Predicting river flow dynamics using stable isotopes for better adaptation to climate and land-use changes

Adapting to climate and land-use changes requires accurate prediction of river flow dynamics, particularly the seasonally varying water fraction with a rapid response to hydroclimate changes. By analysing stable isotopes in water molecules from precipitation and rivers, here we identified the young water fraction (<2–3 months) and introduced a dynamic water retention indicator to depict river flow dynamics. Examining 20,045 samples from 136 perennial rivers and 45 large catchments globally, we categorized dynamic water retention as high, moderate or low. Around 25% of rivers showed low dynamic water retention, indicating faster responses to hydroclimate events, whereas 50% exhibited high dynamic water retention, suggesting slower responses. Dynamic water retention and young water fraction correlated with changes in crop cover, forest cover, air temperature and precipitation, demonstrating temporal variations in three European rivers with decade-long isotope records. Isotope monitoring of rivers emerges as a cost-effective tool for understanding river flow dynamics and improving water resource management within ongoing hydroclimate and land-use changes. Using stable isotopes, this study introduces an indicator of dynamic water retention that shows river flow dynamics are influenced by land use and hydroclimate characteristics, helping categorize catchment responses and improving water resource management.