Hydrological modeling to predict streamflow under changing climate conditions in Upper Euphrates Basin

Under the influence of climate change, sustainable planning and management of water resources has become even more important worldwide. The effects of climate change in the Upper Euphrates Basin were investigated for RCP 4.5/8.5 scenarios based on regional climate models. Since the basin is in a mountainous area, the effect of climate change on both flow and snowmelt has been evaluated separately. Bias Corrections were applied for two different scenarios using four different regional climate models (CNRM-CM5/RCA4, EC-EARTH/RACMO22E, HadGEM/HIRHAM5 and NorESM1-M/HIRHAM5). Trend and anomaly analysis were conducted in 20-year intervals for the historical period (1970-2005) and the future period (2020-2100). A significant part of these scenarios was implemented in hydrological models (HEC-HMS and HBV-Light) to project the flow and snowmelt in the basin, with the aim of identifying and evaluating any significant variations or anomalies in the projected data. In the RCP 4.5/8.5 scenarios, it is observed that the temperatures tend to increase, while the precipitation tends to increase in some periods and decrease in others. As a result of hydrological modeling studies, NSE varies between 0.76-0.82 for calibration and between 0.70-0.75 for validation. As a result of the hydrological studies, a general increase in flow rates was observed. Based on the analysis of the effects of climate projections on snow melting, negative anomalies were observed in all models and scenarios for snow covered areas, snow water equivalent and number of snowy days. The results of the study show that for Karasu, which is a mountainous upstream basin, with increasing temperatures, precipitation will fall in the form of rain instead of snow, therefore, the number of snowy days, SWE, and snow-covered area will decrease, average flows will increase and the flow peaks will come to the fore in time. This means a decrease in snow feedings for the basin. It is seen that it is important to investigate the effects of decreasing snow on the related sectors and to include downstream basins in the study.