Spatio-Temporal Population Distribution and Evacuation Modeling for Improving Tsunami Risk Assessment in the Lisbon Metropolitan Area

Abstract

Lisbon, Portugal, is subject to significant risk of tsunami, and was hit by a very destructive earthquake-triggered tsunami during daytime in 1755. The Regional Plan for Territorial Management for the Lisbon Metropolitan Area (PROT), under discussion, includes a tsunami hazard map, showing that significant urbanized areas may be at risk of inundation. In order to consider the time dependence of population exposure to tsunami threats, we map and analyze the spatio-temporal population distribution in the daily cycle in the Lisbon Metropolitan Area. High-resolution day- and nighttime population distribution maps are developed using ‘intelligent dasymetric mapping’, i.e. using areal interpolation to combine best-available census data and statistics with land use and land cover data. Mobility statistics are considered for mapping daytime distribution, and empirical parameters used for interpolation are obtained from a previous modeling effort of part of the study area. In combination with the tsunami hazard map, information on infrastructure, land use and terrain slope, the modeled population distribution is used to assess people’s evacuation times, applying a GIS-based evacuation modeling approach to the city of Lisbon. The detailed spatio-temporal population exposure assessment allows producing both day- and nighttime evacuation time maps, which provide valuable input for evacuation planning and management. Results show that a significant amount of population is potentially at risk, and its numbers increase dramatically from nighttime to daytime, especially in the zones of high susceptibility. Also, full evacuation can be problematic in the daytime period, even if initiated immediately after a major earthquake. The presented approach is considered to greatly improve risk mapping and assessment and can benefit all phases of the disaster management process.