The study area of suluh catchment have the scarcity of record data, but the Suluh River havernthe capability of feeding the society nearby as source of small scale hydropower and irrigation.rnIn addition to that since it is ungauged catchment it has no representing model of Rainfall-rnrunoff relation and water harvesting structure. The work described here will attempt to solvernthese problems using the regional approach whereby statistically homogeneous regions arernidentified and the parameters of choosing distribution are estimated from the regional averagesrnso that the flow quantile for the ungauged catchment within that region can easily be computed.rnSo that the necessity of this study arises from the weight to improve site specific estimatesrnbased on limited data and to make inference about ungauged catchments. rnIn ungauged catchments, model parameters have to be estimated from other sources ofrninformation. An appealing way to estimate model parameters in ungauged catchments is tornglean the model parameters from hydrologically similar catchments. Hydrological modeling inrnungauged catchments often involves the transfer of calibrated model parameters from donorrn(gauged) catchments to the receiver (ungauged). However, in any hydrological modeling, some parameters tend to be more sensitive to the objective function, whereas others arerninsensitive. Sensitivity analysis was performed to choose the most sensitive flow parametersrnthat influence the catchment represented by SWAT to be used for calibration. This wasrnachieved using the global sensitivity approach in semi-automated Sequential UncertaintyrnFitting (SUFI2) algorithm. The global sensitivity analysis method takes into consideration, thernsensitivity of one parameter relative to the other in order to give their statistical significances.rnThe t-statistics and p-values of the parameters were used to rank to the different parametersrnconsidered to influence flow and the final selection done based on the significance of the rankedrnvalues. Table4 shows stream flow parameters that were tested for their sensitivity. These arernuseful in estimating the amount of flow from a catchment. The global sensitivity analysis of 21rnflow parameters showed that, only eight were very sensitive to flow. Although, the rest of thernparameters were found not to be sensitive to flow in the catchment as their p-values wererngreater than 5%. The Time period of 2000-2009 is used for SWAT model Calibration, and thern2009-2014 period for validation. Time series plots, as well as statistical measures, such as therncoefficient of determination (R2) and the Nash-Sutcliffe efficiency (NS) parameter betweenrnobserved and simulated stream flows are computed on monthly time scales and indicate a goodrnperformance of the final calibrated SWAT model. From the SWAT model output around 85%rnof the Suluh flow indicates surface runoff. rnThe maximum rainfall of the catchment is about 331mm during a month of August andrnSimilarly with surface runoff of 98.3mm.