Due to the importance of base flow in hydrologic processes and vital role in water resources management, estimation of base flow is an important issue. Graphical methods used to determine the base flow, significantly underestimate the contribution of this component. The results of isotopic and hydrochemical tracer methods in the humid regions, indicates a high proportion of groundwater component in runoff generation. The aim of this study is to investigate the role of groundwater flow in runoff generation processes in the arid and semiarid karstic Abolabbas basin, using isotopic techniques and hydrochemical tracers. For this purpose, during the winter of 2010-2011, three rainfall events with different antecedent moisture and intensity were selected and the corresponding floods were sampled. Hydrochemical parameters were measured in water quality laboratory of the water sciences faculty of Shahid Chamran University and Oxygen-18 isotopic content was measured in the stable isotope laboratory of Ottawa University. The results show that for all considered rainfall events, the contribution of groundwater component in runoff generation was considerably larger than the rainfall, due to karst development in the Abolabbas basin. The results also showed that the surface runoff component is minor for low moisture conditions, and it increases in the high moisture conditions.