Water resources located in more than one country are complex systems governed by customary international law embodied in a rule known as equitable and reasonable utilisation, a recent development in international law not yet been applied by an international tribunal to resolve a dispute or to allocate transboundary water resources between countries. Water scarcity on a global scale has reached critical proportions with 1.1 billion people without access to sufficient safe water for personal and domestic use; over half that number depend on transboundary watercourses that will disappear over the next century. Conflicts of use over shared water resource have the potential to escalate into armed conflict; certainty in the peaceful means to avoid and resolve disputes is needed. The thesis examines international procedural practice and jurisprudence applying equitable principles in a case study to illustrate how equitable and reasonable utilisation may be applied by an international tribunal. The survey of international practice will inform States about procedural options for dispute avoidance and resolution in disputes over the use of transboundary water resources.

A Lei n° 9.433/1997 que institui a Política Nacional de Recursos Hídricos (PNRH) congrega as principais diretrizes de planejamento do uso da água a partir da incorporação de importantes Princípios como o do gerenciamento integrado dos recursos hídricos, gestão participativa, integralidade da bacia hidrográfica como interconexão de sistemas de águas superficiais e subterrâneas para gestão interna, resolução pacífica de conflitos, dentre outros. No contexto transfronteiriço, os contornos da cooperação podem ser tanto um instrumento facilitador como complicador das políticas hídricas a serem executadas, uma vez que à luz do Direito Internacional, as intervenções no território de um Estado devem seguir os Princípios da não intervenção, independência e soberania o que demanda uma política de coordenação internacional entre eles. Para estabelecer os contornos internacionais a respeito do que se pretende acerca de recursos naturais transfronteiriços, é usual o surgimento de regimes específicos, com tratado próprio, muitas vezes excetuado do regramento geral internacional. A fim de analisar o quadro jurídico aplicável no contexto hídrico transfronteiriço amazônico a presente tese parte do ordenamento jurídico brasileiro em matéria de gerenciamento de recursos hídricos e aplica, a partir da dimensão internacional, três esferas de análise dos Princípios da troca de informações e estudos prospectivos, solução pacífica dos conflitos, e da participação pública, nas seguintes perspectivas: 1. multilateral, no âmbito da OTCA; 2. bilateral/trilateral, na formação de instâncias ad hoc para a solução de conflitos; 3. local, na formação de Comitês de bacia internacional. / The Brazilian statute n. 9.433/1997 institutes the National Policy of Water Courses, which contains the most important parameters to set policies in this regard and is widely based on international principles, such as the principles of the integrated management of transboundary basins, integrality of the basins, interconnection between ground and surface water, as well as the peaceful settlement of disputes. Transboundary situations may foster or obtrude cooperation to set and execute water policies, since, accordingly to the international law, a state are not allowed to intervene in the territory of other states, because they are independent and sovereign. The only way to harmonize policies is international cooperation. In order to establish the international limits to the use of natural transboundary resources some international regimes usually arouse and are, sometimes, established by treaties which differ from general international law. Aiming to analyze the legal framework applicable to the Amazon transboundary waters, this thesis starts with a study of the Brazilian legal system regarding water resources management and employs, departing from an international perspective, three levels of analysis of principles that refer to exchange of information, prospective studies, peaceful settlement of disputes, and public participation, from the following perspectives: 1. multilateral, under the ACTO regime 2. Bi- and trilateral, when ad hoc instances are created to settle the disputes 3. Local, through the creation of International Basin Committees

A Lei n° 9.433/1997 que institui a Política Nacional de Recursos Hídricos (PNRH) congrega as principais diretrizes de planejamento do uso da água a partir da incorporação de importantes Princípios como o do gerenciamento integrado dos recursos hídricos, gestão participativa, integralidade da bacia hidrográfica como interconexão de sistemas de águas superficiais e subterrâneas para gestão interna, resolução pacífica de conflitos, dentre outros. No contexto transfronteiriço, os contornos da cooperação podem ser tanto um instrumento facilitador como complicador das políticas hídricas a serem executadas, uma vez que à luz do Direito Internacional, as intervenções no território de um Estado devem seguir os Princípios da não intervenção, independência e soberania o que demanda uma política de coordenação internacional entre eles. Para estabelecer os contornos internacionais a respeito do que se pretende acerca de recursos naturais transfronteiriços, é usual o surgimento de regimes específicos, com tratado próprio, muitas vezes excetuado do regramento geral internacional. A fim de analisar o quadro jurídico aplicável no contexto hídrico transfronteiriço amazônico a presente tese parte do ordenamento jurídico brasileiro em matéria de gerenciamento de recursos hídricos e aplica, a partir da dimensão internacional, três esferas de análise dos Princípios da troca de informações e estudos prospectivos, solução pacífica dos conflitos, e da participação pública, nas seguintes perspectivas: 1. multilateral, no âmbito da OTCA; 2. bilateral/trilateral, na formação de instâncias ad hoc para a solução de conflitos; 3. local, na formação de Comitês de bacia internacional. / The Brazilian statute n. 9.433/1997 institutes the National Policy of Water Courses, which contains the most important parameters to set policies in this regard and is widely based on international principles, such as the principles of the integrated management of transboundary basins, integrality of the basins, interconnection between ground and surface water, as well as the peaceful settlement of disputes. Transboundary situations may foster or obtrude cooperation to set and execute water policies, since, accordingly to the international law, a state are not allowed to intervene in the territory of other states, because they are independent and sovereign. The only way to harmonize policies is international cooperation. In order to establish the international limits to the use of natural transboundary resources some international regimes usually arouse and are, sometimes, established by treaties which differ from general international law. Aiming to analyze the legal framework applicable to the Amazon transboundary waters, this thesis starts with a study of the Brazilian legal system regarding water resources management and employs, departing from an international perspective, three levels of analysis of principles that refer to exchange of information, prospective studies, peaceful settlement of disputes, and public participation, from the following perspectives: 1. multilateral, under the ACTO regime 2. Bi- and trilateral, when ad hoc instances are created to settle the disputes 3. Local, through the creation of International Basin Committees

Achieving global water sustainability through a resilient international legal architecture presents one of the most pressing challenges within our resource finite planet. A staggering 42 percent of the total land area of the earth is covered by transboundary river basins, where more than 40 percent of the global population lives and depends on the ecosystem services of the 286 transboundary river basins and 200 transboundary aquifers stretching across the political boundaries of 151 countries. There is already evidence of water resources becoming a source of conflict in many regions and constraining a whole myriad of securities – climate, human, environmental, food, economic, energy – on various levels of society. The international legal architecture to manage this critical natural resource is the overarching area of inquiry in this thesis, and requires improvement to address current and predicted future transboundary water challenges, conflicts and strengthen cooperation. Despite the establishment of around 690 river basin treaties, many of these agreements completely miss or provide unclear provisions on principles and rules of international water law. Until recently there was no legally binding global treaty on transboundary watercourses and customary international law has provided the default rules in the absence of agreements and facilitated the re-interpretation of older agreements in accordance with the Vienna Convention on the Law of Treaties. Now there are potentially two global treaties, with the recent entry into force of the 1997 UN Watercourses Convention and the global opening up of the 1992 pan-regional United Nations Economic Commission for Europe (UNECE) Water Convention, to all UN member states. There is also a plethora of other international environmental legal and non-legally binding instruments, indirectly addressing international law relevant to transboundary watercourses and freshwater ecosystems. Legal regimes for the protection and use of international river basins cannot be interpreted and applied in isolation from other relevant norms of international environmental and general international law. This thesis seeks to understand the rising role and contribution of regional approaches relevant to international law on transboundary watercourses and freshwater ecosystems. More specifically it explores the contribution of the UNECE Water Convention and other relevant UNECE environmental instruments as a structurally distinctive ‘regime’. This thesis introduces a novel conception of a broader ‘UNECE water regime’ which includes the Water Convention, the Convention on Access to Information, Public Participation in Decision-making and Access to Justice (Aarhus Convention), the Convention on Transboundary Environmental Impact Assessment (Espoo Convention), the Convention on the Transboundary Effects of Industrial Accidents, as well as their protocols and non-binding instruments. This research demonstrates how these instruments and their institutions can be interpreted and understood to form a common framework of rules, principles and approaches which fills critical gaps in basin treaties, and collectively contributes to the clarification and development of international law on transboundary watercourses and freshwater ecosystems. This analysis also explores institutional interaction and coordination between and beyond the UNECE pan-regional agreements, as well as the role of soft law or non-binding instruments, and state and non-state actors in the regime. This thesis seeks to contribute to a more coherent understanding of the relationship between the UNECE water regime, international water law, international environmental law and general international law. The UNECE water regime has contributed to clarifying many of the cornerstone rules and principles of international water law and it is argued that the UNECE water regime is lex specialis, which can and mostly does go beyond the UN Watercourses Convention. The UNECE water regime has also arguably spearheaded a paradigm shift in international water law, which sees it moving beyond its historically predominant focus on issues of transboundary impact and utilisation towards a stronger ecosystem orientated approach to environmental protection and equitable use of transboundary river basins. This research identifies key elements of an ecosystem approach, drawing from international environmental and international water law and demonstrates how the ecosystem approach, including ecosystem services, as supported by the UNECE water regime, affects interpretation of international water law towards enhancing ecosystem protection and intra-state equity. This research also explores how the UNECE regime goes beyond what exists elsewhere in international law and international water law on public participation and access to justice. Finally, this research examines the contribution of the UNECE regime vis-à-vis international and European Union water law, across the spectrum of pan-European river basins, especially focusing on the Danube, Sava and Western Bug basins. The UNECE water regime is the most evolved pan-regional regime of its kind, providing ambitious detailed standards and clarification of rules and principles relevant to transboundary watercourses and freshwater ecosystems. It also provides a valuable model of institutional cooperation, progressively engaging state and non-state actors. As this regime takes steps towards realising its global ambition, with almost all instruments now open to all UN member states, and the recent accession by Chad to the Water Convention, this analysis demonstrates why this is predominantly a positive endeavour but also highlights potential challenges and hurdles. This research thus explores the implications and benefits of the UNECE’s rising role in strengthening the international legal architecture to protect the world’s fragile transboundary watercourses and freshwater ecosystems.