Landslide hazard assessment: summary review and new perspectives P. Aleotti · R. Chowdhury This paper discusses various aspects of landslide hazard and risk assessment. In recent years, interest in this topic has greatly increased, with many technical papers published on the subject. This article presents a summary review and classification of the main approaches developed worldwide. The first step is to distinguish between qualitative and quantitative methods. The first group is mainly based on expert site-specific experience, with susceptibility/hazard determined directly in the field or by combining different index maps. The second group approaches are more formally rigorous, including statistical analyses (bivariate or multivariate) and deterministic methods based on geo-engineering models. These analyses can be deterministic or probabilistic. Among the quantitative methods discussed is the Neural Networks approach, which has only recently been applied to engineering geology problems. Finally, several considerations regarding the concept of acceptable risk and risk management are presented. Landslides – significance and impact In recent years, landslide hazard and risk assessment has become a major topic of interest for geoscientists, engineering professionals, and local communities worldwide. The main elements of a risk assessment system are shown in Fig. 1. Most available literature is based on terminology introduced in the 1980s (Varnes and IAEG 1984) and minor variations proposed by other authors (Einstein 1988; Fell 1994). The reader is assumed to be familiar with terms such as susceptibility, hazard, vulnerability, and risk, and their use in slope instability and landslide contexts. For a discussion on mechanisms and uncertainties related to landslides as natural hazards, see for example Chowdhury (1980). The increasing international interest in landslides is due to two factors: first, an increasing awareness of their socio-economic significance, and second, the increased pressure of development and urbanization on the environment. As development increases on sloping urban areas, a higher incidence of slope instability and landslides is reported. A database of reported slope instability events extending back many decades has been developed for the Greater Wollongong urban area in Australia (Fig. 2). From this, the effect of increasing development and urbanization has been inferred by Flentje and Chowdhury (1999). The increase in landslide risk is often due to the increase in both hazards and elements at risk (Fig. 3). In 1981, Varnes estimated that from 1971 to 1974, nearly 600 people were killed annually worldwide due to slope failures. Approximately 90% of these deaths occurred in the Circum-Pacific Region. In 1979, the International Association of Engineering Geology Commission on Landslides estimated that 14% of lives lost in natural disasters could be attributed to landslides. Alexander (1Landslide hazard assessment: summary review and new perspectives P. Aleotti · R. Chowdhury This paper discusses various aspects of landslide hazard and risk assessment. In recent years, interest in this topic has greatly increased, with many technical papers published on the subject. This article presents a summary review and classification of the main approaches developed worldwide. The first step is to distinguish between qualitative and quantitative methods. The first group is mainly based on expert site-specific experience, with susceptibility/hazard determined directly in the field or by combining different index maps. The second group approaches are more formally rigorous, including statistical analyses (bivariate or multivariate) and deterministic methods based on geo-engineering models. These analyses can be deterministic or probabilistic. Among the quantitative methods discussed is the Neural Networks approach, which has only recently been applied to engineering geology problems. Finally, several considerations regarding the concept of acceptable risk and risk management are presented. Landslides – significance and impact In recent years, landslide hazard and risk assessment has become a major topic of interest for geoscientists, engineering professionals, and local communities worldwide. The main elements of a risk assessment system are shown in Fig. 1. Most available literature is based on terminology introduced in the 1980s (Varnes and IAEG 1984) and minor variations proposed by other authors (Einstein 1988; Fell 1994). The reader is assumed to be familiar with terms such as susceptibility, hazard, vulnerability, and risk, and their use in slope instability and landslide contexts. For a discussion on mechanisms and uncertainties related to landslides as natural hazards, see for example Chowdhury (1980). The increasing international interest in landslides is due to two factors: first, an increasing awareness of their socio-economic significance, and second, the increased pressure of development and urbanization on the environment. As development increases on sloping urban areas, a higher incidence of slope instability and landslides is reported. A database of reported slope instability events extending back many decades has been developed for the Greater Wollongong urban area in Australia (Fig. 2). From this, the effect of increasing development and urbanization has been inferred by Flentje and Chowdhury (1999). The increase in landslide risk is often due to the increase in both hazards and elements at risk (Fig. 3). In 1981, Varnes estimated that from 1971 to 1974, nearly 600 people were killed annually worldwide due to slope failures. Approximately 90% of these deaths occurred in the Circum-Pacific Region. In 1979, the International Association of Engineering Geology Commission on Landslides estimated that 14% of lives lost in natural disasters could be attributed to landslides. Alexander (1