A framework for multi-risk assessment in a historical area of Lisbon

Historic areas have faced escalating risks due to population growth, urbanization, climate change, and increasing public awareness. Existing risk assessment methods often focus on individual hazards, necessitating a more integrated approach. This research introduces a comprehensive multi-risk model to assess the potential impacts of rainfall and earthquakes on Lisbon's historic city centre. The model considers key risk components – hazard, exposure, and vulnerability – providing a detailed evaluation. Pluvial flood hazards for different return periods were analysed using a proper hydrological model, and seismic hazards were estimated based on PGA values (0.035g–0.25g) with a 10 % exceedance probability over 50 years. Concerning the exposure, the paper integrates spatial distribution data acquired through satellite remote sensing and GIS tools, along with census data. Vulnerability assessments for ordinary unreinforced masonry buildings (URM) used the Risk-UE method and flood stage-damage curves. The results obtained through a multi-exposure and multi-vulnerability framework provide insight into the expected building losses: for a 475/500-year return period, the estimated losses are approximately 1150 M€ for earthquakes and 22 M€ for floods. The higher losses for earthquakes are attributed to structural damage, whereas flood losses are predominantly associated with indirect impacts and loss of contents. This study marks a novelty in the application of risk assessment methodologies in Portugal addressing multiple hazards and highlights the protection of the built environment to mitigate economic and human losses. The paper serves as a starting point for further assessments, offering an overview of the influence of multiple risks on urban settings.