From classical water-ecosystem theories to nature-based solutions - Contextualizing nature-based solutions for sustainable city.

Growing interest in the concept of nature-based solutions (NBS) raises the question of its applicability as a broadly-understood approach to resource management and spatial planning. Although both the European Commission and United Nations consider the use of NBS as a vehicle to achieve numerous sustainability goals, the concept itself remains under-defined. We analyse the NBS concept against the background of classical water-ecosystem theories. We also review a range of potential contributions by NBS to various aspects of city management, resilience and adaptation. Finally we introduce the concept of a continuum of ecosystem service transfer across city management zones, with NBS acting as the medium, minimizing the net loss of regulatory services, and optimizing the cost-efficiency of solutions. We summarize with analysis of existing best practices in urban water management from the perspective of utilizing natural processes according to the supply and demand of services, and with a threefold target: enabling, restoring or preserving nature.