## 4 Discussion and Conclusions  
Water is an important natural resource related to social and economic development and human survival, and it forms the basis for the formation and development of cities [36]. Owing to scientific and technological advances, seawater desalination [37] and reclaimed water [38] can be used to alleviate water scarcity. However, local waterworks that use river water often lack the facilities to monitor river flow, making it challenging to take preemptive actions such as restricting water intake volumes in the event of decreased river flow during a drought or dry season [39]. Therefore, it is necessary to analyze the drought conditions at WIPs, and to establish a drought assessment and response system for WIPs that lack observational data by using a long-term runoff model. Pursuant to Article 51 of the Korea River Act (PA51), the instream flow required to maintain the normal functions and conditions of rivers must consider domestic, industrial, and agricultural uses; environmental improvement; generation of electric power; and ship transportation. Accordingly, in this study, a method for assessing the number of days on which water can be extracted is proposed in order to expand and apply similar monitoring efforts nationwide and to establish water intake volumes that are appropriate for each \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Drought Index** & **No Possible Water** & **Water Shortages = [(WIC \(-\) WIC\({}_{\text{AVG}}\)) / |WIC\(|\)\(\times\) 100 (\%)** \\ (SPI or SDI) & **Intake Days** & & \\ (NPWIDs) & **>0** & **0 to \(-\)50** & \(-\)50 to \(-\)100 & \(-\)100 to \(-\)150 \\ \hline \(>\)0 & \(<\)15 & Normal & Attention & Caution \\ \(0\) to \(-\)1.0 & 15–30 & Attention & Caution & Alert \\ \(-\)1.0 to \(-\)1.5 & 30–45 & Caution & Alert \\ \(-\)1.5 to \(-\)2.0 & 45–60 & Alert & Status & Status \\ \(<\)\(-\)2.0 & \(>\)60 & & Status & Status \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Criteria for determining the drought conditions at ungauged water intake plants (WIPs). Figure 6: Water shortage and five-stage drought conditions for the Hyunri water intake plant (HWIP). river's maintenance or environmental flow. In addition, the outputs from a hydrological model based on the statistical downscaling of the KMA's global seasonal forecasting system version 5 can be utilized for drought forecasting, weather predictions, and long-term runoff analysis [40]. According to survey data from the National Drought Information Center, South Korea has 430 domestic and industrial water facilities among which 182 (42%) in 76 cities and counties utilize rivers as water sources. These include 109 riverbed water intakes (60%); however, corresponding flow observation data are only available for 65 WIPs. Therefore, in this study, the criteria for determining drought at ungauged river basins were determined by calculating WICs based on three data types (hydrological model, nearby measurement data, and hybrid method) and by evaluating WIDs and water insufficiency levels at WIPs. This study proposes a methodology for predicting and responding to drought evolution, specifically at locations that lack nearby data collection stations. The approach was tested at two pilot sites in South Korea, which has large numbers of ungauged water intake plants that lack local data collection facilities. Based on the findings of on-site surveys and candidate sites for the installation of watershed monitoring stations, the following drought management measures are proposed for ungauged riverbed WIPs. Additional observation facilities should be installed at ungauged riverbed WIPs as acquisition budgets permit. If there is a nearby water level-flow observatory, the DAR should be applied to determine the drought conditions, which should be based on available observation data observed prior to the installation of an observation station at the water intake site.