Application of Modified Cloud Model-Level Eigenvalue Method in water quality evaluation

Groundwater quality is affected by numerous uncertain factors, and the evaluation process is liable to randomness and fuzziness. To evaluate the quality of groundwater effectively, this study proposed a multi-index evaluation system termed the Modified Cloud Model-Level Eigenvalue Method (MCM-LEM) model, which is based on cloud model theory. In this evaluation system, the water quality was classified into five levels and several parameters were selected, while the CRITIC objective weight method is used to calculate the weight of each evaluation parameter, before an One-dimensional Normal Cloud Model and a Multi-dimensional Normal Cloud Model are established to obtain the membership degree of water samples pertaining to each water quality level. Finally, the LEM was used to assess the water quality level. In this study, taking the groundwater in the urban area of Jilin City as an example, seven evaluation parameters were selected for water quality evaluation, and the water quality evaluation results using the MCM-LEM model were compared with those obtained via the Single Factor Evaluation Method, the Nemerow Index Method and the Fuzzy Comprehensive Evaluation Method. The evaluation results obtained via the MCM-LEM model were largely consistent with those obtained via the other methods. Compared with the other methods, the MCM-LEM model can comprehensively consider the fuzziness and randomness, as well as the correlation between them; can avoid complex function calculations; and can provide more scientific and objective evaluation results. Furthermore, compared with the One-dimensional Normal Cloud Model, the Multi-dimensional Normal Cloud Model comprehensively considers multiple evaluation parameters, which simplifies the modeling process and reduces the calculation times for the membership degree. Meanwhile, using the LEM to determine the water quality level not only overcomes the inapplicability of the Maximum Membership Degree Principle, but also allows for assessing the relative advantages and disadvantages of different water samples of the same level. The proposed method can be used to the evaluation of the groundwater quality in other areas, enabling the planning and management of groundwater resources.