Method for identifying non-stationary hydrological drought in regions with intense human activities

the middle reaches of the Yellow River Basin (MYRB). In regions with intense human activities, the stationarity of runoff sequences was disrupted due to the dual impacts of climate changing and human activities. Therefore, establishment of non-stationary hydrological drought identification methods is urgently required. Previous research infrequently addressed the influence of indirect human activities on the non-stationary hydrological drought. This study comprehensively considered the impacts of climate change, direct human activities, and indirect human activities (underlying surface alterations) on runoff. Consequently, a non-stationary standardized runoff index (NSRI) was constructed based on the Generalized Additive Models for Location, Scale, and Shape, establishing a method for identifying non-stationary hydrological droughts in regions with intense human activities. This study uncovered the variability in hydrological drought characteristics in the major sub-basins of the MYRB, where human activities are intense, from 1960–2019.The results demonstrate that the non-stationary hydrological drought identification method constructed in this paper is feasible. The NSRI exhibits superior performance in identifying hydrological drought events across multiple timescales compared with the Standardized Runoff Index. In many sub-basins, the frequency of severe and extreme droughts across various time scales increased, with upward trends measured in both drought severity and intensity. The severity of hydrological drought in the MYRB may further intensify in the future. • A feasible method to identify non-stationary hydrological droughts in highly human-impacted regions is proposed. • NSRI construction comprehensively accounts for climate change , direct and indirect human activities' impacts on runoff. • NSRI exhibits an advantage in identifying droughts across multiple time scales. • Hydrological drought evolution in major sub-basins of the middle Yellow River over 60 years is revealed.