The potential of different NBS policies to provide water flow regulation. A scenario-based assessment based on SWMM.

Pluvial flooding is a growing concern in cities, exacerbated by climate change and rapid urbanisation. To address this issue, contemporary flood risk management focuses on urban resilience and the role of Nature-Based Solutions (NBS) in providing Water Flow Regulation (WFR). Using the Storm Water Management Model, this study explores the effectiveness of different NBS policies in a densely built municipality, Cormano (Italy). The research identifies green roofs and permeable pavements as key NBS options and assesses their performance under various rainfall conditions. Six policy scenarios are examined, ranging from 'direct' public policies, where the government directly implements NBS, to ‘enabling’ policies incentivising private stakeholders to adopt NBS. Results indicate that the ‘enabling’ policy yields the most significant WFR improvements in the case study. The study underscores the need for multifaceted, integrated, performance-based NBS strategies. It emphasises the importance of ‘enabling’ policy instruments, i.e. incentives for private retrofitting, in promoting NBS adoption.