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Comparative study of a physically based distributed hydrological model versus a conceptual hydrological model for assessment of climate change response in the Upper Nile, Baro-Akobo basin: a case study of the Sore watershed, Ethiopia

ABSTRACT This paper presents a comparative study of two distinctively different hydrological models for simulating future discharge response in climate change scenarios. The mostly agricultural Sore watershed (1117 km²), Ethiopia, was used as a case study. Outputs from the climate models REMO (Regional Model) and CGCM3.1 (Canadian Global Climate Model) were used as inputs for hydrological models after statistical downscaling. Data from the REMO A1B and B1 and CGCM3.1 A1B scenarios were selected to represent future conditions. The models used in this study, the physically based distributed hydrological model WaSiM (Water Flow and Balance Simulation Model)-ETH and the conceptual model HBV (Hydrologiska Byråns Vattenbalansavdelning)-Light, were applied to simulate the flow conditions for a reference period (1990–1997) and a future period (2011–2050). The results confirm that the uncertainty caused by using different climate model inputs is larger than the uncertainty caused by using different hydrological models. In both hydrological models, the future peak discharge decreases in the future climate change scenarios regardless of the climate model and emission scenario considered. Whereas peak discharge shifted from August/September for the reference period to June in the future with CGCM3.1, discharge generally shifted to month earlier for both climate models. For low-flow conditions, the HBV-Light model always computed slightly higher values than the WaSiM-ETH model. This study demonstrates that both the hydrological and climate models were consistent concerning the overall direction of change, regardless of magnitude.