Exploring green infrastructure planning through catchment modelling with stakeholder-informed scenarios

ABSTRACT Urbanization and climate change are putting pressure on urban drainage systems, particularly in cities with aging combined sewers. This study evaluates the effectiveness of green infrastructure (GI) in reducing combined sewer overflow (CSO) durations and pollutant loads under current and future climate conditions. Using a spatially realistic, stakeholder-informed implementation approach, the study addresses modelling uncertainty, evaluation of practical GI implementation strategies, and identifies subcatchments contributing to pollutants in the overflow. An ensemble-based hydrological model and a simplified pollutant load assessment were applied to an urban case study in Trondheim, Norway, using scenarios developed in collaboration with local stakeholders to implement bioretention cells in the catchment. Results showed that GIs limited to public land can reduce CSO durations by up to 63% under the current climate and 65% in the future climate. Evaluation of pollutant loads from critical subcatchments highlighted areas for additional water quality benefits. The study demonstrates that stakeholder-informed modelling provides practical insights for municipalities and supports the development of integrated stormwater management plans.