The study, published in Nature Communications, examined changes in "blue water" (streamflow) and "green water" (soil moisture) between 1901 and 2019 and separated the relative impacts of direct human forcing and climate-related forcing on them. The study uses streamflow and soil moisture data produced by global hydrological models, based on which researchers analyzed the occurrence of anomalously dry and wet conditions relative to a baseline state that represents preindustrial-like stable conditions.
According to the study, the occurrence of anomalously dry and wet conditions has approximately doubled relative to the baseline conditions for both blue and green water. In many tropical and subtropical regions, increasing dryness is the dominant type of change, whereas anomalously wet conditions have become more frequent, especially in the northern boreal zone. Globally, these changes—and the transgression of the freshwater change planetary boundary—have been driven most strongly by climatic factors. Nevertheless, direct human forcing, such as water and land use, has had a significant effect, particularly on the global increase in anomalously dry conditions.
"The rate of change in the freshwater cycle has accelerated in recent decades, and scientific assessments and projections of future climate change indicate that this rate is likely to accelerate even more," says Postdoctoral Researcher Vili Virkki from the University of Eastern Finland, who led the study.
