Impacts of changing environments on seasonal propagation from precipitation to streamflow

Streamflow seasonality, characterized by its unequal intra-annual distribution, is predominantly shaped by precipitation dynamics in non-snowmelt-dominated regions. However, climate change and human activities can alter the hydrological cycle, weaken the consistency in precipitation-streamflow seasonality, and further modify streamflow seasonality. Despite its importance, the mechanisms modulating precipitation-streamflow seasonality consistency remain underexplored. This study employs time-varying copulas and partial correlation analysis to identify and quantify the evolving seasonality inconsistency between precipitation and streamflow under the influence of multiple anthropogenic and climatic factors. In the Yangtze River Basin (YRB), recent environmental changes, including climate warming, vegetation greening, and reservoir regulation, have increasingly influenced the hydrological cycle. In this study, a slight intensification of precipitation seasonality is observed in half of the YRB watersheds, whereas streamflow seasonality is moderated in 90 % of the watersheds. The climatic and human-induced changes consistently weaken the dependency between precipitation and streamflow across seasons. Comparing the dependency strength between the periods 2006-2015 and 1982-1991, a decline of 17 % was observed in spring, 1 % in summer, 42 % in autumn, and 75 % in winter. Partial correlation analysis highlights three key factors driving the observed decrease in summer streamflow and increase in winter streamflow, with reservoir regulation exerting the most pronounced influence in winter. This study sheds new light on investigating streamflow seasonality in a changing environment.