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<p>Extreme rainfall and flooding in May 2024 caused the most severe hydrological disaster ever recorded in Rio Grande do Sul, southern Brazil, exposing deep socio-environmental vulnerabilities. This study examines the spatial relationship between flood extent and changes in the structure and fragmentation of natural vegetation within the Guaíba Hydrographic Region, a multifunctional landscape integrating urban areas, agricultural systems, and sensitive ecosystems. We hypothesize that flooded areas exhibit higher levels of vegetation loss and fragmentation, whereas landscapes with greater pre-event continuity tend to experience lower relative loss. Using land use and land cover data for 2023 and 2024, combined with flood extent mapping and landscape metrics, we quantified post-event structural changes in vegetation. The multivariate structure of the landscape was synthesized using Principal Component Analysis, and spatial associations with flooding were assessed through local bivariate spatial autocorrelation. Results indicate a 25.2% reduction in natural vegetation cover, accompanied by an approximately 20% increase in the number of fragments and a loss of core-areas, indicating intensified fragmentation following the extreme event. The principal components captured three structural dimensions, size and morphospatial complexity, internal cohesion and connectivity, and spatial isolation, all of which declined between 2023 and 2024. Before the event, in 2023, the flooded areas were associated with larger and more cohesive fragments; after the event, these areas exhibited greater isolation and reduced connectivity. The findings partially support the hypothesis, indicating that fragmentation is not solely driven by flooding but emerges from the interaction between event intensity and pre-existing landscape fragility. The 2024 flood appears to have acted as a catalyst of pre-existing structural vulnerabilities, demonstrating that territorial resilience depends not only on vegetation extent but also on its spatial configuration and connectivity. These results highlight the need for planning strategies focused on ecological connectivity and watershed-scale management.</p>

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Extreme flooding and vegetation fragmentation: post-event changes in landscape structure in southern Brazil

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年7月22日

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  • Raquel Weiss,
  • Martiele Wilhelm,
  • Ana Luisa Maffini,
  • Ariel Felipe Geraldo Zaghetti,
  • Maicon Pinto de Moraes,
  • Bárbara Giaccom

摘要

Extreme rainfall and flooding in May 2024 caused the most severe hydrological disaster ever recorded in Rio Grande do Sul, southern Brazil, exposing deep socio-environmental vulnerabilities. This study examines the spatial relationship between flood extent and changes in the structure and fragmentation of natural vegetation within the Guaíba Hydrographic Region, a multifunctional landscape integrating urban areas, agricultural systems, and sensitive ecosystems. We hypothesize that flooded areas exhibit higher levels of vegetation loss and fragmentation, whereas landscapes with greater pre-event continuity tend to experience lower relative loss. Using land use and land cover data for 2023 and 2024, combined with flood extent mapping and landscape metrics, we quantified post-event structural changes in vegetation. The multivariate structure of the landscape was synthesized using Principal Component Analysis, and spatial associations with flooding were assessed through local bivariate spatial autocorrelation. Results indicate a 25.2% reduction in natural vegetation cover, accompanied by an approximately 20% increase in the number of fragments and a loss of core-areas, indicating intensified fragmentation following the extreme event. The principal components captured three structural dimensions, size and morphospatial complexity, internal cohesion and connectivity, and spatial isolation, all of which declined between 2023 and 2024. Before the event, in 2023, the flooded areas were associated with larger and more cohesive fragments; after the event, these areas exhibited greater isolation and reduced connectivity. The findings partially support the hypothesis, indicating that fragmentation is not solely driven by flooding but emerges from the interaction between event intensity and pre-existing landscape fragility. The 2024 flood appears to have acted as a catalyst of pre-existing structural vulnerabilities, demonstrating that territorial resilience depends not only on vegetation extent but also on its spatial configuration and connectivity. These results highlight the need for planning strategies focused on ecological connectivity and watershed-scale management.