Nat4Wat: a co-developed decision-support system for resilient urban water management with nature-based solutions

Nature-based solutions (NBS) have emerged as sustainable approaches to urban water management, addressing critical challenges like wastewater treatment and stormwater management while delivering additional environmental and social benefits. A significant advantage of NBS is their potential to decentralize urban water management, enabling cities to distribute water treatment and storage systems across multiple locations, thereby alleviating pressure on traditional centralized infrastructure. However, the wide array of NBS options, each tailored to specific contexts, presents a considerable challenge for decision-makers. The Nat4Wat decision-support system (DSS) was developed to help stakeholders select, compare, and evaluate NBS options for wastewater treatment and stormwater management. Nat4Wat streamlines decision-making by integrating a transparent multicriteria evaluation with an open knowledge base that links performance, costs, and cobenefits. By integrating multicriteria decision analysis (MCDA), Nat4Wat evaluates factors —such as cost-effectiveness, environmental performance, operational requirements, and social benefits— guiding users toward the most suitable and sustainable NBS for their specific needs. This paper details the co-development of Nat4Wat, in collaboration with technology providers and decision-makers, showcasing its application in two case studies: wastewater reuse at a rural hotel and stormwater mitigation in an urban area. These examples demonstrate how the tool streamlines decision-making, enhances transparency, and fosters stakeholder participation. As urban areas face increasing water-related challenges driven by climate change and population growth, Nat4Wat serves as a relevant resource for integrating NBS into resilient and sustainable urban water management strategies.