Comprehensive evaluation of hydrological drought and the effects of large reservoir on drought resistance in the Hun River basin, NE China

Abstract. Evolution of drought under changing climate and the operation of large reservoir play an important role in drought warning and control. Thus, the evolution characteristics of hydrological drought and the effects of large reservoir on drought resistance are explored in the Hun river basin (HRB). Firstly, Standardized runoff Index (SRI) was adopted to evaluate the evolution characteristics of hydrological drought. Meanwhile, based on drought duration and severity identified by the run theory, the copula function with the highest goodness of fit was selected to calculate the return period of hydrological drought. Furthermore, the propagation time from meteorological to hydrological drought were determined by calculating the Pearson correlation coefficients between 1-month SRI and multi-time scale Standardized precipitation index (SPI). Finally, based on the cumulative precipitation deficit thresholds for triggering hydrological drought, the impact of large reservoir on drought resistance of the basin was revealed. The results show that: (1) hydrological drought showed a slight strengthening trend in the eastern, while presented alternate characteristics of drought and flood in the western and center of the HRB from 1967 to 2019; (2) the western and center of the HRB were vulnerable districts to hydrological drought with longer drought duration and higher severity; (3) the most severe drought with drought duration of 23 months, severity of 28.7, and corresponding return periods that both exceed the thresholds of duration and severity and exceed the threshold of duration or severity were 371 years and 89 years, respectively; (4) the propagation time from meteorological to hydrological drought of the lower reaches of large reservoir has been significantly prolonged owing to the operation of large reservoir; and (5) the operation of large reservoir strengthened the drought resistance in the lower reaches while lightly weaken in the upper reaches of large reservoir.