Mainstreaming Nature-based Solutions in cities through performance-based planning: A case study in Trento, Italy

The aim of this chapter is to present and test a performance-based planning approach based on the information produced by ecosystem services (ES) mapping and assessment at the urban scale. The city of Trento in Italy is used as a case study. The planning approach allows to estimate the impacts of proposed urban transformations and to define for them appropriate and proportionate performances. These performances consist in the deployment of Nature-based Solutions (NbS) that can offset the negative impacts generated by the urban transformations. Particularly, the loss in the current ES supply defines the required level of performance, while the type of performance (i.e., what ES should be targeted by NbS) depends on ES demand. The approach is tested for selected transformation sites identified by the current City Plan and characterised by different existing and future land uses. The test is conducted by simulating how these sites could be developed to meet the requirements set by the performance-based approach while complying with the City Plan’s regulations. For each transformation, relevant NbS types and locations are proposed. Particularly, two different scenarios are designed for each site: a scenario aimed at achieving the minimum performance required by the approach (i.e., introducing only those NbS that are strictly necessary), and a scenario aimed at maximising the presence of NbS, and their benefits, in the available space. The impacts of the two scenarios are then assessed by considering the ES supply and the beneficiaries of NbS interventions. To this purpose, indicators to capture the potential changes with respect to the current condition are developed and applied. General findings suggest that meeting the requirements of the performance-based approach increases the supply of ES and the number of beneficiaries in both scenarios. The chapter further discusses strengths and challenges relevant to the application of this approach, such as the importance of the quality of the transformation design and the parameters used by planning authorities. Finally, the conclusion section explores the potential for adopting the performance- based approach as a planning tool and ways to strengthen its application, for example, by engaging citizens and residents on participatory grounds.