Urbanisation of Floodplains Reduces Species Richness of Several Taxonomic Groups Worldwide

ABSTRACT Aim Global urbanisation is one of the main threats to biodiversity worldwide, with consequences on human health. Many large urban areas are situated close to river floodplains to satisfy human needs. While studies have quantified the consequences of urbanisation on floodplain biodiversity at a local scale, no quantification exists at a global scale. Location Worldwide. Time Period 2020–2023. Major Taxa Studied Floodplain's aquatic and terrestrial vertebrates, invertebrates and plants. Methods From the Global Biodiversity Information Facility, we compiled a database encompassing 51,357,439 and 33,606,794 species occurrences for animals and plants respectively. We filtered these occurrences step by step, first with a raster layer delineating global floodplains, then with the urban centre boundaries of cities accounting for more than 300,000 inhabitants and their associated catchment areas. We finally obtained a database featuring floodplain urban and regional communities for a total of 1062 cities. Using rarefaction, extrapolation and sample coverage methods to ensure comparability, our database ended up with 530,426 species occurrences in 535 cities. To quantify the impact of urbanisation on floodplain biodiversity, we compared the species richness of each urban floodplain to that of its associated catchment area for 13 taxonomic groups. Results For all studied groups we observed a decline of species richness in floodplain urban areas ranging between 18% and 33%. Bivalves were the most impacted by urbanisation followed by butterflies and birds. Malacostraca were the least impacted. Conclusions Initiatives to centralise biological data can clearly inform on the worldwide effects of urbanisation on floodplain species richness. However, most cities included in this study were located in the Global North, which provides a partial light on the erosion of biodiversity associated with urbanisation. Future research should prioritise data production or acquisition and studies from the fast‐urbanising Souths which host the majority of biodiversity hotspots.