia. The inventories were prepared through visual analysis of two LiDAR-based Digital Terrain Models (DTMs) at a resolution of 1m acquired in 2012 and in 2022. They were compared in terms of completeness, geographical accuracy, and thematic accuracy. 

The first landslide inventory map (LIM_A) was prepared by a single young researcher in 2018 using the 2012 LiDAR DTM. The second (LIM_B) was prepared in 2024 using the 2022 LiDAR DTM by a team of three experts, including two geomorphologists with decadal experience in geomorphological mapping and the author of LIM_A. Comparisons focused on the total number of landslides, completeness, degree of spatial agreement between the two maps, and landslide attributes, such as landslide classification, and relative age.

Results show that LIM_A is incomplete compared to LIM_B, especially when considering large and very large landslides, and LIM_B includes more landslides, especially old and relict ones, which are mostly poorly visible on DTMs. We maintain that the incompleteness of LIM_A, particularly focused on large, relict and less distinct landslides, can be attributed partially to the limited experience of the interpreter at the time of the mapping, and partially to the missing of a discussion approach in a multidisciplinary team.

This research highlights the importance of a collaborative approach in enhancing the quality of landslide inventory maps. While individual expertise is valuable, a diverse team of experts ensures more comprehensive and accurate mapping. Continuous training is essential to improve the detection of both recent and, especially, very old or relict landslides and to refine mapping skills necessary for accurate mapping in challenging environments.