Analyzing the Variability in Low-Flow Projections under GCM CMIP5 Scenarios

The present study considered the impacts of global climate model (GCM) selection in the Couple Model Intercomparison Phase 5 (CMIP5) scenarios on the low-flow projections for two representative concentration pathway (RCP) scenarios. The calibrated hydrologic model was applied to project future streamflow for Korean river basins using 13 GCMs and two RCPs (RCP4.5 and RCP8.5). A flow duration curve was constructed for each subbasin, and 75th percentiles of each period were considered as the thresholds for low flow. The results showed that there were high variabilities in the low-flow projections due to different internal variability within the GCMs. Some GCMs revealed a significant decrease in low-flow projections (IPSL-CM5A-MR scenario), and others showed a significant increase in low-flow projections (CanESM2 scenario). Selecting a few GCMs, including these extreme GCMs, can lead to different low-flow projections. The comparison of the climate projections for the primary GCMs revealed that the higher temperature and lower precipitation in the IPSL-CM5A-MR model than that in the CanESM2 model led to higher evapotranspiration and lower recharge of the underlying aquifer and, therefore, a significant decrease in the low-flow projection for the IPSL-CM5A-MR model. In addition, there were different uncertainties among the RCPs for the three future periods, which indicated that in addition to the dominant effect of GCM selection on low-flow projections, the selection of an RCP can have a major effect on the results.