Urban growth and spatial segregation increase disaster risk: Lessons learned from the 2023 disaster on the North Coast of São Paulo, Brazil

Abstract. Urban growth and the increase in urban poverty are important drivers of disaster risk. However, the influence of these processes on the dynamics of exposure and vulnerability remains uncertain. We hereby contribute to this discussion by presenting key lessons learned from the hazardous event that hit the North Coast of São Paulo (NCSP), Brazil, in February 2023. While the event was triggered by rainfall amounts of over 500 millimeters in a day, urban development processes also influenced the disaster impacts. In this paper, we quantify these influences through a data integration approach combining empirical evidence on the historical evolution of urban settlements with damage mapping. We also evaluate the factors driving urban growth and spatial segregation in the region. We found out that the disaster impacts were largely attributed to historical urban growth, as 46 % fewer buildings would have been damaged if the same event had happened around two decades earlier, i.e., in 2001. Also, precarious urban settlements were considerably more exposed and vulnerable to the event, as evidenced by the density of damaged buildings, i.e., 12 times higher than in non-precarious settlements. We also observed strong patterns of spatial segregation in the NCSP. For instance, precarious settlements are much more frequent at hazardous locations, including on and at shorter distances from steep slopes. While this paper presents an analysis at the local level, the challenges of urbanization and growing intra-urban inequalities are global. Thus, these results reinforce the importance of accounting for such urban processes in disaster risk reduction interventions, and the urgent need for research efforts that go beyond the hazard component, e.g., through an improvement of methods to simulate urban scenarios in the scope of disaster risk.