## 4 Discussion and Conclusions  
As climate change accelerates due to global warming, changes in hydrological cycles occur significantly, and water use and prediction of water resources may become difficult. In particular, in Korea, chronic drought has occurred continuously since the 1990s during the transition from winter to spring [46]. To cope with these droughs, technologies to identify and predict the magnitude of spatiotemporal droughs are required. Drought monitoring using satellite data will be essential to secure spatial resolution for accurate and spatial droughs when ground-based hydrometeorological data are not available, as well as monitoring the different characteristics of meteorological, agricultural, and hydrological droughs. Korea's drought-related affairs are mainly handled by the Korea Meteorological Administration (KMA), Ministry of Agriculture, Food and Rural Affairs (MAFRA), Ministry of Environment (MOE), Ministry of Land, Infrastructure, and Transport (MOLIT), and the Ministry of Public Safety and Security (MPSS) [47]. The KMA diagnoses precipitation and drought in drought areas by assessing the SPI and PDSI and provides this information to the local governments. The MAFRA analyzes agricultural water through the soil moisture index (SMI), reservoir drought index (RDI), and integrated agricultural drought index. The MOLIT monitors dam water; the MOE monitors emergency water resources and water quality according to the drought stage and implements the appropriate countermeasures. The MPSS oversees the drought situation when it becomes extreme. However, some point out that the current drought measurement indices of different agencies are different in drought management, causing confusion and making it difficult to respond to drought  
Figure 11: Drought condition changes in IBB simulation. (**a**) Case I (IDI\({}_{\text{normal}}\rightarrow\text{IDI}_{\text{Attention}}\)) and (**b**) Case II (IDI\({}_{\text{normal}}\rightarrow\text{IDI}_{\text{Caution}}\)). The simulation results for the five basin areas for up to three months are colored in the map. proactively. Different ministries have different standards for determining the degree of drought. Additionally, it is not sufficient for a single drought indicator to characterize all the complex drought evolution processes [22]. The development and application of an integrated drought index are necessary to take into account the complex factors related to water use, such as the meteorological, agricultural, and hydrological perspectives. Thus, this study proposed an RS-based integrated drought index that was extracted from 849 sub-basins in Korea's five major river basins using multi-sensor collaborative approaches and multivariate dimensional reduction models, calculated through monthly satellite data. Droughts in 2001 and 2014, representative years of severe drought since the 2000s, were evaluated using the integrated drought index, and statistical simulations were used to diagnose the sensitivity and transition of drought. The BPCA-based integrated drought index proposed in this study was analyzed to reflect the timing, severity, and evolutionary pattern of meteorological, agricultural and hydrological droughts, enabling comprehensive delivery of drought information. Although the results relied on limited observations, it is expected that drought hotspot analyses and statistical simulations using IBB and BPCA-based RSIDI will identify the drought characteristics of the sub-basin, thereby promoting their use in preemptive drought response through drought prediction and early warning. Drought monitoring and accurate drought forecasting are still the main challenges in a relatively changing environment that has a long lead-time and natural and artificial factors. Therefore, future works to improve drought monitoring and prediction require further research, such as high-quality data assimilation, improving model development through major processes related to droughts, selecting or predicting optimal ensembles, and hybrid drought forecasting.