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Floodplain and riparian ecosystems have cooler, wetter microclimatic conditions, higher water availability and greater vegetation biomass than adjacent terrestrial zones. Given these conditions, we investigated whether floodplain ecosystems allow terrestrial bird species to extend into more arid regions than they otherwise would be expected to occupy. We evaluated associations between aridity and the occurrence of 130 species using bird survey data from 2998 sites along the two major river corridors in the Murray-Darling Basin, Australia. We compared the effects of aridity on species occurrence in non-floodplain and floodplain ecosystems to test whether floodplains moderate the effect of aridity. Aridity had a negative effect on the occurrence of 58 species (45%) in non-floodplain ecosystems, especially species dependent on forest and woodland habitats. Of these 58 species, the negative effects of aridity were moderated in floodplain ecosystems for 22 (38%) species: 12 showed no association with aridity in floodplain ecosystems and the adverse effects of aridity on species occurrence were less pronounced in floodplain ecosystems compared to non-floodplain ecosystems for ten species. Greater vegetation greenness indicated that floodplain vegetation was more productive than vegetation in non-floodplain ecosystems. Floodplain ecosystems allow many terrestrial species to occur in more arid regions than they otherwise would be expected to occupy. This may be due to higher vegetation productivity, cooler microclimates or connectivity of floodplain vegetation. Although floodplain and riparian ecosystems will become increasingly important for terrestrial species persistence as climate change increases drying in many parts of the world, many are also likely to be highly affected by reduced water availability.