When rainfall meets tides: flood hazards in an Amazonian Metropolis

Urban estuarine areas are exposed to flooding caused by heavy rain and tidal processes in cities lacking adequate infrastructure. Our aim of this paper was to analyze the relationship between precipitation intensity, tidal dynamics, and flooding occurrence in Belém (Pará, Brazil), located in Guajará Bay. Flood-related losses and damage have occurred throughout the city, especially in central consolidated and peripheral areas. The materials and methods included data collected from weather stations (1961–2020) of the National Institute of Meteorology and remote sensing data (1990–2023) from the Climate Hazards Group InfraRed Precipitation with Station dataset. Tide data (2006–2020) were obtained from the Brazilian Navy website, and damage information was collected from news reports, scientific articles, and official databases covering the period from 1987 to 2020. The locations mentioned in these reports were georeferenced and mapped. The results showed that in 1961 and 1990, the months with the highest precipitation were February and March, while during the period from 1991 to 2020, the rainiest months shifted to March and April. Extremely intense rainfall led to flooding-related damage in all city districts. A total of 51 news reports detailing the damage caused by flooding related to excessive rainfall and tides were identified, of which 24 occurred under extremely intense conditions. The highest tides were recorded in 2010, reaching 3.9m, and in 2014, 2015, and 2019, the tides reached 3.8 m at noon. In exposed and vulnerable areas, combined rainfall and high tides are the major causes of flooding, according to analysis of coincidences. The most common damages included loss of furniture and household appliances, interruptions to urban mobility, urban infrastructure damage, and the temporary isolation of residents. The linkages between rain and tides may contribute to risk management and alert purposes.