Systematic Assessment of the Development and Recovery Characteristics of Hydrological Drought in a Semi-Arid Area

Studies have documented the significant effect of various factors on hydrological drought events. However, few studies have quantified hydrological droughts' development and recovery process under environmental changes. This study focused on identifying hydrological drought's development and recovery characteristics and their potential causes in a typical semi-arid area. The standardized streamflow index (SSI) was used as a metric for hydrological droughts, while the run theory was applied to identify the development and recovery processes of droughts. Changes in observed (human-activity-scenario) and simulated (natural-scenario) droughts by employing the SWAT (Soil and Water Assessment Tool) model were also investigated from 1970 to 2016. The “simulated-observed” approach was used to assess the impacts of human regulations on hydrological drought development and recovery characteristics. Results showed that hydrological droughts occurred mainly during 1980-1990 and 2000-2016, and the human-disturbed scenario presents a more severe hydrological drought than the natural scenario. In the natural condition, the drainage basin characteristics of the basin played the most critical role in the development and recovery characteristics of drought, which was also influenced by climatic conditions. When considering the distribution of human activities, the reservoir operation was the dominant anthropic factor that affected the development and recovery process of drought in the study area. Under the effects of reservoir regulation, the long-duration hydrological droughts become rare. Moreover, the recovery ability of drought has been weakened. The effects of the reservoir will become progressively important as time goes on. Although the water intake from the river by the reservoir has been reduced, the negative impact on aggravating drought remains stronger than the reservoir was initially constructed. The results of our study will help improve the optimal management of reservoirs in semi-arid areas and enhance the drought early warning and forecasting system