Comment on Liu (2020): A rational performance criterion for hydrological model

Abstract

The performance criteria have been often used in the hydrological model evaluation or calibration. Since the performance criteria have their own advantages and disadvantages, it is necessary to understand the impact of each performance criterion on the model evaluation or calibration to be used for the purposes of model applications. The Liu Mean Efficiency (LME) was proposed for the design flow estimates from hydrological modeling data by reformulating the three metric components (correlation, variability, and bias measures) in the Nash and Sutcliffe efficiency (NSE) or the Kling and Gupta Efficiency (KGE) to improve the flow variability in the runoff simulations optimized with the NSE or KGE. This article has discussed that the LME criterion has weaknesses of an underdetermined system that can potentially induce the vagueness in comparative assessments for alternative model performance as well as an overestimation system that can substantially reduce the reliability in design flow estimates through hydrological modeling. A complement approach to the limitations of the LME is necessary for the LME to be made fit for a rational performance criterion.