Aquatic ecosystems are under increasing pressure from urbanisation, compounded by the escalating effects of climate change. With almost 60% of Europe’s water bodies considered to not be in a good ecological status and a global trend towards urbanisation, urgent efforts are needed to protect aquatic biodiversity.

One specific challenge relates to sewage overflow events, which are caused by heavy rainfall that overwhelm combined drainage systems (transporting wastewater, stormwater and urban runoff to sewage treatment plants). The high water volumes can flood these systems and result in contaminated runoff being discharged directly into rivers, streams or other nearby water bodies. This is particularly prevalent in cities with a high rate of impervious surfaces, which prevent rainwater infiltration and increase the likelihood of such events. There is thus an urgent need to identify new solutions for reducing this burden both on sewage systems and aquatic ecosystems.

In response, NICHES explores the potential of nature-based solutions (NBS) to alleviate pressure on the combined sewage system during high rainfall events while also providing wider societal and environmental benefits. Examples of relevant NBS include riverbank restoration, sustainable urban drainage systems, constructed urban wetlands, the regeneration of urban green belts, or bioretention ponds. In order to support a wider uptake of these solutions, NICHES will utilise five global cities to collaboratively create a robust evidence base on potential benefits and trade-offs and identify pathways towards sustainable, resilient and just urban transformation.