## 3 Results
### Drought Transition Evaluation by Statistical Simulations  
This study simulated the impact on the spatiotemporal distribution of different drought conditions, such as agricultural and hydrological perspectives, by altering the intended difference of \(\delta_{\mu}(r)\) (Equation (11)) of the meteorological drought index (SPI) 1000 times to represent the changes in SPI. As \(\delta_{\mu}(r)\) was intentionally changed, all the sub-basins experienced various changes in their ADCI and WBDI. Figure 9 shows that statistical simulations indicate that the changes in the state of agricultural (ADCI) and hydrological (WBDI) droughts correspond to the changes in meteorological drought (SPI). In addition, the results of the IBB simulation for up to three months of a lagged analysis were shown in Figure 10. Natural disasters, including droughts, are managed in four stages (Attention, Caution, Alert, and Serious) in Korea. In this study, the changes in other drought conditions were identified by intentionally changing the meteorological drought condition by using a IBB simulation. First, when the meteorological drought (SPI) conditions were simulated from a stage of Normal to a stage of Attention (Figures 9a and 10a), the ADCI conditions, except for some parts of the Han River basin, showed a stage of Attention (96.6%, 820 out of 849 sub-basins). According to the results of the one-month delay, the ADCI status in parts of the Han and Nakdong River basins changed to Normal; however, 77.1% of the entire basin (45.8% of the two-month delay) was still in a stage of Attention. Over time, the ADCI conditions have shifted from a state of Attention to Normal in the southwestern part of the Han, Youngsang River, and Sumjin River basins. Even if the SPI conditions are simulated from the Normal stage to a stage of Attention, the results of the SPI are similar to those of time and space, and there are many sub-basins that are converted to the Normal stage over time. When the meteorological drought (SPI) conditions were simulated from the Normal stage to a stage of Caution (Figures 9b and 10b), excluding the parts of the Han River basin, more than 98.6% showed the ADCI to be in the Attention stage and 15.9% showed a stage of Caution. According to the results of the one-month delay, the ADCI in the northern parts of the Han River was still in a state of Caution; however, 88.5% of the  
Figure 8: Spatial change of each drought index: SMSI, VCI, TCI, and ADCI for the 2014 drought. entire basin was in the stage of Attention. Over time, the ADCI conditions shifted from a state of Attention to Normal in the southwestern parts of the Han, Youngsan, and Sumjin River basins. Although the mid-term drought (SPI6) was simulated from a Normal stage to a stage of Attention, changes in the spatiotemporal pattern of the ADCI were similar to the results obtained for SPI3, in which the scope of Attention conditions was reduced, and the number of sub-basins converted to \"Normal\" over time increased in the southern parts of the country. For WBDI, when the SPI drought conditions were simulated from Normal to a stage of Attention, the WBDI conditions, excluding the Han River basins, showed a stage of Alert (99.2%, 842 out of 849 sub-basins). As a result of the one-month delay, the WBDI status shifted from 75.7% of the total basin to a state of Attention, but 50.7% of the Han River basin and some areas of the Geum and Youngsan River basins were still in Caution levels. Over time, the WBDI conditions tended to shift from a state of Attention to Normal in the southwestern parts of the Han and Geum River basins. The SPI drought conditions were simulated from Normal to Caution; more than 93.8% of the total basins showed their WBDI in a stage of Caution. Over time, the WBDI status shifted to a Normal state around the southwestern Han and Geum River basins.