The impact of SSP scenarios and hydrological model calibration data characteristics on future hydrological drought assessment

In this study, the impact of climate change scenarios and characteristics of hydrological model calibration data on the variability of future hydrological drought analysis in the upstream basin of the Seomjin River Dam was analyzed. Future climate data were constructed using 20 General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 6(CMIP6) and Shared Socioeconomic Pathway (SSP) scenarios (SSP2-4.5, SSP3-7.0, and SSP5-8.5). The Soil and Water Assessment Tool (SWAT) model was used to project future runoff. The length of calibration data and the hydrological conditions during the calibration period had significant impacts on the performance of runoff simulations. Notably, the hydrological conditions during the calibration period had a more significant influence than the length of the calibration data, and model performance improved when the hydrological conditions during the calibration and validation periods were similar. Future runoff was projected to increase significantly compared to the past during the spring season, especially under the SSP5-8.5 scenario. Differences in extreme runoff due to hydrological model calibration data were found to affect water resource management by an average 10%. In future hydrological drought analysis using the Streamflow Drought Index (SDI), differences in drought occurrence frequency were observed according to climate change scenarios, GCMs, and hydrological model calibration data. These differences were significant for droughts of 3-month duration, with the number of drought occurrences varying on average by 35.1 events and severe droughts by about 20.7 events, depending on the SSP scenarios, GCMs, and calibration data. The study results confirm the necessity of considering variability due to future climate data and hydrological models in hydrological drought analysis for future water resource management.