The aim of this study is to assess the impact of the North Atlantic Oscillation (NAO) on both the winter precipitation and the temporal occurrence of different landslide types in Portugal. The analysis is applied to five sample areas located just north of Lisbon, the capital of Portugal. These sites are particularly relevant because actual dates of most of the recent landslide events are known but also because the landslides occurred in a suburban area with growing urbanization pressure. Results show that the large inter-annual variability of winter precipitation observed in western Iberia, i.e. Portugal and parts of Spain, is largely modulated by the NAO mode. In particular, precipitation falling in Portugal between November and March presents a correlation coefficient of R=–0.66 with the NAO index. Precipitation distribution for the reference rain gauge in the study area reveals that the probability of a wet month to occur is much higher for low NAO index composites than for the corresponding high NAO index composite. It is shown that this control, exerted by NAO on the precipitation regime, is related to corresponding changes in the associated activity of North-Atlantic storm tracks that affect the western Iberia. Landslide activity in the study area is related to both intense, short duration precipitation events (1–15 days) and long-lasting rainfall episodes (1–3 months). The former events trigger shallow translational slides while the later episodes are usually associated with deeper and larger slope movements. This second group of landslides is shown to be statistically associated with the 3-month average of the NAO index.

Social Vulnerability Index (SoVI) was applied to Greater Lisbon (Portugal). Based on the concepts used for the SoVI assessments in the US, 46 variables representing social vulnerability of the 149 civil parishes of Greater Lisbon were chosen. Thirty-eight variables were selected after application of correlation tests. They were standardized, and a Principal Component Analysis and a Varimax rotation were applied to them. Seven factors were extracted using the Kaiser criterion, which explain 79.5% of the variance, and the SoVI scores were then mapped using a standard deviation classification. Twelve of the 149 civil parishes of Greater Lisbon have a very high social vulnerability and 24 of them have a high social vulnerability. The map of SoVI was then integrated with susceptibility maps of earthquakes, floods, flash floods, landslides, tsunami, and coastal erosion, thus delineating risk zones. Twenty-two civil parishes of Greater Lisbon have a very high risk; among them, 17 belong to Lisbon Municipality, four belong to Loures Municipality, and one belongs to Vila Franca de Xira Municipality. Finally, exposed population was considered and combined with risk zones map in order to assess the number of people being potentially exposed to risk and their location.info:eu-repo/semantics/publishedVersio