Editorial: Potential and limitations of Nature-based Solutions (NbS) to global water challenges

Throughout human history, the idea of Nature-based Solutions (NbS) and the recognition of ecosystems' critical role in addressing societal challenges have been ingrained. Yet, NbS terminology only entered common lexicon in the early 2000s (Ruangpan et al., 2020). Increasing levels of attention over the last decade have been directed toward NbS in policy fora and scientific literature, mostly in an attempt to address the underestimated potential of NbS in the context of the current climate crisis.

NbS are defined as actions that are based on the operation of natural processes and implemented to achieve more sustainable and resilient societies. For instance, NbS for managing water availability include natural wetlands and their restoration as well as improvements in soil moisture and groundwater recharge (WWAP, 2018). NbS are cost-effective by definition and provide benefits to both biodiversity and human wellbeing (UNEP, 2022). Therefore, the defining feature of NbS is not whether the deployed solution is de facto natural, but whether natural processes are being employed and managed proactively to achieve desired objectives. NbS can function by conserving or rehabilitating natural ecosystems and enhancing or recreating natural processes in altered or artificial ecosystems at micro- or macro-scales.

In the context of water resources management, NbS are often deployed to solve or overcome some of the major contemporary water management issues or challenges, such as water security and scarcity. Especially the role of NbS in attenuating the impacts of opposing hydrological extremes, namely droughts and (pluvial) floods, make NbS, due to their water retention capabilities in the landscape, a cornerstone in the water-storage-continuum concept (McCartney and Smakhtin, 2010). Nonetheless, NbS are also applied routinely in circumstances where no critical local water problem exists, for example, attenuation of pollutants in the subsurface producing the generally safe and high quality of abstracted groundwater for water supplies (WWAP, 2018).

A critical aspect of NbS implementation, and arguably of their success, is whether their use is technologically and institutionally supported and whether all stakeholders are engaged in NbS development and deployment, which is still viewed as a major challenge (WWAP, 2018; Ruangpan et al., 2020; UNEP, 2022). Contrasting perceptions and valuation of the co-benefits by stakeholders can lead to trade-offs and potential conflicts (Giordano et al., 2020), hampering the deployment of NbS. Moreover, the “negative externalities from ‘gray’ alternatives are often not accounted for” (UNEP, 2022), which requires more emphasis on demonstrating the effectiveness of NbS in achieving the envisaged objectives in design (Anderson et al., 2021).

The present Research Topic contributes to exploring both merits and limitations of implementing NbS to address water challenges in policy and decision-making, highlighting the potential of NbS to address water management challenges across various sectors. Four different studies shed light on different aspects of NbS for water, including different ways how NbS help to mitigate pluvial and riverine flooding as well as agricultural adaptation with respect to water use as a response to droughts (see Figure 1).

Figure 1. NbS types addressed by the four papers in this Research Topic. Two dimensions are considered. The left part considers measures for managing infiltration and surface runoff. In contrast, the right part compiles measures that alter flow paths, e.g., grassed waterways for retaining pluvial flooding and erosion (Fiener and Auerswald, 2017). The top row compiles measures at the landscape level, while the bottom line presents NbS for the urban space. Some measures (e.g., decentral retention is relevant in both cases). Figure inspired by WWAP (2018).

Among several measures, Pinos and Timbe (Paper 1) specifically address the term smart land management in order to mitigate riverine flooding in Peru. The idea of smart land management is here well in line with the concept of managing infiltration and flow paths in the landscape.

Wens et al. (Paper 2) explore agricultural adaptation decisions in response to drought risk. They employ a socio-hydrological agent-based model to analyze the way farmers adapt to drought risk under different assumptions. Adaptation measures include improving in-soil water storage using mulch cover (managing storage) and constructing terraces (managing infiltration, storage, and flow paths). Though their analyses also included measures like wells and drip irrigation, the relevance of the aforementioned NbS in agricultural adaptation is highlighted.

While the previous study mainly focuses on drought risk and adaptation of agricultural areas, Li et al. (Paper 3) demonstrates the results of a survey on the perception of flood risk in urban areas with an emphasis on the role of floodable areas in cities, which are foreseen to be temporally flooded. This concept is also suggested by van Hattum et al. (2016). The study highlights that most participants perceived flooded areas as less safe than classical retention ponds, highlighting the relevance of focusing on new strategies needed to increase the acceptance of NbS.

Finally, Wübbelmann et al. (Paper 4) quantify the effect of different NbS measures, including trees, green roofs and unsealing of paved areas in terms of flood-regulating ecosystem services. While the methodological framework is introduced by Wübbelmann et al. (2022), the current paper compares how NbS contribute to flood-regulating ecosystem services in urban areas under more extreme rainfall due to climate change. Even though the method demonstrates the limitations of NbS under extreme rainfall, it also highlights the role of an ecosystem services demand and supply budget approach to support planners and decision-makers.

Although only four studies with very different perspectives and analyses are compiled here, it can be said that they make an important contribution against the background of the challenges and opportunities outlined above. This holds especially true for the relevance of NbS as an efficient way to mitigate flooding in the landscape (Papers 1 and 4) and the question of how to increase the acceptance of these measures (Papers 2 and 3). The studies show, on the one hand, how decisions are made for the introduction of certain measures, including their effectiveness in economic terms (Paper 2) and on the other hand, also demonstrate the still not very pronounced openness toward certain measures (Paper 3). New concepts, including socio-hydrological modeling of NbS (Paper 2), extensive surveys on the effectiveness and perception of NbS (Paper 3) and new methodological approaches for planning purposes in an interdisciplinary context under the umbrella of ecosystems services (Paper 4) are promising approaches to feature the implementation of NbS in the future. Better interaction with people in NbS-related research is also envisioned in the new scientific decade of the International Association of Hydrological Sciences (IAHS), HELPING—Hydrology Engaging Local People IN one Global World.¹

Author contributions

FT: Conceptualization, Writing—original draft, Writing—review and editing. FA: Conceptualization, Writing—review and editing. SD: Conceptualization, Writing—review and editing. KF: Conceptualization, Visualization, Writing—original draft, Writing—review and editing.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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