Regional modeling of the impacts of tidal flooding in the context of average sea level rise in low-lying areas of Brazil's semi-arid coast

Abstract. This study assessed the risks and impacts of rising average sea levels on Brazil's semi-arid coastline in a low-lying coastal area with limited response potential, using freely available data and based on the central hypothesis that, even in conservative scenarios, there will be risks with significant impacts. The methodology integrated DEM calibration, geodetic validation of tide gauge data, flood modeling, and overlay with real estate grids to quantify damage. The results showed relative stability of astronomical tides, with projected extremes of up to 2.975 and 3.454 m, respectively, for a 20 year return period. Meteorological tides showed low values (≈ 0.11 m), although with episodic variability. The modeling indicated that up to 14 % of the total area (about 730 km2) could be affected in extreme scenarios, with progressive flooding of solar salt pans and low-lying urban areas. Cities such as Areia Branca, Macau, and Porto do Mangue are at the highest risk, with a 60 %–80 % probability of flooded days in severe scenarios. Economic losses were estimated at approximately BRL 36 million in residences (≈ USD 6.7 million) and BRL 158 million in land (≈ USD 29 million), with Areia Branca being the most impacted municipality. Towns such as Barra, Cristóvão, and Baixa Grande also experienced significant risks and damage. The findings reinforce the usefulness of open data for regional risk analysis, even recognizing limitations in spatial resolution and vertical uncertainties. The methodology proved promising, replicable, and useful for supporting adaptive policies in regions with low institutional technical capacity.