Improvement of CCME WQI using grey relational method

The conventional CCME WQI ignores the uncertainties in aquatic environment, which may lead to biases and abrupt changes in evaluation results. To overcome this shortcoming, this study improves the calculation of CCME WQI using trapezoid grey relational degree method, a model dealing with uncertainties introduced by incomplete information. Compared with the conventional CCME WQI, the grey CCME WQI has a stricter calculation method in synthetic evaluation and a better capacity in water quality warning. The water quality of New Tongyang Canal is evaluated and the result shows that its environment deteriorates with the increasing rainfall and improves with the decreasing precipitation. To decrease its environmental risk, it is suggested to reduce the nutrients in agricultural runoff and the oxygen-consuming pollutants in urban runoff in the rainy season.