Assessment and Optimal Management of Surface Water Resources in the Source of Upper Blue Nile River under Development and Climate Change Scenarios

Abstract

The objective of this study focuses on the assessment and management of surface water resources of Lake Tana Basin under development and climate change scenarios. Good hydrologic models are needed to manage water resources of the Lake Tana Basin, but model comparison studies have not been carried out for this area. In this study, the daily streamflows were simulated by applying two simple conceptual models and one physically-based, semi-distributed model for four major gauged catchments of the study area and compared their performances in both time and quantile domains. The best model in the time-domain can be applied for management and real-time operation, whereas the best model in the quantile-domain can be implemented for planning and climate change impact assessment. The calibrated parameters of the selected hydrological model were then transposed to the ungauged catchments by using the arithmetic mean, the physical similarity, the spatial proximity, and the catchment runoff-response similarity approaches. The catchment runoff-response similarity approach proposed by this study performed best for estimation of the surface water resources in the ungauged catchments. Furthermore, understanding the hydrological processes under changing climate is also crucial for future water resources planning and management in the study area, and thus this study inputted the three Representative Concentration Pathways (i.e. RCP 2.6, RCP 4.5, and RCP 8.5) to the selected hydrologic model with an appropriate statistical downscaling procedure. Lastly, this study developed an optimization model with a multi-objective genetic algorithm for optimally allocating the surface water resources to ongoing and planned water resources projects in the Lake Tana Basin. The model resulted in releases of more than 90% of the irrigation and hydropower demands for all baseline and future inflow scenarios. The optimization result also revealed that the Lake Tana water levels exceed the minimum Lake level (i.e. 1785 m) that required for navigation under all climate change scenarios. Keywords: Climate Change, Lake Tana Basin, Reservoir Operation, Ungauged Catchment Modeling, Water Resources Assessment