Modeling the Impact of Watershed Physical Attributes on Surface Water Quality and Uncertainty Assessment Using the Monte Carlo Simulation Approach

Modeling of the relationship between physical characteristics of a catchment and water quality parameters plays a significant role in unified watershed management. In addition, in the process of modeling there is always an inevitable level of uncertainty caused by error in the input data, parameters and the structure of the model. Therefore, quantifying the uncertainty in the output of the model in order to reach certain forecasts in modeling is essential. In this research, water quality data, land use/cover, land suitability map and geological map of hydrometric stations located in the western part of the Caspian Sea were used. The modeling was done using Multiple Linear Regression Stepwise Method, while the model uncertainty analysis was examined using Monte Carlo simulation. Based on the results of the correlation and regression analyses, it could be concluded that all these parameters have a strong positive correlation with a variety of human activities such as agriculture and urban development. This indicated that an increase in agricultural land or a decline in forest areas will ultimately lead to a decline in water quality. The results of the Monte Carlo simulation shows that although some models have high R-squared values, the possibility of generation of negative outputs (Pr