Environmental Flows Should Be Climate-Adapted and Can Reduce Downstream Impacts of River Flow Modification

Abstract Increasing demand and competition for resources requires integrated cross-sector planning and management. In northern Australia, demand for water resources to expand agricultural industries needs to be balanced with water requirements for ongoing function and support of freshwater and estuarine ecosystems. Using an integrated Model of Intermediate Complexity for Ecosystem assessment (MICE), we quantified impacts of flow modification from different hypothetical water resource development (WRD) scenarios (dams, water extraction and groundwater harvest) on downstream biota in the Roper River. Key flow-associated biota included prawns, barramundi, mud crabs, sawfish, mangrove and seagrass. We also assessed the impact of flows under future climate scenarios with and without WRD. Finally, we explored environmental flow scenarios to mitigate the impacts of WRD. Almost all modelled biota showed declines due to altered flows. Responses were non-linear and differed based on development type, with water extraction having a larger impact than dams. Sawfish and mangroves were particularly sensitive with average declines due to altered flows ranging from 1 to 53% and 9–31% respectively. Similarly, under a future dry climate declines were projected for almost all groups (except seagrass) and this was exacerbated with water resource development. Environmental mitigation practices such as end-of-system flow requirements and higher pump-initiation flow thresholds reduced the impact for most species, except sawfish. Our study highlights the importance of (1) identifying functional flow relationships and accounting for nonlinear outcomes resulting from flow alteration, (2) considering climate-resilience of mitigation strategies and (3) the importance of incorporating mitigation measures into WRD protocols to reduce impacts on estuarine biota, fostering integrated catchment management.