Dynamic analysis of drought propagation in the context of climate change and watershed characterization: a quantitative study based on GAMLSS and Copula models

Investigating the processes governing drought propagation under a changing environment is essential for advancing drought early warning and reducing socio-economic risks. Currently, few studies have analyzed the effects of meteorological factors and watershed characteristics on drought propagation based on non-stationary drought indices. In this paper, the probabilities and thresholds of meteorological drought to hydrological drought propagation were calculated using the non-stationary drought index constructed using the Generalized Additive Model for Location, Scale, and Shape (GAMLSS) model and the Copula function to assess the influence of large-scale climatic indices, meteorological elements, and watershed characteristics on the propagation characteristics of seasonal droughts. The results showed that non-stationary drought indices that incorporate meteorological factors tended to have a better performance than standardized drought indices. Under the combined influence of large-scale climatic indices, temperature, specific humidity, and wind speed, the propagation probabilities became larger especially during spring and winter in the upstream and midstream regions of the Luanhe River Basin, China, with the propagation thresholds in winter significantly increases by 0.1–0.2. These mean that hydrologic droughts are more likely to be triggered. Furthermore, the spatial variability of drought propagation is further influenced by watershed characteristics, including the slope and leaf area index, which collectively alter runoff generation processes.