## 2 Materials and Methods
### Determination of the Probability of Landslide Occurrence in Cluj County  
The probability of landslide occurrence in Cluj County was calculated using a semi-quantitative model, to determine the spatial probability of landslide occurrence according to methodological norms regarding the drawing and the contents of natural risk maps concerning landslides, a model which has also been used in other similar studies in Romania. In the first stage, this model involved the creation of a database of all the factors that may cause and/or trigger landslides, taking into consideration the previous studies performed in Romania. Such factors include lithology (\(K_{a}\)), geomorphology (\(K_{b}\)), structural features (\(K_{c}\)), hydrological and hydrogeological features (\(K_{d}\)), hydrogeological features (\(K_{e}\)), seismic coefficient (\(K_{f}\)), the degree of forest coverage (\(K_{g}\)), and the level of human intervention in the territory (\(K_{h}\)). In order to compute the probability of landslide occurrence in Cluj County, GIS technology was used, as it allows for manipulation of the database and extraction of information needed for the assessment of these types of natural processes [45]. The geological structure and lithology condition regarding the emergence of landslides were considered [46; 47; 48], as they are among the most important factors causing landslides [49; 50]. In the studied territory, the analysis of the landslide distribution according to geological classes obtained through digitization of the Geological Map of Romania, 1960, highlighted that most landslides develop in geological classes dominated by marks and tuffs (28.5% of landslides mapped in the county), marly clays, sands and tuffs (22.5% of the landslides located in the hilly sector of the county), clays, sandstones with coal, marls, and marly schists and tuffs (14% of the landslides), etc. (Figure 2). Taking into account morphometric features such as slope and altitude, influence coefficients were provided according to the intervals defined by Government Decision no. 447/2003 [34]. The elevation was reclassified according to the landslide probability classes defined by the Government Decision no. 447/2003 using a digital terrain model (DEM) with a resolution of 10 m, downloaded from [[https://www.ancpi.ro](https://www.ancpi.ro)]([https://www.ancpi.ro](https://www.ancpi.ro)), accessed on 1 March 2023. The slope was derived from the DEM using ArcMap 10.7.1 software and reclassified according to the same methodological specifications. Therefore, the landforms characterized by low slope values (0-20) are affected by insignificant erosional processes. These are drained by valleys in an advanced stage of maturity and have a low probability of landslide occurrence, thus receiving a 0.1 coefficient. Currently, about 1% of active landslides are located in such areas (Figure 3). An average or high probability of landslide occurrence, characterized by coefficients between 0.3 and 0.5, is found in the hilly areas with moderate or steep slopes, fragmented by valleys which have reached an advanced stage of maturity, with 80% of the active landslides in the county being located in these areas. The other 19% of the landslides affect the hilly landforms characterized by slopes steeper than 150, where there is a very high probability of landslide occurrence (Figure 3). Rainfall is one of the most important factors in triggering landslides [51; 52]. Most studies researching the probability of landslide occurrence aimed to identify the threshold values needed for triggering new events but also for the reactivation of older and unstable landslides [43; 53]. Figure 2: Landslide probability based on lithology (\(K_{a}\) coefficient). The annual average amount of precipitation modelled for Cluj County represented the basis of analysis for the identification of landslide occurrence probability according to the hydrological and climatic coefficients [6].