Assessing the potential impact of freshwater overconsumption beyond regional carrying capacity on riverine fish species richness

Consuming freshwater beyond the regional carrying capacity—the maximum volume of water that can be sustainably used by human activities—poses a critical threat to aquatic biodiversity and ecosystem integrity. Therefore, quantifying the potential impacts of such overconsumption is essential for guiding responsible and sustainable water use and for assessing the environmental impacts of global value chains. In Life Cycle Assessment (LCA), these impacts have typically been assessed through Life Cycle Impact Assessment (LCIA) frameworks, which develop spatially explicit characterization factors to quantify the potential damage to freshwater ecosystems caused by human water use. However, existing approaches generally treat water use as an undifferentiated pressure, without distinguishing between sustainable consumption and overconsumption beyond regional carrying capacity. In this study, we quantified the regional carrying capacity of freshwater consumption as the difference between available freshwater resources and the environmental water requirements needed to sustain aquatic ecosystems across approximately 11,000 watersheds worldwide, based on WaterGAP model. We then identified freshwater overconsumption by human activities and applied a global model relating freshwater fish species richness to river discharge and other covariates (elevation, basin area, and climate zone) to derive two species–discharge relationships (SDRs), distinguishing watersheds experiencing overconsumption from others. These SDRs were subsequently used to develop characterization factors measuring the effects of human freshwater consumption on freshwater fish biodiversity. Our analysis revealed higher characterization factors in watersheds where human water consumption exceeded regional carrying capacity, indicating stronger biodiversity impacts under overconsumption conditions. These findings highlight the importance of explicitly accounting for overconsumption in LCIA water-impact assessment models. Incorporating this distinction can improve the accuracy of global characterization factors and support more responsible and targeted freshwater management strategies aligned with biodiversity conservation goals. The model integrates LCIA consensus methods from the UNEP Life Cycle Initiative to enhance the assessment and make the biodiversity impacts more consistent with the midpoint impact assessment method “AWARE”.