Emerging Patterns of Changes in Intra-Annual Variability of Streamflow

Abstract

Large-sample observational analyses of changes in intra-annual streamflow variability remain rare. This study presents the first large-scale analysis of spatial patterns in long-term trends of intra-annual streamflow variability from 1970 to 2022 across free-flowing and non-free-flowing rivers in diverse climate zones. Analyzing 12,311 streamflow stations, we found ∼23% of stations exhibit significant trends in variability (∼11% increasing, ∼12% decreasing). A spatial pattern emerges, that is, increasing variability dominates in tropical regions, driven largely by declining low flows, while decreasing variability prevails in cold regions, mainly due to rising low flows. In arid and semi-arid transition zones, changes in variability are strongly associated with reductions in streamflow. Non-free-flowing rivers exhibit a higher proportion of decreasing variability than free-flowing rivers. Further analysis of precipitation variability shows a consistency of variability between precipitation and streamflow only in tropical regions, indicating widespread non-precipitation-led flow regime changes.