An assessment of the landslide risk (Rls) for the territory of Bulgaria by administrative districts has been made by combining the vulnerability (V) and landslide hazard (Hls) maps. Landslides are a significant part of geological hazards and are widespread throughout the country. In order to assess the landslide risk for the territory of Bulgaria, it is necessary to take into account not only all landslides for a given region, but also its vulnerability, and thus to assess the level of landslide risk for this region, Rls = f (V, Hls). Landslide risk is determined by a risk matrix, using selected indicators and weighting coefficient of vulnerability and landslide hazard. Assessing the vulnerability of a region subjected to geological hazards is a key component of risk assessment. These include the exposure of infrastructure, industrial facilities and production capacity, residential buildings, regional GDP per capita and potential for human disability (defined by population density in the district). The data used is combined to create a map showing the vulnerability of each administrative district. Indicators of population density, GDP, length of road and railway networks and number of residential buildings were used to assess the vulnerability. The landslide hazard in each administrative district is determined by the intensity of landslide processes in the district, depending on the level of their activity and the affected area. The normalized (distributed) hazard of landslides for an administrative region is given depending on the area of the given administrative region. Landslides are categorized as active, potential and stabilized. The results express the weighted average hazard. Landslide hazard is rated from 1 to 5, where 1 means no landslide hazard and 5 means that landslide hazard has a very high intensity (very high hazard). The high degree of landslide hazard in turn leads to possible economic losses, social and environmental consequences (landslide risk). The intensity (level) of landslide vulnerability, hazard and risk is assessed as very low, low, medium, high and very high, and is shown on the relevant maps.

The present study examines the change in landslide susceptibility under climate change conditions. The Landslide Susceptibility Index for the territory of Bulgaria was determined using the Mora and Vahrson method, based on the weighted assessment of various adverse conditions and destabilizing factors on slope stability. The input data include precipitation, soil moisture, seismicity, relief, and lithological factor. The simulations for the current and future climate in the present study were performed for a reference period (1975–2004), which is representative of the current climate, and a second period, relating to the climate of the near future (2021–2050). The RCP8.5 scenario is used. The climate change model applied in the present study shows a slight decrease in the areas threatened by landslides. This is probably due to the reduced soil moisture parameters.

As part of the Reimbursable Advisory Services on Accelerating Resilience to Disaster Risks, the World Bank worked with the Interior Ministry of Bulgaria to develop a proposal for the National Disaster Risk Profile of Bulgaria. The purpose of this document, which is the fourth technical annex to the proposal for the National Disaster Risk Profile, is to provide particular conclusions, information, and techniques that were utilised to evalu-ate the risk of landslides in Bulgaria. For the first time at the national level, landslide risk assessment procedures based on ISO/IEC 31010:2019 Risk assessment techniques are being developed and applied in Bulgaria. The five primary categories in which the results are presented are physical safety, economic security, social well-being, environmental security, and security of tangible assets and critical infrastructure. The uncertainty (confidence) parameter is utilised, and it is subdivided into the following three basic categories: low uncertainty, medium uncertainty, and high uncertainty. The produced results demonstrate consistent applicability to empirical data analysis and real-world situations.

In recent years, society become much more interested in nature disasters that cause damage. The consequences of these destructive processes of a meteorological, hydrological and geological nature sometimes remain for years until the affected areas are recultivated, restored and recovered. These natural processes work together, often following each other or triggering each other to create a massive system of destruction that causes a lot of damage and often leads to death and numerous casualties. Moreover, with the changes in the global climate of the Planet, leading to the more frequent manifestation of more destructive natural phenomena - cyclones, storms, huge amounts of precipitation - lead to intensify and manifest in larger scales and volumes geological phenomena such as landslides, mudflows, mud - stone torrents, rockfalls, collapses of different character of slopes, linear and planar erosion etc. This is extremely relevant for Bulgaria, the territory for which is no exception to the manifestation of catastrophic natural phenomena. The country is located in an active orogenic zone as part of the Alpo-Himalayan tectonic belt, characterised by a complex tectonic structure, variable and diverse geological formations and rapid topographical changes. The main focus in the study is to present an advanced, multi-faceted framework for natural disaster risk assessment, integrating biodiversity and archaeological sites. Moreover, the assessments of natural risks made so far do not include sufficient attention to biotopes and archaeological and historical sites. The presented methodology is applied to landslide hazards in a pre-selected area along the northern Bulgarian Black Sea coast. The main goal of this paper is to identify socio-environmental risks in the studied region, as well as to construct risk profiles and visually represent both qualitative and quantitative risk levels in the socio-ecological system and biodiversity.

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