Globally observed changes in the timing of water availability attributed to climate change

Streamflow, a key measure of water availability, follows a prominent seasonal cycle characterized by its amplitude and phase representing the range between high- and low-flow and their timing. This natural rhythm has profound implications for both ecosystems and human societies. However, evidence for whether anthropogenic warming has altered the timing of water availability remains limited to specific regions. Here, we synthesize a global large-sample hydrology dataset and use the centroid timing of mass of streamflow as a robust metric to quantify changes in the phase of seasonal cycle of streamflow. We find that approximately 20% of gauging stations show statistically significant timing shifts. By integrating multiple gridded runoff products derived from observation-based reconstruction, reanalysis and land surface models, we further identify a globally coherent yet contrasting change pattern. Importantly, this pattern is reproduced only by climate model simulations that include anthropogenic climate forcing, providing evidence for a detectable fingerprint on the timing of global water availability.