The impacts of climate change and urbanisation on drainage in Helsingborg, Sweden: Combined sewer system

SummaryAssessment of the potential impact of climate change on water systems has been an essential part of hydrological research over the last couple of decades. However, the notion that such assessments should also include technological, demographic and land use changes is relatively recent. In this study, the potential impacts of climate change and continued urbanisation on waste and stormwater flows in the combined sewer of central Helsingborg, South Sweden, have been assessed using a series of DHI MOUSE simulations run with present conditions as well as two climate change scenarios and three progressive urbanisation storylines. At present, overflows of untreated wastewater following heavy rainfalls are a major source of pollution to the coastal receiving waters and there is a worry that increased rainfall could exacerbate the problem. Sewer flows resulting from different urbanisation storylines were simulated for two 10-year periods corresponding to present (1994–2003) and future climates (nominally 2081–2090). In all, 12 simulations were made. Climate change was simulated by altering a high-resolution rainfall record according to the climate-change signal derived from a regional climate model. Urbanisation was simulated by altering model parameters to reflect current trends in demographics and water management. It was found that city growth and projected increases in precipitation, both together and alone, are set to worsen the current drainage problems. Conversely, system renovation and installation of sustainable urban drainage systems (SUDS) has a positive effect on the urban environment in general and can largely allay the adverse impacts of both urbanisation and climate change.