The present study develops a reliability assessment method of wind resource using optimum reservoir target power operations that maximizes the firm generation of integrated wind and hydropower. A combination of water resources model for a system of reservoirs that implements a demand-priority based linear programing algorithm and a single node power grid system model is implemented on hourly time step. This model was accompanied by a global genetic algorithm solver to determine optimum operation targets for each storage reservoir aiming at maximizing the 90th percentile power generation produced by the integration of wind and hydro over the entire simulation period. This model was applied on the reservoir storages and hydropower system in the Zambezi river basin to test if the storage reservoirs could be efficiently be used to offset wind power intermittence in South Africa subjected to the different physical and policy constraints. Based on the optimized target operation and hourly annual real data for the year 2010, the water resources system and power interconnection system were simulated together to assess the maximum firm generation of power as a result of the new wind and hydro combination target for storage hydropower plants. The result obtained indicates that high regulation of wind and hydro can be achieved as a result of combined operation and showed 45% increase in the level of wind penetration in South Africa's power system over the reference scenario. The result also indicated a reduced level of coal power utilization and less cycling requirement. This will have a positive outcome in terms contributing to South Africa's goal toward reducing greenhouse gas emission and the efforts to build green energy supply and resilience to the impacts of climate change. (C) 2015 Published by Elsevier Ltd.