Stormwater Treatment in Future Tropical and Sub-Tropical Climates

Stormwater treatment systems play an integral part in achieving sustainable urban development. The performance of these systems is likely to be impacted by potential changes in climatic patterns, including precipitation. This project investigates the simulated impacts of climate change on the performance of stormwater treatment systems used as a part of Water-Sensitive Urban Design (WSUD). Townsville and the Gold Coast of Queensland, Australia, were selected for the study to investigate tropical and sub-tropical climates experienced by cities across the globe adjoining sensitive coastal environments such as wetlands and coral reefs. The daily precipitation output projected by Coupled Model Intercomparison Project Phase 5 (CMIP5) climate models was downscaled to pluviograph input into the Model for Urban Improvement Conceptualisation (MUSIC). The treatment performance of bioretention systems and constructed wetlands was variable across both locations, with some models showing little to no change or improvement. Worsening of treatment performance was more prominent in the tropical climate, with numerous models reaching a decline of up to 16%. However, the highest observed reduction from a single model output occurred in the sub-tropical climate location. To make the WSUD treatment system effective under the future climate scenarios, physical modification is necessary to increase the treatment area or depth. Increasing the area in the worst-case scenario could incur a cost increase of 20% to 30% and present challenges due to development constraints. Increasing the depth could be a viable alternative for bioretention systems but is likely impractical for constructed wetlands.