COMPARISON OF HEC-HMS AND SWAT HYDROLOGICAL MODELS IN ESTIMATING RUNOFF IN HARE WATERSHED, SOUTHERN ETHIOPIA

Abstract

Hydrological models play a pivotal role in understanding runoff patterns, and among the widely utilized ones are HEC-HMS and SWAT. However, the performance of such hydrological models varies depending on the spatial and hydro-meteorological characteristics of the watershed. The objective of this study was to compare the performance of the two widely used hydrological models, HEC-HMS and SWAT, and hence to select best-suited model for simulating runoff in the Hare watershed, located in the Southern Ethiopia. The spatial data and daily hydro meteorological input data were utilized for both models. Sensitivity analysis, manual and automatic calibration and validation were carried out in this study. Flow data from 1999 to 2012 were used for the calibration, and the subsequent seven years (2013 to 2019) were used for model validation. Three statistical measures, Coefficient of Determination (R2), Nash-Sutcliffe Efficiency (NSE) and percentage bias (PBIAS) were used to evaluate the models performances. Accordingly, the result of this study indicates that the most sensitive parameter of HEC-HMS model were CN, Initial abstraction, Muskingum K and Lag time, whereas CN2 and ALPHA_BF were also the most sensitive parameters of SWAT model. The HEC-HMS model gave the model performance with the R2, NSE and PBIAS values of 0.76, 0.67 and 0.27 during calibration, and 0.81, 0.66 and -8.1 during validation, respectively. SWAT yielded the model performance with R2, NSE and PBIAS values of 0.64, 0.56 and 5.5 during calibration, and 0.62, 0.6 and -5.3 during validation periods, respectively. Therefore, it can be concluded that the simulated runoff by the HEC-HMS model is more satisfactory compared to the simulated runoff by SWAT model for Hare watershed. This study can be used as a baseline scenario for future watershed planning and management.