Multi-objective optimization of rainwater infiltration infrastructures along an urban–rural gradient

Abstract

Many cities are developing infiltration infrastructures aimed at restoring natural hydrological processes. Among those, Nature-Based Solutions (NBS) can generate co-benefits, which contribute to cities’ adaptation to climate change. However, choosing optimal locations for infiltration infrastructures within limited available urban space is a complex spatial problem. It requires taking into account spatial patterns of infiltration potential as well as urban-rural gradients of costs and benefits. To address this, we apply a multi-objective optimization on a simple monocentric model city designed to give generic insights into location choices. We test a series of hypotheses: in comparison with a reference situation, we test the impact of the impossibility to infiltrate rainwater in city centers, the impact of substitution effects due to the presence of urban parks, and the possibility to mix NBS with grey infrastructures. The solutions reveal two polar strategies: locating infrastructures in the city center with higher co-benefits despite higher opportunity costs, or selecting suburban locations with the highest infiltration potential and lower opportunity costs - and a diversity of hybrid solutions. Substitution effects lead to discarding locations near urban parks, especially in centric locations. Finally, mixing NBS and grey infrastructures leads to a specialization of solutions by area and the potential to reach higher benefits at less opportunity costs.