Assessing cost-effectiveness of nature-based solutions scenarios: Integrating hydrological impacts and life cycle costs

Nature-based solutions (NBS) as a sustainable strategy has recently received increasing attention for urban stormwater management. Thus, an evaluation of cost-effectiveness of NBS scenarios by integrating hydrological impacts and life cycle costs is significant for the decision-making process. This study first investigates the hydrological responses of a 5.2 km² semi-urban watershed under various implementation NBS scenarios and highly spatially variable rainfall fields. The fractal dimension is considered as a scale invariance indicator to quantify the heterogeneous spatial distributions of NBS in each scenario across a range of scales. The hydrological responses of NBS scenarios are assessed by the fully distributed and physically based model (Multi-Hydro) under different rainfall conditions with a high spatial resolution of 10 m. In order to assess the cost-effective NBS scenarios, the hydrologic indicator (reduction of peak flow and total runoff volume) is integrated with the economic indicator (life cycle costs). The results show that the optimal NBS scenarios are characterised with fractal dimension ranges from 1.5 to 1.6 under all studied rainfall events. Considering the NBS scenarios under the strongest rainfall event, concentrating NBS downstream of the catchment can be more cost-effective. This study can provide some guidelines for the decision-making process on sustainable urban planning and improve the flood resilience of cities.