“…In the metaheuristic method, the objective function is expressed as the fitness value. The definition of the fitness value in the case of hydrological model parameter optimisation has been widely proposed by previous researchers, including minimisation of the root mean square error (RMSE) (Hsu and Yeh, 2015;Zhang X et al, 2012;Sulianto et al, 2018), minimisation of the sum square error (SSE) [Setiawan et al, 2003;Kim Oong H et al, 2005), maximisation of the Nash-Sutcliffe (NS) efficiency (Zhang et al, 2008;Bao et al, 2008;Uhlenbrook et al, 1999), the maximisation of the inverse mean square error (MSE) (Ngoc et al, 2012), minimisation of the relative error (RE) (Santos, 2011;Kuok King et al, 2011). In this article, the fitness value is expressed as the RMSE minimisation calculated by the equation:…”