Uncertainty: Concepts and definitions

From a socio-relational perspective, uncertainty is defined as a lack of a unique and complete understanding of the system to be managed [2]. From this standpoint, three distinct types of uncertainty are identified: incomplete knowledge, unpredictability, and ambiguity. Incomplete knowledge refers to the lack of knowledge about the present or future state of the system and its functioning. Unpredictability refers to what we cannot know about a system due to its inherent complexity. Ambiguity is a distinct form of uncertainty that concerns not how much actors know, but the different ways they understand and frame an issue. It reflects the coexistence of diverse, sometimes conflicting knowledge frames, raising questions about what matters and how to respond [5]. All these three kinds of uncertainty are present simultaneously, influencing each other, where the impact of a particular uncertainty may be created or enlarged through the cascading effects of other uncertainties.

Identification of uncertainties in a mediterranean river basin

The Mijares River Basin, situated in the Spanish Mediterranean region, exemplifies the complex challenges arising from climate change, historical land-use and land-cover changes, environmental degradation, and socio-economic transformations [6]. Multiple scholars have advanced understandings of how these complex dynamics shape climate–land use feedbacks across scales [6]. Traditionally, summer storms accounted for a large portion of the region’s rainfall. However, recent decades have seen a marked decline in these events. In response, scholars have proposed revegetation strategies to help restore the water cycle and improve water retention throughout the basin by re-coupling its atmospheric and terrestrial components (e.g., [7]). Implementing such a strategy, however, is anything but straightforward. It is fraught with unknowns and unpredictability, both in terms of how to operationalize the intervention and whether it can effectively restore the water cycle [8].

Building on prior knowledge of the problem’s physical dynamics, land use mapping, and sustainable land management practices [9], we conducted a series of basin-wide dialogues with stakeholders to explore key perceived uncertainties surrounding revegetation. These conversations, combined with an in-depth review of the scientific literature, revealed that implementing such changes involves far more than simply altering land cover. Instead, the uncertainties highlighted a complex interplay between climate, water, forest, soil, and people, producing cascading and compounding effects that may ultimately challenge the effectiveness of these interventions (Fig 1).

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Fig 1. Illustration of different types of uncertainty associated with revegetation.

Types of uncertainty: K: Incomplete knowledge and unpredictability; A: Ambiguity.

https://doi.org/10.1371/journal.pclm.0000617.g001

While scientific uncertainties were mostly concerned with the tree species, density, and distribution, soil moisture capacity, local atmospheric dynamics, and water availability [8]; the stakeholders raised different concerns, focusing on responsibility, rights, expectations and the very possibility of continued existence in the area [10]. Their perspectives introduced ambiguities about whether they could survive in such changing conditions, whether there would be enough water to sustain their livelihoods as farmers, whether future generations could remain on the land, and whether their lives would be endangered by increasingly frequent wildfires and water shortages.

What the Mijares case teaches us

The case of the Mijares River Basin offers a rich and concrete illustration of complex socio-relational dynamics in Mediterranean regions. As this case demonstrates, uncertainty is not simply a knowledge gap about the effects of revegetation; it also stems from the diverse, conflicting interpretations and priorities that emerge when different actors are confronted with the possibility of rethinking the land use scenarios in the basin. Here, revegetation appears as a contested solution, perceived very differently by upstream and downstream land owners and practitioners, city dwellers, and scientists. It raises not only technical questions about whether such measures can help increase water retention in the basin, but also political and practical ones: Who will benefit from the water generated? Who will pursue land management and how? Who will do the work, and under which conditions? Will it increase the incidence of forest fires and with it the risk of nearby populations?

Considering revegetation as a potential intervention, brings to the surface deep-rooted issues such as historical land-use changes, rural and institutional abandonment, depopulation, environmental degradation, neglected water infrastructures, fire management challenges, and broader socio-economic and institutional transformations. These factors have shaped the basin’s current state and will influence its future trajectories. In this context, the effectiveness of revegetation will not depend solely on what is known or unknown, but on what is considered acceptable and reasonable by those who must implement it and live with its consequences. As such this case reminds us that deciding over whether or not to revegetate the basin, requires not just better data, but better conversations among social actors.

Conclusions and ways forward

In conclusion, reframing uncertainty through a social-relational lens offers important implications for climate adaptation and water governance in complex landscapes. It shifts the focus from simply addressing knowledge gaps to engaging with the political, institutional, and normative dimensions of decision-making. Uncertainty is not only a matter of incomplete data or predictive limitations; it also arises from ambiguity, where multiple, legitimate ways of knowing and interpreting problems coexist.

Under this rationale, knowledge used to guide decisions about water cannot be limited to what is considered certain or uncertain within science. It must also acknowledge that ways of knowing water systems are diverse, context-dependent, and often ambiguous [11]. In many real-world contexts, multiple groups of actors coexist, each with their own histories, priorities, and perspectives. These actors may disagree not just about what is happening or what should be done, but even about what counts as relevant knowledge [12]. Mainstream approaches to climate adaptation tend to side-line these political and social complexities, treating disagreement as a temporary barrier to consensus rather than a fundamental feature of collective decision-making.

This reframing of uncertainty also calls for a shift in how science informs policy. Rather than delivering definitive answers, science should support processes of deliberation, reflection, learning and collective sense-making [13,14]. Disagreement, in this context, is not a barrier to progress, but a sign of pluralism and an opportunity for more resilient and context-sensitive governance [15]. By recognizing and engaging with the relational nature of uncertainty, policymakers and researchers alike can contribute to more inclusive and adaptive responses to the complex challenges of water governance under climate change.

Acknowledgments

We would like to thank Ambika Markanday, Bosco Lliso and Sacha Poultier for their participation at various stages of this research. We also would like to acknowledge the late Millán Millán for his pioneering work on climate–land interactions in the Mediterranean region, which laid the groundwork for our case study and continues to inspire our efforts.