On the morning of the first of November 1755, one of world’s deadliest and most powerful earthquakes struck Downtown Lisbon with a magnitude that ranged between 8.5 and 9.0. By the end of the week, the earthquake had killed 75,000 people. The earthquake coincided with the Catholic holy feast day of All Saints, and Portuguese worshippers streamed to Lisbon’s churches and cathedrals to celebrate, unaware that the old churches and cathedrals weren’t designed to withstand an earthquake of this magnitude. Many worshippers died as the roofs of their places of worship collapsed. Centuries later, has Downtown Lisbon changed enough to endure similar disasters in the future?

Four researchers from Portugal, Australia, and Germany, published a study on February 2018 to investigate how the City of Lisbon has changed over the years, dating back to not only the great earthquake, but the tsunami and fires that followed. Through Geographic Information System (GIS) mapping of the city, the study, which is titled “The changing city: risk and built heritage. The case of Downtown Lisbon,” identifies the exposure of the built heritage of Lisbon’s city center to natural hazards, including earthquakes, tsunamis, floods, and landslides.

This study is especially significant due to the recent conversation around resilient cities. The World Bank’s calculates that disasters costs an annual $520 billion and cause the impoverishment of 24 million people. The researchers ask whether these buildings would be able to withstand a similar event now or whether they have they been compromised by the changes that have occurred in and around them. This study investigates the vulnerability of the city’s historic structures and sites, which have withstood a number of disasters.

After the 1755 disasters, Lisbon decided to build a modern, commercial, disaster-resilient city, represented in Downtown Lisbon, which locals call Baixa Pombalina. Some of the country’s leading engineers and architects at the time worked on this project under the command of the Marquis of Pombal and the Crown’s Engineer Manuel da Maia. “Maia’s design included respect for certain attributes of the destroyed city, including retention of the principal road axis, the location and size of the main squares and use the same hierarchical street naming scheme,” the study reads.

Downtown Lisbon is located in a high seismic risk area, according to the sectorial diagnosis of “Risks and Civil Protection” included in the Regional Plan of Lisbon Metropolitan Area (link in Portuguese). This is due both to its proximity to active underwater structures bordering the Portuguese mainland, and to a fault zone in the lower Tagus Valley. The city center is also built on areas that have high seismic risk, both along the waterfront and over its ancient streams.

Downtown Lisbon was built over river flats and the remains of earlier settlements, in spite of its alleged fire- and earthquake-resistant design. The researchers observe that in many parts of the city, a timber platform and piles were used to provide a stable base for construction and some protection from liquefaction in a seismic event. Although most of the piles uncovered today appear to be undamaged, others that were uncovered were decayed, such as Bank of Portugal and Millenium Bank’s archaeological sites.

The study also discusses the city’s vulnerability to and resistance against fires, referring to several fires that caught in the city in the 20th Century. The most damaging – the 1988 Fire in the historic Chiado district (right next to Downtown Lisbon) – destroyed 18 commercial buildings and 40 businesses and left 300 people homeless and 2,000 more jobless.

In 1988, just when the city was rebuilding the downtown area, newly introduced street furniture and café structures often served to hinder fire-fighters’ response. Therefore, the researchers conclude that fire risk to Baixa Pombalina’s buildings will be determined by the vulnerability of their timber-framed construction, their use, contents, age, and the condition of their electrical wiring, as well as the capacity of their occupants to respond to a fire. The researchers shed light on the fact that many of the residents of Baixa Pombalina are now elderly and highly vulnerable, both physically and economically, and would find recovery from such disasters – regardless of how powerful – very difficult.

Given the aforementioned conditions, the researchers conclude that a disaster as deadly as the 1755 earthquake could cause irreversible abandonment of the district and an incalculable loss of heritage, represented in the cultural identity of Downtown Lisbon.

The researchers therefore recommend that authorities use GIS technology to map the heritage attributes of the city and overlay them with hazard susceptibility and infrastructure maps. “[This would enable] the development of more detailed analysis of risks to the urban fabric of Lisbon and the potential loss of its heritage values,” the study explains. The technology also provides the opportunity to link and share data across sites, enabling authorities to predict potential risks at neighbouring sites where relevant data is missing.”