Urban parks and open spaces, forests, wetlands, green roofs and engineered stormwater treatment devices help manage stormwater and wastewater by reducing the volume of stormwater runoff, reducing surface flooding, and reducing contamination of runoff by pollutants . Engineered devices include bioswales, rain gardens, and detention and retention ponds, and are becoming common and standard approaches to mitigate the negative effects of impervious surfaces on stormwater quality and surface flooding in cities . Allotment gardens, street trees, green roofs and urban forests may also help reduce runoff and provide a stormwater retention service . Modelling and empirical studies show that NBS at small spatial scales lead to improvements in water quality and reduction of peak flows . Peak flow reductions are greatest for small rain events. For example, D-Ville et al.  observed a 30-70% reduction in peak flow for the 1-in- 30 year storm, but performance reduces for more intense rainfall or if saturated . Employing NBS to reduce flooding on roads can be an important adaptation mechanism for reducing the impact of flooding events on traffic flows .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report