This paper applies HEC-HMS to the Karkheh River basin (KRB), Iran, and facilitates the calibration of a continuous hydrologic model (CHM) with soil moisture accounting (SMA) and snowmelt degree-day parameters. Manual calibration was performed to ensure the physical relevance of HEC-HMS parameter values. Because manual calibration entails changing each parameter value in a user-defined setting, it is often a time-consuming procedure complicated by multitude of interacting parameters. To address this setback, an event-based calibration technique (EBCT) was implemented in KRB and its interior sub-basins whereby the governing parameters of specific fall, spring, and winter events were initially estimated in a precalibration step and used as inputs to facilitate calibration of the CHM. Model performance analyzed based on goodness-of-fit criteria with respect to peak flows, low flows, and hydrograph shape reflects uncertainties associated with streamflow naturalization and use of average annual parameter values for the snowmelt component. Sensitivity analysis provided insights into the basin's snowfall and melt characteristics, distinguishing antecedent temperature index (ATI) cold rate coefficient and baseflow recession coefficient as key parameters affecting hydrograph shape and magnitude of the peak flow, respectively. Results based on goodness of fit metrics suggest that event-based parameter estimation using seasonal characteristics improved the efficiency and accuracy of the continuous HEC-HMS model (CORRL and NSE 0.78-0.87 and 0.5-0.7, respectively) while facilitating application to a large, data-poor river basin with heterogeneous climatic conditions.