The pervasive fingerprint of anthropogenic climate change is apparent in river flow at a global scale, according to a new study. While anthropogenic climate change has had quantifiable and profound effects on various Earth systems, including the global water cycle, evidence for its role in the observed changes in river flow and hydrological extremes recorded worldwide remains uncertain. Lukas Gudmundsson and colleagues analyzed thousands of time series of low, mean and high river flows from 7,250 observatories worldwide from 1971 to 2010. According to Gudmundsson et al., the historical observations revealed recent, spatially complex global hydrological trends - while rivers in some regions are drying up and flowing less, others are growing wetter, with more water coursing between their banks. Using a climate change detection and attribution approach, the authors compared the observational data to Earth system model simulations of the terrestrial water cycle. According to the results, patterns in global river flow are only consistent with model predictions that consider the effects of radiative forcing from anthropogenic climate change. The simulated effects of water and land management alone are not enough to explain the recent patterns. The findings suggest that climate change is the causal driver influencing the magnitude of river flows globally. In a Perspective, Julia Hall and Rui Perdigão argue that, while Gudmundsson et al.'s attribution to climate change is logical and likely in terms of process understanding of climate dynamics, the evidence they provide is "circumstantial;" other processes not captured by the models could contribute to the observed trends. "To improve the explanatory power of such important studies and to generate more confidence in such attribution statements, we need to move beyond these first-order assessments that involve simple proof of consistency and inconsistency when investigating the effects of climate change," Hall and Perdigão write.
For reporters interested in trends, a February 2021 Science study reported that 53% of the world's river basins have undergone marked changes in biodiversity, largely due to human activity. https://science.sciencemag.org/cgi/doi/10.1126/science.abd3369
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Journal
Science