Climate Change Impact on Combined Sewer Overflows

Combined sewer overflows (CSOs) have major impacts on receiving waters. It is important to investigate the potential impacts of climate change on CSOs. The main objective of this study was to develop projections on the future evolution of CSO frequency and durations in the context of climate change. First, a model was developed based on available CSO data (date of occurrence and durations over the May to October period for the years 2007 to 2009) from 30 CSO outfalls located in southern Quebec. This model estimates the probability of occurrence and the duration of a CSO given the rainfall total depth. Second, two simulated series from a regional climate model were used to estimate the evolution of CSO frequency and durations between 1961-1990 and 2071-2100 periods. Results suggest that the May to October mean CSO number will remain globally unchanged for the 30 CSO outfalls while mean annual CSO duration will slightly increase (+4.2%). On a monthly basis, CSO frequency and duration will decrease in average during July and August, while they will increase in May and October.