Assessing the impact of green roofing on stormwater management in urban areas

Abstract

Urbanisation has significantly increased impervious surfaces such as rooftops, pavements and roads, altering natural hydrological pathways and exacerbating stormwater runoff volumes and peak flows, thereby increasing flood risk in urban areas. Nature?based infrastructures like green roofs offer a promising mitigation strategy, intercepting, storing and slowly releasing rainfall from rooftops and thereby reducing downstream pressures on drainage systems [1-5]. However, while existing studies demonstrate meaningful retention and attenuation benefits under specific conditions [6-8], there remains limited empirical data on how such systems perform across varied climatic zones, substrate types, vegetation assemblages and retrofit scenarios [4, 9], leading to uncertainty for urban planners and water?resource managers. The problem statement of this research is: stormwater management systems in dense urban areas face escalating load due to increased imperviousness and intensifying rainfall, while the adoption of green roof systems is hampered by insufficient region?specific performance data and unclear design guidance for stormwater mitigation. Accordingly, the objectives of this research are: 1. To quantify the volumetric reduction of stormwater runoff achieved by green roofing systems in an urban area; 2. To evaluate the degree of peak flow attenuation during intense rainfall events provided by such systems; and 3. To assess runoff quality improvements (in terms of pollutant loads) from green roofs compared to conventional roofing surfaces. We hypothesise that green roofing systems will: · (H1) Significantly reduce total runoff volume compared to conventional roofs; · (H2) Lower peak flow rates during storm events; and · (H3) Produce runoff with reduced concentrations of key pollutants (e.g., total suspended solids, nutrients, heavy metals) relative to conventional roofs. By testing these hypotheses, this research aims to fill a critical gap in knowledge and support evidence?based adoption of vegetated roof systems as part of urban stormwater management frameworks.