4.1.2. Type/Scenario Evaluation

The type/scenario evaluation should set up preliminary, optional GSI scenarios based on the actual situation of planning areas after determining the ES requirements during the objective formulation step. These options may involve a combination of various types of GSI, where the opinions of experts who are familiar with related fields and planning areas are instrumental. The key to this planning step lies in the selection of evaluation criteria and their weight determination. The evaluation involves multiple dimensions, so the adopted and feasible approach is to build frameworks of MCDA [32,62,85] to integrate the selected criteria and their weights for evaluating the performance of the GSI types or scenarios and determining the best one. As an alternative to conventional methods, GSI makes up for their low level of sustainability [10], and the entire life cycle of GSI, i.e., planning, implementation, operation, and maintenance, is related to multiple dimensions of society, economy, and environment; thus, we recommend that the criteria system of evaluation frameworks should cover the three dimensions of social sustainability, economic sustainability, and environmental sustainability, so that the most favorable option for the comprehensive sustainability encompassing the above three dimensions can be identified, which is feasible and advantageous. Based on the reviewed articles, we enumerate reference evaluation criteria (Table 3) for social sustainability, economic sustainability, and environmental sustainability, which can provide guidance for related planning. Actual planning may assign the criteria subjectively and objectively; for example, the environmental and operational criteria in the planning of Hua et al. [62] are assigned by subjective judgments of the authors, while other indicators are assigned through simulation or calculation, which does not mean that these values are accurate enough. When assigning ES criteria in the evaluation system, the inability to accurately quantify the relationship between GSI and ES reduces its accuracy, which is similar to the defects pointed out in the step of objectives formulation and also emphasizes the urgency of quantifying the relationship between GSI and ES.

**Table 3.** Example criteria to evaluate the social, economic, and environmental sustainability of the alternative scenarios.


As regards the determination of criteria weights, analytical hierarchy process (AHP) or AHP-based integrated methods are often used [32,62,85], which have been widely utilized to evaluate decision criteria for various topics [86]. AHP is a simple tool for MCDA but with a certain degree of subjectivity. Conventional AHP cannot provide decision making for uncertain issues based on subjective judgment; therefore, scholars have made some efforts to remedy this, such as using improved AHP to cope with the subjectivity inherent in human judgment [32,85]. In addition, the decision of the type/scenario evaluation still needs to be verified to ensure that it can be conducted in practice, which means the options should be verified through case studies and communication with decision makers in the future.
