## 1 Introduction  
Climate change from global warming can cause the modification of spatio-temporal patterns of future rainfall and runoff, thereby exacerbating the uncertainties stemming from the variability. In turn, such uncertainty strongly hinders management and planning to provide a stable water supply. Particularly in the 21 st century, droughts and floods have intensified. The development of new water resources is challenging, and from the increase in demand, it is evident that costs will increase as well, thereby exacerbating water-related problems, such as conflicts between stakeholders and regions over limited water resources [1]. In South Korea, most annual rainfall occurs in summer, but the rainfall pattern has already changed from bimodal, associated with the monsoon and typhoon, to a unimodal pattern. The frequency of rainfall events also exhibits an irregular pattern, thereby hindering accurate predictions. This, in turn, exacerbates management difficulties for multi-purpose dams to ensure a stable water supply [2]. Moreover, the occurrences of chronic droughts in spring and winter seasons have increased, and the amount of drought damage on a national or regional level has sharply increased as well [3]. Unlike other types of natural disasters, it is difficult to estimate the exact initiation and termination of a drought event. Moreover, drought is also characterized by its occurrence over a wide area, thus causing damage across an entire community or society. In addition, given the influence of climate change, the difference in precipitation between regions haswidened, leading to more localized, longer droughts that cause severe water shortages. On this basis, the South Korean government has been promoting short-term drought countermeasures, such as the development and securing of temporary alternative water sources for drought areas, planned distribution of water, and the management of water demand [4]. South Korea currently relies on multi-purpose dams for a substantial portion of its water supply. Specifically, the \"Water Supply Adjustment Standard for Reservoir Water Shortage\" has been implemented to minimize the impact on the lives of people even under the condition of insufficient rainfall in the dam basins in the future. The pilot launch of the established standard was initially carried out for two years for 15 multi-purpose dams nationwide, while the improvement (plan) for the standard was implemented in June 2016. The implemented improvement (plan) required that the standard reservoir storage be predetermined for a stage-specific drought response. Additionally, when the reservoir storage volume was below the standard reservoir storage at each drought stage, the drought stage was triggered, and water supply restriction was implemented [4]. In countries such as the U.S., the criteria for triggering and terminating the drought response stage are implemented according to various conditions, such as weather and hydrological conditions, and a maintenance period of the water level in reservoirs is also considered. For instance, for the Canyon Dam, located on the Guadalupe River (Texas, USA), the Guadalupe-Blanco River Authority has been formed. Additionally, to implement legal procedures for drought responses, the Authority issues a crisis alert for each drought stage according to the storage volume of a reservoir. It can also terminate a crisis alert according to the maintenance period of the storage volume above a certain level [5]. Moreover, the city of Corpus Christi (Texas, U.S.) classifies the drought stage based on the storage volume of the Choke Canyon Reservoir, Lake Corpus Christi, and Lake Texana in the upstream reach. Legally, it terminates the stage based on the maintenance period of the reservoir storage volume for each stage [6]. Setting termination criteria for drought response by stage enables minimizing negative impacts through flexible operation.