Estimating Future Changes in Streamflow and Suspended Sediment Load under CMIP6 Multi-Model Ensemble Projections: A Case Study of Bitlis Creek, Turkey

Abstract

The Euphrates-Tigris River Basin, which spans Turkey, Syria, Iraq, and Iran, is one of the most vulnerable zones to climate change. This study quantifies the impacts of changing climate on streamflow and suspended sediment load rates in the most threatened highlands region of the Euphrates-Tigris Basin, with the case of Bitlis Creek. In this evaluation, the multi-model ensemble approach is utilized to produce precipitation and temperature projections by analyzing the simulation performances of 24 global circulation models (GCMs) from the coupled model intercomparison project phase 6 (CMIP6). The Soil and Water Assessment Tool (SWAT) is used to estimate future streamflow and suspended sediment load rates over 25-year periods under the medium- and high-forcing shared socio-economic pathway (SSP) scenarios of SSP2-4.5 and SSP5-8.5. The results illustrate that the mean annual streamflow and suspended sediment load rates are expected to decrease by up to 8.5 and 21.4% under the SSP2-4.5 scenario, and by up to 20.9 and 40.7% under the SSP5-8.5 scenario, respectively. The projected shift from snowy to rainy winters leads to significant increases in winter streamflow and suspended sediment load rates, anticipated to reach 39.1 and 73.5%, respectively, during the 2075–2099 period for the SSP5-8.5 scenario. In contrast, declines in spring streamflow and suspended sediment load rates are projected to reach 40.9 and 60.0%, respectively, during the same period under the SSP5-8.5 scenario. These results suggest that the riparian countries should incorporate adaptive measures into their water resources management plans to ensure a sustained water supply in the coming decades.