Analysis of propagation thresholds and impact mechanisms from meteorological drought to hydrological drought in the middle and upper reaches of the Han River Basin, China

Drought propagation from meteorological drought (MD) to hydrological drought (HD) involves a temporal delay driven by multiple determinants and complex response dynamics and poses substantial challenges to river basin drought management. This study investigates the MD-HD drought progression in the Upper and Middle Han River Basin (UMHRB). We quantify the duration and intensity of drought propagation and establish the MD propagation thresholds triggering HDs under different drought categories. Furthermore, this study analyzes how meteorological variables and land surface conditions modulate drought progression and employs the coupled water-energy balance equation to reveal the underlying mechanisms influencing drought propagation. HD events generally followed MD episodes, with propagation thresholds for the UMHRB were determined via Bayes’ theorem. The results indicate spatially decreasing sensitivity of HD to MD from upstream to downstream in the UMHRB. Temperature emerged as the predominant factor influencing drought progression, whereas precipitation and potential evapotranspiration (PET) showed secondary effects. Additionally, watershed’s physical characteristics and anthropogenic activities, which significantly correlated with the parameters ω of the coupled water-energy balance equations, also modulated drought propagation. However, the parameter ω failed to fully represent the influence of human activities in the Huangzhuang section, suggesting a limitation that could be addressed by integrating factors pertinent to drought progression.