Towards Sustainability in Transboundary Water Resources: The Role of Inter-State Solidarity

Abstract

While cooperation regarding the management of transboundary water resources continues to improve in terms of the extent and intensity of inter-State engagement, watercourse States will increasingly need to employ flexible arrangements to facilitate the adaptive management of shared waters in response to the likely impacts of climate change. The legal challenges involved in crafting and applying such arrangements will require greater focus upon the community of interest understood to exist amongst co-basin States, and greater reliance upon the principle of solidarity underlying this concept. Though long a feature of international law, solidarity plays a particularly important role in the continuing development and functioning of international water law, and today offers a set of cooperative values to assist international water law in adapting to the looming global water crisis.

Introduction

It would scarcely be possible to overstate the extent of the social, economic and environmental risks presented by the looming global water crisis. ¹ A recent World Meteorological Organisation (WMO) report on global water resources highlights the very severe stress currently facing global water supplies, with five consecutive years of below-normal river flows and reservoir inflows seriously impacting communities, agriculture, and ecosystems. ² The report identifies a range of factors contributing to these problems, but human-induced climate change features prominently. The WMO notes, for example, that 2023 was the hottest year on record, with glaciers experiencing their largest annual loss of mass in the last 50 years, and 2023 marking the second year of widespread ice loss globally. As time goes on, climate change is certain to make the hydrological cycle and related river flows significantly more erratic. Already, 3.6 billion people currently face water shortages, with this figure projected to exceed 5 billion by 2050. It is clear, therefore, that international water law must evolve to provide decision-makers with a range of appropriate cooperative tools and solutions which are adequate to the task of addressing such challenges in shared international river basins, which account for 60 per cent of the world's freshwater flows. ³

On the contrary, however, it appears that the established patterns of transboundary water cooperation have crystallised around a suite of core rules and principles which predate the emerging water crisis and can increasingly be regarded as somewhat out-of-date and unfit-for-purpose. Most notably, the established rules of international water law, having largely emerged from the practice of interaction amongst watercourse States relating to the development of major water-related infrastructure projects in shared international basins, are chiefly concerned with ensuring stability as regards the regime applying to the water-related uses and entitlements of each State. Such stability has been essential in order to safeguard financial investments by ensuring the long-term viability of such infrastructure projects. The type of adaptive water governance now is required to assist States in responding flexibly to erratic river flows. The significant risks associated therewith for cooperative transboundary water resources management, is largely anathema to the objectives, commitments and procedures set out under existing transboundary water cooperation regimes. It is increasingly apparent, therefore, that many of the presumptions upon which the general framework of international water law is based, require urgent and fundamental reassessment.

In terms of the higher-order values and fundamental principles which underpin transboundary water cooperation along with rules of international water law (IWL), the looming water crisis demands an acceleration of the ongoing gradual transition from a short-term self-interested paradigm, based upon a narrow conception of State entitlements ensuing from territorial sovereignty, towards one based on the existence of a community of interest amongst States sharing such a uniquely vital natural resource. Though a State's right to pursue its sovereign interests in the use of a shared watercourse has long been qualified to some degree by the equitable requirement to take account of the reasonable interests of other watercourse States. ⁴ This established paradigm doesn’t necessarily support the optimisation of increasingly scarce water resources with a view to maximising human benefits and ensuring the resilience of water-related ecosystems. This transition, which, though clearly already underway, is becoming ever more urgent and mirrors Friedmann's prescient vision of international law's general evolution from a law of “coexistence” to a law of “cooperation”. ⁵

This article seeks to provide a snapshot of existing cooperative practice in the management of shared international water resources and, in so doing, to highlight the urgent need for flexible arrangements to facilitate the adaptive management of such waters in response to the likely impacts of climate change in terms of flow variability. It argues that such adaptive flexibility will require watercourse States to recognise the legal significance of the community of interest existing amongst co-basin States and to embrace the principle of solidarity which underlies and supports it. Solidarity has long been an important feature of international law, facilitating meaningful inter-State engagement and compromise, but it has played a particularly important, if under-explored, role in the evolution and functioning of modern international water law. Today, however, it offers a highly relevant set of cooperative values which can assist in ensuring that the practice of international water law can adapt to the looming global water crisis.

The Imperative of Transboundary Water Cooperation

The extent and intensity of inter-State cooperative engagement over shared transboundary water resources has been increasing steadily for some time. Several factors lie behind this increased interaction, including the impetus provided by the global commitment to transboundary water cooperation contained in Sustainable Development Goal (SDG) indicator 6.5.2, which is supported by a framework of related monitoring and reporting processes. The recently published third report on progress in the implementation of SDG 6.5.2 provides a useful snapshot of examples of cooperative arrangements that have been adopted or have entered into force between 2020 and 2023, and includes nine formal agreements, three memoranda of understanding, two protocols and two ministerial declarations. ⁶ While such increased inter-State interaction is to be welcomed as compelling evidence of heightened transboundary water cooperation - an absolutely indispensable element of improved transboundary water resources management - there are as yet few indications that such arrangements are specifically tailored to address the severe, yet novel and unprecedented, challenges presented by the increasingly likely impacts of climate change.

The key problem is one of treaty design. On the basis of the outline template provided by the International Law Association's seminally important 1966 Helsinki Rules, ⁷ and firmly established in the treaty practice of States by the 1997 UN Watercourses Convention ⁸ (and to a lesser degree the 1992 UNECE Water Convention, ⁹ which was originally regional in its geographical scope and primarily environmental in its substantive focus), international water resources agreements have tended to adopt a highly standardised format at the global, regional, river-basin and bilateral levels. Generally, in addition to institutional arrangements for facilitating their implementation, international water agreements tend to include the following key substantive and procedural elements: the principle of equitable and reasonable utilisation; ¹⁰ the duty to prevent significant transboundary harm; ¹¹ the general duty to cooperate; ¹² commitments regarding environmental and ecosystems protection; ¹³ a requirement of prior notification of planned projects; ¹⁴ requirements regarding routine exchange of data and information; ¹⁵ requirements regarding inter-State consultation and negotiation; ¹⁶ and arrangements for the settlement of disputes. ¹⁷ While improved transboundary water cooperation in the shape of newly adopted water agreements is undoubtedly necessary having regard to the looming challenges, the consistency in practice and normative stability promoted by this tendency towards highly standardised content and format lacks adaptive capacity and flexibility. Thus, though the format has evolved over more than six decades in response to the needs of diverse transboundary water cooperation scenarios and processes, it militates against the kind of continuing flexibility that climate-related water resources variability will require.

For example, the recent practice of international water law places great emphasis on the prior notification of contentious projects to potentially affected watercourse States, and on ensuing good-faith inter-State consultation and negotiation with a view to resolving any outstanding differences, ¹⁸ all of which is to be based on the findings of an environmental impact assessment (EIA) process conducted to international standards. In recent decades, many international water agreements have either required, ¹⁹ or promoted reliance upon, ²⁰ EIA procedures in order to facilitate meaningful and effective inter-State engagement concerning new projects. But, International Court of Justice (ICJ) now describes the conduct of an EIA in respect of a project likely to impact an international watercourse as a ‘requirement under general international law’, thereby suggesting that the obligation to conduct an EIA no longer depends upon an applicable treaty provision. ²¹ However, despite the obvious benefits of EIA in seeking to identify and prevent possible transboundary harm, it is in essence a onetime, ‘front-loaded’ process which assumes the possibility of predicting and mitigating adverse impacts in advance of the commencement of a project ²² – an assumption that is largely undermined by the uncertainty likely to beset water resources quantity and quality due to climate change.

Scholars have outlined the significant role(s) that established principles of international water law will be called upon to play, in both mitigating climate change and adapting to its water-related impacts. ²³ The formulation of inherently indeterminate and flexible cardinal principle of equitable and reasonable utilisation, as set out under the UN Watercourses Convention, requires watercourse States to have regard to ‘[g]eographic, hydrographic, hydrological, climatic, ecological and other factors of a natural character’ in any determination of States’ respective rights to use an international watercourse, ²⁴ alongside ‘[t]he population dependent on the watercourse in each watercourse State’ ²⁵ and ‘economy of use of the water resources of the watercourse and the costs of measures taken to that effect’, ²⁶ whilst also exhorting them to seek to attain ‘optimal and sustainable utilization thereof and benefits therefrom, taking into account the interests of the watercourse states concerned, consistent with adequate protection of the watercourse’. ²⁷ Clearly, this provides significant scope for addressing the challenges posed by climate change. ²⁸ Similarly, the general duty to take all appropriate measures to prevent significant harm to other watercourse States ²⁹ should operate to avoid or mitigate any adverse transboundary impacts of unilateral adaptation measures and ensure that the potential transboundary impacts of one State's use of shared waters are not further aggravated by climate change. ³⁰ In addition, the protections and entitlements arising under the emerging human right to water framework, ³¹ which inevitably informs the elaboration and application of rules of international water law by means of the field's traditional prioritisation of ‘the requirements of vital human needs’, ³² might prove helpful, ‘even though this right has not yet gained any appreciable traction in either international climate negotiations, mitigation policies or national adaptation plans’. ³³ Also, the environmental provisions routinely contained in international water agreements are also relevant in addressing climate change impacts, particularly in the case of the ecosystems obligations of watercourse States, ³⁴ which are increasingly associated with a requirement to maintain minimum environmental flows. ³⁵ However, as with most of the key established substantive and procedural principles of international water law, ‘[t]his principle needs to be implemented through joint institutional mechanisms where riparian states discuss and exchange data and information on the changing conditions of a river under the pressure of climate change.’ ³⁶ Significantly, the general duty to cooperate lies at the heart of the framework provided by international water law, ³⁷ and this provides the legal basis for the kind of intensive inter-State engagement which will be so essential in facilitating effective adaptation to climate change. Nevertheless, notwithstanding the considerable degree of flexibility permitted by the key principles of international water law, leading commentators tellingly caution that

‘there is the risk that the relatively static nature of IWL arrangements and the absence of clear joint climate change adaptation strategies hamper effective actions by riparian states. Thus, apart from applying the existing principles of IWL, it is necessary to negotiate, implement or revise transboundary freshwater agreements taking into consideration the uncertain nature of the impacts of climate change and developing joint mechanisms to address the impact of climate change on water resources.’ ³⁸

The Challenge of Adaptive Management

Having regard to the uncertain, yet potentially unprecedented, water-related threats presented by climate change, along with the continuing catastrophic decline of aquatic ecosystems and resulting loss of related ecosystem services, ³⁹ it becomes ever more apparent that shared international water resources require the development and adoption of effective adaptive management strategies. Such strategies tend to focus on resilience, with a view to conserving continually evolving, complex and resilient ecosystems, and are generally characterised as ‘iterative and flexible, responsive to the constantly changing conditions of both complex ecosystem processes and available scientific knowledge’ in seeking to ensure the “resilience” of an ecosystem. ⁴⁰ Adaptive management can address fundamental uncertainty regarding the functioning of complex dynamic socio-ecological systems by adopting a systemic approach for adapting and improving natural resources management by learning from previous policy and management interventions. ⁴¹ Clearly, ecological and hydrological uncertainty will be greatly exacerbated by the threat posed to freshwater ecosystems by climate variability, making the case for adaptive strategies ever stronger. ⁴² The legal basis for employing such strategies is quite straightforward, as they are understood to play a central role in effective application of a so-called “ecosystem approach”. ⁴³ The obligation to protect and maintain watercourse ecosystems is now firmly established as a central tenet of general international water law, ⁴⁴ with the State parties to one global water-related convention exhorted to include ‘the application of the ecosystems approach’ as an aspect of the measures to be adopted in promoting sustainable water resources management. ⁴⁵ Indeed, the requirement to employ an ecosystem approach may already enjoy autonomous legal authority, at least in the field of international watercourses law. ⁴⁶ Further, adaptive management is linked to the precautionary principle, as both seek to accommodate scientific uncertainty ⁴⁷ and the former can be regarded as a means of implementing the latter, ⁴⁸ which enjoys extensive support as established customary international law. ⁴⁹ In addition, one might regard consistent International Court of Justice (ICJ) endorsement of a requirement for “continuing” environmental assessment in disputes concerning transboundary watercourses as amounting to judicial recognition of the role of adaptive ecosystem-based management in certain situations of scientific uncertainty. ⁵⁰

The challenge that climate change presents for water resources management has long been understood, ⁵¹ as has that of introducing adaptive decision-making processes into water resources management frameworks, ⁵² and intergovernmental bodies have developed detailed practical guidance to assist international watercourse States in this regard. ⁵³ Most notably, the Task Force on Water and Climate, established under the auspices of the UNECE Water Convention, published seminal 2009 general guidance on water and climate adaptation ⁵⁴ and then subsequently developed, in collaboration with the International Network of Basin Organisations (INBO), 2015 guidance specifically focused on adaptation in transboundary basins. ⁵⁵ The UNECE/INBO guidance lists and, using case-studies, elaborates upon a total of 59 “lessons” to assist international watercourse States including, for example, on how to craft ‘adaptive legal frameworks’, how to ‘implement existing transboundary agreements in a flexible way’ and how to ‘design new transboundary agreements to be flexible’. ⁵⁶ This latter collaborative initiative has given rise to the Global Network of Basins Working on Climate Change, which facilitates the sharing of experience on an ongoing basis across a wide range of basins globally, including those located in the territory of non-parties to the UNECE Water Convention. ⁵⁷ Nevertheless, it remains readily apparent that significantly enhanced institutional cooperation amongst watercourse States will be required in order to agree and implement the adaptation measures necessary to build resilience to the water-related impacts of climate change and resulting uncertainty in water availability and quality. ⁵⁸

However, incorporation of adaptive measures into traditional treaty frameworks is highly problematic due to the traditional prioritisation of stability of applicable legal rules, especially where they are intended to facilitate large-scale infrastructure investment in an international watercourse and/or to resolve inter-State water resource disputes. It is an established truism that legal frameworks governing transboundary water resources ‘are not structured specifically to address the increased variability, uncertainty, and potentially irreversible changes posed by climate variability and change’. ⁵⁹ This feature is aptly illustrated by the well-established procedural rules of international water law, especially those concerned with inter-State notification and continued engagement over “planned measures”. More sophisticated legal arrangements are required, reflecting an adaptive approach which can accommodate uncertainty through flexible decision-making procedures which permit ‘incremental and gradual changes that transition experimentally to new standards or arrangements, while monitoring, assessing and adjusting these changes and their effects’. ⁶⁰ The established rules and principles of international water law are ‘based on historic conditions and linear patterns of change’, whereas ‘[t]he complex and uncertain dynamics of interconnected ecosystems and social systems … require that resource regulators and managers have a certain amount of discretion’. ⁶¹ It is clear, therefore, that robust and sophisticated joint institutional arrangements, enjoying broad mandates and adequate technical resources, are absolutely crucial to effective implementation of adaptive management. ⁶² River basin organisations (RBOs) and other cooperative institutional arrangements for transboundary water management rarely enjoy such freedom of action today, ⁶³ but the importance of their being empowered to react flexibly and decisively to changing conditions will become ever more apparent as the effects of climate change increasingly impact shared water resources. ⁶⁴ Such “common management” of shared international water resources, by means of appropriately empowered intergovernmental institutional arrangements, has long been associated with the persistent notion of a “community of interest” existing amongst the States sharing a particular international watercourse. ⁶⁵

Towards “Community” in International Water Law

The idea that States comprise, as the primary subjects of international law, an international “community” of interdependent actors has long been posited by scholars, ⁶⁶ though the precise legal implications of the existence of such a community remain unclear. ⁶⁷ At any rate, the specialist sub-field of international water law employs a particularly highly developed and pervasive notion of community interest amongst the riparian States in an international watercourse, giving rise to a general duty of institutionalised cooperation. ⁶⁸ This has long been recognised in the deliberations of international courts and tribunals; ⁶⁹ and is increasingly acknowledged explicitly in watercourse agreements, ⁷⁰ largely due to the immediately apparent interdependence of neighbouring States sharing a river basin. One can increasingly discern ‘manifestations of the culture of community and solidarity’ in the cooperative practice of watercourse States working within the framework of a successful basin agreement, such as the joint development and operation of large-scale water infrastructure on the Senegal river by the Organisation pour la Mise en Valeur du Fleuve Sénégal (OMVS). ⁷¹ Though in the past one might reasonably ‘doubt the possibility that the community of interest doctrine has entered the body of international customary law’, the sheer range, intensity and near-universal acceptance of cooperative activity at the international level regarding sustainable water resources management, exemplified today by the adoption of SDG Indicator 6.5.2 on transboundary water cooperation, alongside the reporting process jointly coordinated by UNECE and UNESCO, ⁷² suggests that the situation has evolved significantly. Leading commentators have long regarded to the notable convergence in State practice globally around institutionalised transboundary water cooperation as demonstrating ‘growing support for a community of interests approach to shared water resources management and development’. ⁷³ Indeed, the same authors describe international water law's modern ‘focus on building [institutional] legal regimes around the core substantive norms of equity and reasonableness’ as ‘hydrosolidarity in the making’, ⁷⁴ thereby highlighting the close interlinkage between the notion of solidarity and the community of interest approach, as both are based on interdependence and the need for collective action. ⁷⁵

Other developments within the practice of international water law suggest a growing sense of community in the relations amongst co-basin States. In particular, the emergence in human rights law, and its growing influence in international water law, the human rights to water paradigm, ⁷⁶ as epitomised in the CESCR's 2002 General Comment No. 15 ⁷⁷ and captured by the globally agreed ambitions set out under Sustainable Development Goal Targets 6.1 and 6.2, ⁷⁸ provides a stark demonstration of common interests arising amongst international watercourse States. Leading international law scholars tend to regard recognition of human rights in a particular sector as an indication of the emergence of community interest in that area of activity. ⁷⁹

More generally, it is the total human dependence upon water that gives rise to legal recognition of a community of interest among the States sharing a transboundary watercourse, and which similarly necessitates the deeply distributive conception of the notion of equity that pervades every aspect of international water law. ⁸⁰ This sense of community is further amplified by the fact that the circumstances pertaining in each international watercourse are quite unique, identifying transboundary water cooperation as an area of international legal activity particularly ‘likely to be influenced by regional postures and implications’. ⁸¹ The highly particularised requirements of each international watercourse regime can only enhance recognition amongst States of their interdependence and of the imperative of meaningful inter-State cooperation concerning shared water resources. The challenge presented by climate change can only render the common interests of watercourse States ever more starkly apparent.

The Critical Role of Solidarity

The intensification of interaction amongst watercourse States regarding their common interests, which inevitably gives rise to an increasingly highly developed sense of community, implies a certain measure of solidarity amongst the members of that community. ⁸² Solidarity enjoys a degree of recognition in the practice of States and international institutions, both in specialist fields, such as international disaster law ⁸³ or international climate law, ⁸⁴ and in general international law, ⁸⁵ prompting commentators to consider the existence and implications of a general “principle of solidarity” in international law. ⁸⁶ However, several key features of international water law demonstrate how values characteristic of this principle permeate every aspect of practice in the field, including the dominance and pervasive influence of distributive equity, the central importance of inter-State communication and cooperation, and the increasingly urgent imperative of optimising the human benefits to be derived from an increasingly scarce resource, whilst ensuring protection of vital aquatic ecosystems. ⁸⁷

As a ‘constitutive principle of social ties and equal rights’, ⁸⁸ solidarity is understood as a legal concept essential for any functioning community. It is closely associated with equality, fraternity, dignity, fundamental rights and individual and collective responsibility, all values which correspond with the ongoing shift away from the narrow and short-term self-interest traditionally pursued by sovereign actors. ⁸⁹ Solidarity has principally been associated with progressive and cosmopolitan human rights values, such as social welfare entitlements and migrant rights, and can thus lend itself quite easily to issues of environmental protection and sustainable natural resources management, including at the inter-State level. ⁹⁰ Solidarity therefore reflects the transboundary nature of many challenges in environmental and natural resources management and the reality of States’ interdependence, thereby implying the need for meaningful inter-State cooperation which would operate to counter narrow and short-term self-interest. ⁹¹

Solidarity has long been acknowledged, at least by scholars, as ‘both a fundamental and a fundamentally sound principle of international law’ and as ‘the basic condition for the existence of a community of states’. ⁹² Having regard to de Vattel's early characterisation of solidarity as a fundamental norm originating in natural law, and to its essential role in the functioning of international law and the maintenance of an international community of States, Macdonald suggests, in his seminal study of the origins and implications of the principle, that it comprises a peremptory jus cogens norm of international law, from which no derogation is permitted. ⁹³ This might however, be an overstatement of the principle's formal status in law. ⁹⁴ Other commentators suggest that solidarity may comprise, or may eventually evolve into, an obligation erga omnes, applying to relations amongst all States. ⁹⁵ Another speculates that, in certain circumstances, solidarity may transform key rules of international law into generally applicable erga omnes obligations, as ‘acknowledgement of common interests can promote solidarity, and solidarity is necessary for the protection of common interests’. ⁹⁶ Gjørtz Howden suggests, in her comprehensive study of the legal nature and implications of the community of interest approach in international water law, that this is certainly the case with transboundary water resources, where solidarity is ‘a central feature of erga omnes obligations in the sense that every [watercourse] State is considered to have a legal interest in their protection’. ⁹⁷ Though solidarity benefits from few express endorsements in formal legal instruments, ⁹⁸ the concept nevertheless penetrates the field of international environmental and natural resources law, including the specialist sub-field of international water law, by means of the central role ascribed to the overarching objective of sustainable development and the closely related concept of equity. ⁹⁹

One of the key dimensions of equity permeating the vision of sustainable development set out under the 1992 Rio Declaration is that of intra-generational equity, in the particular form of the principle of “common but differentiated responsibility” (CBDR) as between States bearing different degrees of responsibility for environmental degradation and possessing different national capacity to contribute to solutions. ¹⁰⁰ Solidarity informs every aspect of such differentiation as ‘’[t]he measure of common responsibility in the CBDR principle is thus rooted in the principle of cooperation, which posits that states are obliged, in the spirit of solidarity, to cooperate in preventing transboundary pollution’. ¹⁰¹ The universally accepted CBDR principle, which lies at the very heart of international environmental and natural resources law, and most notably the global climate and biodiversity regimes, is intended to promote inclusive sustainable development by ensuring flexibility in international environmental and natural resources cooperation having regard to three key factors, i.e., the extent of the needs, capability and responsibility of each State concerned. ¹⁰² Consistent with the central tenets of the concept of solidarity, a distributive conception of equity, such as that employed in international water law, ¹⁰³ involves the distribution of benefits derived from scarce shared resources primarily on the basis of the essential needs and capacity of each party. ¹⁰⁴ Thus the CBDR principle, and thereby the broader solidarity concept, is centrally relevant in international water law's response to the challenge of climate change.

The other equitable principle comprising a core element of the overarching objective of sustainable development, that of “inter-generational equity” which essentially requires the fair distribution as between present and future generations of the benefits to be derived from natural resources use, also implies a significant role for solidarity. Rio Principle 3 states that ‘[t]he right to development must be fulfilled so as to equitably meet developmental and environmental needs of present and future generations’, ¹⁰⁵ and is generally understood to mean that ‘each generation has an obligation to pass on the natural and cultural resources of the planet in no worse condition than received and to provide reasonable access to the legacy to the present generation’. ¹⁰⁶ This implies the existence of an inter-generational community and the relevance of solidarity between present and future generations in ensuring equitable balancing of the interests of each. The principle has received consistent support in declarative instruments since Stockholm, ¹⁰⁷ as well as more imperative expression in the preambular and textual provisions of a wide range of environmental and natural resources conventions, including some concerned with shared international water resources. ¹⁰⁸ It finds particularly cogent expression in the 1992 UNECE Water Convention ¹⁰⁹ and, though its precise normative status and binding force remains somewhat unclear, ¹¹⁰ the Brundtland Commission's Expert Group on Environmental Law could conclude in 1987 that ‘to the extent that this basic obligation concerns international or transboundary natural resources or environmental interferences, it already may in many respects be deemed to find substantial support in existing general international law’. ¹¹¹ Once again, this equitable principle, informed by the solidarity values underlying a sense of community, has a critically important role to play in addressing the water-related challenges of climate change.

Commentators increasingly recognise that key axiological elements of solidarity are intrinsic to effective transboundary water cooperation and are thus woven throughout the very fabric of the established rules and principles of international water law. ¹¹² This reflects international water law's instinctive pursuit of the increasingly urgent imperative of cooperative management of shared international freshwater resources with a view to optimising the welfare benefits derived from an increasingly scarce and environmentally vulnerable resource, thereby requiring (or at least encouraging) co-basin States to engage in intensive cooperative efforts, usually by means of permanent institutional mechanisms, involving difficult compromise on the part of all States. ¹¹³ In this way the principle of solidarity can operate as a counterweight to the contested absolutist conceptions of territorial sovereignty or integrity, upon which the interests of co-basin States recognised under international water law had traditionally been asserted and contested. Throughout the historical development of international water law, such sovereignty-based assertions of States’ respective rights and interests have operated to retard meaningful inter-State water cooperation by failing effectively to address tensions arising between upstream and downstream watercourse States and between more and less economically, socially or technologically developed watercourse States. ¹¹⁴ The adoption of such positions has largely encouraged States in contrasting geographical, hydrological or socio-economic circumstances to assert their narrow and short-term self-interest, rather than seeking mutually beneficial optimal outcomes.

Guided by the overarching concept of sustainable development, modern practice in relation to transboundary water resources is more likely to stress the interdependence of the community of co-basin States and the need for compromise in order to optimise human livelihood interests and effective ecological protection. Such aims require robust institutions to facilitate effective exchange of information and broad stakeholder participation with a view to identifying common goals and making difficult compromises socially acceptable. ¹¹⁵ In recent decades, the practice of international water cooperation has generally been characterised by the development of basin-level agreements and of supplemental guidelines and procedures for cooperative engagement under the auspices of institutional arrangements established thereunder. ¹¹⁶ By means of such cooperative institutional machinery, which is specifically designed to assist in finding compromise by making use of extensive cross-sectoral information and broad stakeholder participation, solidarity can operate to restrain unilateral action and to promote inter-State compromise based on sophisticated benefit-sharing arrangements which respect the hydro-climatic and socio-ecological limits of a shared basin. ¹¹⁷ Thus, the utility of the concept of solidarity is clear, as a broad value-framework and pervasive organising principle to inform and guide inter-State cooperation for the purposes of climate adaptation in shared international watercourses.

Conclusion

Whereas sociological thinkers ‘conceived of solidarity as the social glue that stimulates individuals to share with, and collaborate in, a larger collective’, ¹¹⁸ it has clear relevance and utility in the modern practice of international water law as ‘an understanding among formal equals that they will refrain from actions that would significantly interfere with the realisation and maintenance of common goals or interests’. ¹¹⁹ In this context, solidarity can be understood as a principle of modern international law, which is ‘beginning to inform the entire system … similar to the concept of equity …’. ¹²⁰ As a principle founded upon recognition of the formal equality and essential interdependence of the community of States, and the need for meaningful cooperation amongst States in order to maximise welfare, the solidarity has clear relevance for the progressive elaboration and practice of international water law in order respond to climate variability, where a commitment to solidarity can act as a counterweight to short-term and narrowly self-interested conceptions of the rights of States flowing from territorial sovereignty. ¹²¹