Urban flash floods occur in North America and worldwide due to extreme rainfall events, defined as high intensity rainfall in a short period. The growing frequency of extreme rainfall events is attributed to climate change and urban development. Thus, it is imperative to proactively implement enhanced stormwater management measures to better address these challenges. This paper presents preliminary data on the hydrological performance of NBS-VRA, which was evaluated through in-laboratory experimental testing and natural field monitoring. The experimental program comprised an 8 × 12 ft rain simulator designed to simulate predetermined rainfall events on NBS-VRA. The natural field monitoring was conducted on a rooftop of a test facility at the National Research Council Canada's Ottawa Campus to monitor daily natural rainfall events and substrate moisture changes from June to September 2023. The experimental testing on the storm simulator was conducted to investigate the effect of low (0.5 mm/min), high (3 mm/min) and extreme (6.6 mm/min) rainfall intensities on their hydrological performance. The retention capacity of the tested modules is compared with a standard roof with no vegetation. Moreover, the impact of initial moisture content (IMC) and moisture changes (MC) were also assessed in the experimental and field monitoring. Results illustrate that the retention performance of NBS-VRA is highly influenced by rainfall intensity and the initial moisture content. VRA with lower IMC has a higher retention capacity. NBS-VRA is highly effective in reducing peak runoff during extreme events. However, its hydrological effectiveness tends to decrease after successive rainfall events.