Mapping Urban Flood-Prone Areas’ Spatial Structure and Their Tendencies of Change: A Network Study for Brazil’s Porto Alegre Metropolitan Region

Abstract

Historically, the main cause of urban disasters in Brazil is flooding events, which are becoming more recurrent due to climate changes and intensive urbanization, causing extensive infrastructure, economic and life losses. The formation of Brazilian Metropolitan Areas goes back to the early twentieth century, with urban expansion following river basins, as regional transportation relied on inland navigation. The transition to road-based transport structured further urban sprawl from the mid-twentieth century onward, as road-circulation axes expanded across flood-prone areas. Mapping those hydrogeological risks is important to understand their effect on the existent road-circulation network structure cohesiveness. From the hydrogeological risk assessment data, this article evaluates potential changes imposed by extreme flood events on the road infrastructure at municipal and metropolitan scales. Space Syntax methods applied to an empirical case – the Porto Alegre Metropolitan Region – allow for comparative analyses between the urban network of current and flooding-event simulations and depict (a) the urban grids’ structural transformations under flooding, (b) the road elements at risk, and (c) the system’s spatial integrity and circulation disruptions. The resulting cartography can subside governance and urban planning strategies to cope with floodings at different territorial scales, addressing changes on local–regional circulation patterns, system breaking points and tendencies of urban land parcelling on vulnerable areas.