## 2 Materials and Methods
### Pilot Site and Hydrometeorological Data  
Criteria were established for the determination of drought conditions at water intake points based on the analysis of observation data and hydrologic models of pilot locations (Figure 3). The first site, Hyunri water intake plant (HWIP), is located in Gangwon Province, South Korea. The plant was completed in 1997 and takes water from Batanea Stream. The facility has a capacity of 3300 m\({}^{3}\)/day, a minimum water intake of 1525 m\({}^{3}\)/day, a maximum water intake of 3136 m\({}^{3}\)/day, and an average daily water intake of 2383 m\({}^{3}\). A shallow well is utilized for water intake and the water level and flow are observed at the nearby Hyunri Bridge. The National Water Management Information System (WAMIS) of Korea provides real-time river water level and flow data (observatory code 1012640) from 2014 to 2020 for the HWIP. However, 18.2% of the data are missing because of freezing during winter; therefore, for the analysis of the FDC, intake calculations were compared using the following two methods; (1) existing data measurements were compared with the simulated daily runoff derived from the Tank model; and (2) simulation results were used to substitute for data that were missing owing to freezing. As the water intake point and water level observatory are in close proximity, the DAR was not separately applied.  
The second site, Chungsan water intake plant (CWIP), is located in North Chungcheong Province, South Korea. Riverbed water enters through a catchment conduit from the Bocheong Stream, with a facility capacity of 1000 m\({}^{3}\)/day and average daily intake of 602 m\({}^{3}\) as of 2018. Water levels and flow data observed at the nearby Sangae Bridge (observatory code 3007660) were obtained from the WAMIS (2007-2020). Given the separate locations of the CWIP and water level observatory station, the average low flow volume was calculated by applying a DAR of 0.81 based on the ratio of the respective drainage areas.  
In this study, the drought conditions were determined based on the lack of water at supply facilities, considering the average daily intake of each facility. Depending on the state of the water source, water intake volumes may be present at nearby water level observation stations, enabling the straightforward calculation of the water level and flow relationship curve, and thus the quick determination of water shortage at each supply facility. However, the water level and flow observation stations associated with most local water sources are located downstream of the basin, making it relatively more challenging to calculate the water shortage at a given supply facility. Thus, in the present study, the water supply volume was calculated by applying a DAR, considering the surface area of the water source and reference area of the water level observatory. However, if the water level observation station was not located nearby, or if measurement data were missing, the discharge amount was simulated using the Tank model built by K-water; that is, localized parameters were applied to calculate the water quantity using a rainfall-runoff model. Finally, LF was calculated based on the FDC obtained from the simulated daily runoff analysis. In addition, the meteorological drought index was calculated based on the standardized precipitation index (SPI) provided by the Korean Meteorological Administration (KMA). The SPI was developed by [PERSON] et al. (2005) and is the most used drought index, owing to its simple calculation and ability to evaluate drought at different time scales. The SPI value is based on rainfall observation stations. Thus, if the intake site basin is located at the boundary of the Theisen network, the spatial weighting factor of the polygon that includes the water intake site is used to calculate the SPI.