Green Infrastructure in Series Reduces Thermal Impacts of Stormwater Runoff

Stream temperatures across the world are increasing due to changes in land use and climate, especially in urban areas. This leads to hydrologic urban heat islands, where higher water body temperatures can have negative consequences on ecological and human health. Green infrastructure is a potential solution to mitigate the temperature of urban runoff; however, it is unclear how green infrastructure systems, especially those connected in series, can be best utilized to reduce the impact of urban runoff on downstream temperatures. This study seeks to fill this gap by monitoring a green infrastructure system in Milwaukee, WI—a bioswale and permeable paver that both discharge into a second bioswale—to evaluate its temperature mitigation potential. Results indicate that for the bioswale and permeable pavers connected in parallel, the bioswale outperformed the permeable pavers in reducing event mean temperatures (2.8°C cooler). In addition, the bioswale that performed secondary treatment further reduced the average event mean temperature across all storms by 4.2°C from the permeable pavers and 2.4°C from the bioswale. This study demonstrates the effectiveness of a green infrastructure connected in series in reducing runoff temperatures, which is important for addressing a critical threat to environmental and human health.