When It Rains, It Pours: Climate and Waterborne Disease Transmission in Urban Coastal Ecosystems

Urban coastal regions face unique challenges in managing and protecting water resources.  This is particularly true in the Great Lakes, which serve as the drinking water source for more than 40 million people and have more than 500 beaches. The Great Lakes are heavily impacted by combined sewage overflows, and 140 communities release nearly 150 billion liters of combined sewage each year.  The major threat of sewage overflows is due to the release of pathogens that can cause disease in humans, and pathogen contamination is the primary cause of water quality impairments in the Great Lakes and nationwide.  Storm events stress urban infrastructure and increase pollution sources, particularly sewage overflows.  With predictions of increasing frequency and intensity of storm events in the Northeast and Great Lakes regions, climate change may hold negative consequences on pathogen burdens at beaches and in drinking water sources.  The impacts of climate change need to be quantified so priorities can be identified and adaptive strategies can be devised.

To investigate the influence of altered climate on urban infrastructure, we used downscaled climate projections that are representative of mid-21st conditions to assess changes in sewage overflows. The Milwaukee metropolitan area recently underwent extensive water quality planning in 2004-2006, including assessment of wastewater infrastructure and combined sewage overflows, but these assessments relied upon current climate conditions.  We utilized downscaled probability projections from global models to assess the increased stress on urban sewer infrastructure.  We assessed the changes in number of sewage overflows as the result of “best” and “worst” case climate scenarios.  Winter and spring rainfall is currently the largest determinant of sewage overflows because frozen or saturated ground offers limited storage capacity for runoff.  We found the number of combined sewage overflows increased by approximately 10% and the volume of sewage overflows increased by 20% under worse case conditions.  Importantly, the change in sewage overflows occurred during winter and spring. The combination of increased temperatures (changing snowfall to rainfall) and increased precipitation and/or intensity can act synergistically to impact urban areas during the seasons in which they are already most vulnerable to sewage overflows. These results are applicable for urban centers worldwide as development and changing climate patterns may exceed sanitation capacity.