Increasing Risk of Ecological Change to Major Rivers of the World With Global Warming

• Published in: Earth's future 2021-11, Vol.9 (11), p.n/a
• Main Authors: Thompson, J. R., Gosling, S. N., Zaherpour, J., Laizé, C. L. R.
• Format: Article
• Language: English
• Subjects: Aquatic ecosystems; Basins; Climate change; Climate models; Ecological risk assessment; Ecosystems; environmental flows; Environmental risk; Fragility; Global climate; Global climate models; global hydrology; Global warming; Habitats; Heterogeneity; high flows; Hydrologic models; Hydrologic studies; Hydrology; low flows; Permafrost; River basins; River ecology; River flow; River networks; Rivers; Runoff; Simulation; Spatial heterogeneity
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2021EF002048

The hydrological characteristics of a river, including the magnitude and timing of high and low flows, are important determinants of its ecological functioning. Climate change will alter these characteristics, triggering ecological changes in river ecosystems. This study assesses risks of ecological change in 321 major river basins across the globe due to global warming relative to pre‐industrial conditions of 1.0, 1.5, 2.0 and 3.0°C. Risks associated with climate‐driven changes to high and low flows, relative to baseline (1980–2010; 0.6°C warming), are investigated using simulations from nine global hydrological models forced with climate projections from five global climate models, resulting in an ensemble of 14,445 baseline‐scenario members for each warming scenario (9 × 5 × 321). At the global‐scale, the likelihood of high risks of significant ecological change in both high and low flows increase with global warming: across all basins there is a medium‐high risk of change in high (low) flows in 21.4% (22.4%) of ensemble members for 1.0°C warming, increasing to 61.5% (63.2%) for 3.0°C. Risks are particularly pronounced for low flows at 3.0°C for many rivers in South America, southern Africa, Australia, southern Europe and central and eastern USA. Results suggest that boreal regions are least likely to see significant ecological change due to modified river flows but this may be partly the result of the exclusion of processes such as permafrost dynamics from most global hydrological models. The study highlights the ecological fragility and spatial heterogeneity of the risks that unmitigated climate change poses to global river ecosystems. Plain Language Summary Ecological conditions within the world's rivers are strongly controlled by the amount, variability and timing of water flowing within them. Climate change will impact river flows with implications for riverine ecosystems. We assess the risks of these ecological changes across the globe. Simulated river flow for 321 major river basins are provided by nine global hydrological models. Their meteorological inputs for 1.0, 1.5, 2.0 and 3.0°C increases in global mean temperature are provided by five global climate models. Simulated river flows are compared with simulations of a recent historical period (1980–2010). Risks of ecological change for 57,780 comparisons of recent versus climate change river flows are assessed using an approach that quantifies changes in high and low flows. We demonstrate incr