D3.2. Multi-criteria decision analysis (MCDA) for selection and location of hybrid solutions

This deliverable 3.2 (D3.2) is the second one of the Work Package 3 (WP3) of the D4RUNOFF project. WP3 is divided in four tasks of six months each, with three deliverables in total. In this one, the work done during the third task is summarised in a public document open to comments and suggestions: a Multi-Criteria Decision Analysis (MCDA) for selection and location of hybrid solutions. This MCDA is mainly proposed for the selection of Nature-Based Solutions (NBS) used in urban drainage. The next deliverable (D3.3) will complete the WP3 adding the Geographical Information Systems (GIS) methodology with the final aim of selecting the best place for the NBS needed to improve the existing urban drainage conditions, resulting in hybrid systems. The principal objective of the D3.2 is to develop a tool for the prioritization of NBS as alternatives to implement into the existing urban drainage systems, resulting in hybrid systems. Firstly, the D4RUNOFF researchers have reviewed the literature, highlighting the main criteria used for NBS comparison. With this information and the participation of the water utilities involved in the project, together with other partners, the selection of attributes and criteria was done. Four attributes or categories of criteria were defined, three of which are alligned with the pillars of the sustainable development (economy, environment and society) and the fourth represents the current feasibility of the NBS (expertise). Then, the criteria were weighted to finally propose three different methodologies. The first one was the Analytic Hierarchy Process (AHP) and the results of the survey sent to a selected group of experts was the same as that obtained in an informal consultation conducted on the social media of the project: the environmental criteria are the most important. However, with the objective methodology that was finally proposed, the Entropy Weight Method (EWM), a higher weight was assigned to the economic criteria. The third weighting method gives the option of direct weighting to the decision maker. Afterwards, the definition of the indicators for each criterion was done considering mainly the D4RUNOFF Parametric Library (D3.1) but also other valuable references as the European Natural Water Retention Measures Platform. One of the main limitations of this MCDA is the quality and representativeness of the proposed indicators, that could be discussed and improved. For the final ranking of alternatives, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) was used, which provided different results depending on the weighting process. As conclusion, the two first positions correspond for both weighting methodologies to Wetlands and Green Roofs. This MCDA can be used openly thanks to the Excel spreadsheet developed for this purpose. From the results of this MCDA it can be stated that NBS can be prioritized according to different criteria, being possible and recommendable to combine them in order to offer a balanced, sustainable and realistic solution.