Assessing green roof hydrological performance during winter and rain-on-snow events under climate variability and change using high-resolution convection-permitting climate models

In an era characterized by urban densification and increasing pressures on urban space, along with the costs and availability of construction materials, the optimal design of infrastructure has become a critical focus. Furthermore, cold climate regions are experiencing the impacts of climate change, which manifest in altered precipitation patterns, resulting in more extreme storm events, including rain-on-snow events and increased freeze-thaw cycles. According to Maurin et al. (2024), rain-on-snow events have been identified as the leading cause of the highest observed runoff from green roofs, presenting significant challenges for urban areas in preventing flooding.

The present study aims to enhance understanding of the effects of climate variability and change on the hydrological performance of nature-based infrastructure, with a particular emphasis on green roofs during winter, especially in relation to snow and rain-on-snow events in cold climate regions. The goal is to develop guidelines that assist stakeholders in optimizing the design of nature-based solutions (NBS) infrastructure, ensuring they are resilient over time and effectively manage stormwater in a changing climate. This initiative addresses the current gap in research, particularly the lack of location-specific regulations that incorporate future climate projections for stormwater infrastructure design, giving decision-makers accurate information regarding the requirements for long-term and robust infrastructure design.

The study uses models of six different green and grey roof configurations developed in the SFI Klima 2050 project, calibrated for the winter season. These models utilize precipitation and temperature time series originated from high-resolution, convection-permitting climate models with hourly resolution and a 3x3 km gridded projection. Simulations for winter event separation (Melt, Rain and Rain-on-snow) are conducted following the methodology outlined in Maurin et al. (2024).

Results indicate that the changing climate will influence stormwater management strategies during winter, including higher runoffs of urban infrastructure due to rain-on-snow event with effects unevenly distributed across Norway (9 different cities studied). This pinpoints the need to combine the local future climate with hydrological models able to capture rain-on-snow events when planning and designing stormwater managements solutions that must remain effective under future climate scenarios. The findings have laid the groundwork for local guidelines aimed at ensuring climate-resilient design of nature-based infrastructure.

Maurin, N., Abdalla, E.H.M., Muthanna, T.M., Sivertsen, E., 2024. Understanding the hydrological performance of green and grey roofs during winter in cold climate regions. Science of The Total Environment 945, 174132. https://doi.org/10.1016/j.scitotenv.2024.174132