A Critical Review of Nature-Based Systems (NbS) to Treat Stormwater in Response to Climate Change and Urbanization

Purpose of Review

Rapid urban development significantly contributes to the alterations in watershed hydrology by removing vegetation and soil, increasing imperviousness, and reducing natural infiltration capacity. It also generates more pollutants that deteriorate the stormwater quality. In addition, the escalation of the hydrological cycle due to climate change is expected to lead to more frequent intense rainfall. This extreme rainfall generates more stormwater runoff and releases more pollutants from the catchment, which can degrade downstream waterways. Therefore, it is crucial to assess the impact of urbanization and climate change on both the quality and quantity of stormwater to effectively mitigate their severe consequences. Nature-based solutions (NbS) for stormwater management are environmentally sustainable options to capture and treat pollutants from stormwater, reduce stormwater volume, and mitigate floods. However, significant modifications are needed in the existing nature-based treatment solutions to control floods and remove pollutants in rapid urban landscapes and extreme climate conditions. This review summarizes the current state of knowledge by (1) examining the potential impacts of urbanization and climate change on the stormwater quantity and quality; (2) assessing the performance of nature-based treatment systems to treat stormwater pollutants; (3) comparing the effectiveness among different nature-based treatment systems and identifying the best ones depending on the conditions; and (4) suggesting improvements to the design of wetlands to capture higher proportions of pollutants under different scenarios.

Recent Findings

A review of the literature indicates that densely built-up catchments produce increased runoff from impervious surfaces. In addition, industrial catchments generate higher total suspended solids (TSS) loads, while residential and commercial catchments generate more nutrients, such as nitrogen and phosphorous. Besides this, climate change is projected to increase annual runoff volume and mean annual concentrations of pollutants. For example, in Difficult Run watershed, the largest watershed in Fairfax County VA, an increase of 6.5% annual runoff volume and 7.6%, 7.1%, and 8.1% total suspended solids, nitrogen, and phosphorus mean annual concentrations, respectively, are expected for the simulated time period between 2041 and 2068. NbS such as swales, bioretention, detention ponds, and constructed wetlands have been implemented to remove the pollutants from stormwater, and constructed wetlands (CWs) have shown promising results in removing pollutants compared to other nature-based treatment systems. However, the efficiency of CWs can be improved by changing the filter media and vegetation and modifying the design to adapt to these adverse scenarios generated by rapid urbanization and climate change.

Summary

In the past, researchers have typically examined the impacts of rapid urbanization on stormwater quality, the influence of climate changes on stormwater quality, and the individual performances of various nature-based treatment systems (NbS). However, a comprehensive understanding of stormwater management necessitates exploring the dynamic interactions among multiple factors, including urbanization effects, climate change impacts, stormwater sources, and the effectiveness of NbS. This paper addresses this need by conducting a thorough review of all NbS utilized in stormwater management. The comparison encompasses their scales, performances in flood attenuation, provision of delay time for peak stormwater flow downstream, and the removal of pollutants from stormwater. Furthermore, a critical evaluation of NbS for stormwater management is presented, considering aspects such as urban ecosystem services and the climate-biodiversity-societal nexus. The insights provided in this research aim to inform decision-making processes related to the design, installation, operation, and maintenance of nature-based treatment systems in future stormwater management endeavours.