Shi et al.  found that in 40 major basins worldwide, both climatic and direct human impact contribute to observed flow changes to varying degrees. Climate change or variability is the main contributor to changes in basin-scale trends for 75% of rivers, while direct human effects on streamflow dominate for 25%. However, this does not consider attribution of the climate drivers to anthropogenic forcing. Using time series of low, mean and high river flows from 7250 observatories around the world  and global hydrological models  driven by Earth System Model  simulations with and without anthropogenic forcing of climate change, Gudmundsson et al.  also found direct human influence to have a relatively small impact on global patterns of streamflow trends. Gudmundsson et al.  further identified anthropogenic climate change as a causal driver of the global pattern of recent trends in mean and extreme river flow . Overall, the sign of observed trends and simulations accounting for human influence on the climate system was found to be consistent for decreased mean flows in western and eastern North America, southern Europe, northeast South America and the Indian sub- continent, and increased flows in northern Europe. Similar conclusions were drawn for low and high flows, except for the Indian sub-continent. However, in some regions, the observed trend was opposite to that simulated with anthropogenic climate forcing. Thus, human water and land use alone did not explain the observed pattern of trends.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report