The potential for rendering porous the watertight ground surface of Parisian public space has been identified by considering a certain number of hypotheses which are shown below and organised under 3 main leverage groups which can be activated by the community: creating continuous lines of trees, converting on-street parking spaces and developing singular places. A fourth leverage point was also identified, based on the initiative of citizens, which involves the removal of asphalt at the foot of facades, leading to asphalt removal permits being granted. These are all shown in detail below. However, two constraints were taken into consideration: the ground surfaces of food markets being systematically excluded from this plan of action for sanitary reasons, also the constraints linked to underground work in the métro were taken into account by identifying areas less than 5 metres from the work-sites as being precarious. So, taking into account this latter constraint gives an estimated 252 ha of potentially permeable ground (compared with 269 ha if this constraint is not implemented).
