Evaluation of Different Objective Functions Used in the SUFI-2 Calibration Process of SWAT-CUP on Water Balance Analysis: A Case Study of the Pursat River Basin, Cambodia

Davy Sao,Chantha Oeurng,Tasuku Kato,Le Hoang Tu,Panha Thouk,Atiqotun Fitriyah

doi:10.3390/w12102901

Abstract

Many calibration techniques have been developed for the Soil and Water Assessment Tool (SWAT). Among them, the SWAT calibration and uncertainty program (SWAT-CUP) with sequential uncertainty fitting 2 (SUFI-2) algorithm is widely used and several objective functions have been implemented in its calibration process. In this study, eight different objective functions were used in a calibration of stream flow of the Pursat River Basin of Cambodia, a tropical monsoon and forested watershed, to examine their influences on the calibration results, parameter optimizations, and water resources estimations. As results, many objective functions performed better than satisfactory in calibrating the SWAT model. However, different objective functions defined different fitted values and sensitivity rank of the calibrated parameters, except Nash–Sutcliffe efficiency (NSE) and ratio of standard deviation of observations to root mean square error (RSR) which are equivalent and produced quite identical simulation results including parameter sensitivity and fitted parameter values, leading to the same water balance components and water yields estimations. As they generated reasonable fitted parameter values, either NSE or RSR gave better estimation results of annual average water yield and other water balance components such as annual average evapotranspiration, groundwater flow, surface runoff, and lateral flow according to the characteristics of the river basin and the results and data of previous studies. Moreover, either of them was also better in calibrating base flow, falling limb, and overall the entire flow phases of the hydrograph in this area.

Highlights

Several distributed hydrological models have been increasingly and widely employed, which are extremely essential to simulate hydrological phenomena, to manage and plan water resources, to investigate sedimentation and water quality, and to forecast the impact of universal climate and land-use changes
We aimed to identify a proper objective function which produced reasonable calibration results, calibrated parameter sets, and water resources estimations which reflected the characteristics of this river basin
The results showed that the estimated water balance components and water yields differed by the the ratios of estimated annual average deep aquifer recharge (DAR) and amount of types of objective functions used

Summary

Introduction

Several distributed hydrological models have been increasingly and widely employed, which are extremely essential to simulate hydrological phenomena, to manage and plan water resources, to investigate sedimentation and water quality, and to forecast the impact of universal climate and land-use changes. The Soil and Water Assessment Tool (SWAT) is one of the most well-known and has demonstrated its strengths in the above aspects with a large and growing number of model application in various studies ranging from catchment to continental scales [1,2,3,4,5] It is open source software developed by the U.S Department of Agriculture (USDA) Agricultural Research. This physically based, watershed-scale, continuous model is commonly applied for measuring the impact of land-use and climate changes and for determining the different watershed management activities on hydrology, sedimentation, and water quality [6,7,8,9,10]. The SWAT calibration and uncertainty program (SWAT-CUP) links sequential uncertainty fitting 2 (SUFI-2), generalized likelihood uncertainty estimation (GLUE), parameter solution (ParaSol), Markov chain Monte Carlo (MCMC), and particle swarm optimization (PSO) algorithms to SWAT [12]

Methods

Results

Discussion

Conclusion