The water systems of the world - aquifers, lakes, rivers, large marine ecosystems, and open oceans - support the socioeconomic development and wellbeing of humanity and are home to a high proportion of the world’s biodiversity. Many of these systems are shared by two or more nations, and these transboundary resources are linked by a complex web of environmental, political, economic and security interdependencies. The interdependencies extend not only across national borders, but also between the different water systems, underlining the need for integrated management of these resources (see how these interlinkages are explored under the 'Indicators' section of this page).

While ecosystem services provided by these systems support the socioeconomic development and wellbeing of much of the world’s population, these basins continue to be impacted and degraded by multiple and complex human-induced and natural stresses. Further, management of transboundary waters is increasingly becoming constrained by limited availability of funds, resulting in the need for better prioritization of the allocations of limited financial resources. One of the major constraints to the effective management of transboundary waters is the lack of a systematic, periodic global comparative assessment of their changing conditions in response to changing stresses.
The Transboundary Waters Assessment Programme (TWAP) was initiated by the Global Environment Facility (GEF) to create the first baseline assessment of all the planet’s transboundary water resources. This serves a number of purposes, including benchmarking and knowledge exchange, identification and classification of water bodies at risk, and increased awareness of the importance and state of transboundary waters. It is hoped that the TWAP will be of use to a broad variety of stakeholders, including transboundary institutions for specific water systems (e.g. river basin organisations), national institutions and governments, as well as international agencies and donors, to obtain an overview of global issues threatening human populations and ecosystems through the water system. Thus, the long-term goal of the TWAP is to promote investment in management and development of transboundary water systems through strong stakeholder engagement.

The TWAP contains one component for each of the five water systems: (i) Groundwater, (ii) Lake Basins, (iii) River Basins, (iv) Large Marine Ecosystems (LMEs), and (v) Open Ocean. This website hosts the results of the assessment work of the TWAP River Basins component.

The TWAP River Basins (TWAP RB) component is a global assessment of 286 transboundary river basins, aimed at enabling the prioritisation of funds for basins at risk from a variety of issues, covering water quantity, water quality, ecosystems, governance and socio-economics. The TWAP RB assessment also covers risks to deltas from threats of a transboundary nature, and considers the relative influence of lakes on these river basins. TWAP RB is an indicator–based assessment, allowing for an analysis of basins, based on risks to both societies and ecosystems. It also includes provisional outlook projections to 2030 and 2050 for a limited number of indicators.

The methodology of TWAP RB builds on existing datasets and decades of assessment work. Importantly, it involves well-established partnerships between institutions that have a history of working together, as well as bringing in other institutions that add value and expertise and broaden the scope of the network. Formalizing these partnerships under the framework of the TWAP has created a sound basis for a sustainable process.

The Global Transboundary River Basins

The world’s transboundary river basins span 151 countries, include more than 2.8 billion people (around 42 % of the world’s population), cover 62 million km2 (42 % of the total land area of the Earth), and produce around 22 000 km3 of river discharge each year (roughly 54 % of the global river discharge).

The delineation of the 286 global transboundary river basins has been one of the key outputs of the TWAP RB component.  The TWAP RB component was able to improve existing account and delineations of the global transboundary river basins, thereby creating an update from the latest known list of 276 transboundary basins within the Transboundary Freshwater Dispute Database (TFDD) maintained by Oregon State University. 

From earlier known transboundary river basin delineations ( 214 transboundary basins identified by UNDESA (1978), 261 by Oregon State University (1999), 263 by OSU (2002), 276 by OSU (2012)) the number has thus risen to 286. The increase in number of transboundary river basins over the years have been a factor of improved global Digital Elevation Models (DEMs) and breaking up of countries. The latest basin delineations are based on HydroBASINS (Lehner and Grill 2013), which is an update of HydroSHEDS, using a 90m DEM. The global map of the 286 transboundary basins can be seen below and explored in further detail in the TWAP RB Data Portal. More information on methodology of the updated delineation can be found here.


The River Basins working group is made up of nine partners, with UNEP-DHI as the coordinator of the assessment.

combined logos

•    UNEP-DHI Partnership: Centre on Water and Environment (component coordinator). UNEP-DHI draws on more than three decades of experience in water resource management, policy and modelling and has been involved in a number of global, regional and local assessments for the UN and other bodies (e.g. UN-Water World Water Development Reports (WWDRs), UNEP Global Environment Outlooks (GEOs)). UNEP-DHI is familiar with GEF and UNEP processes and has a broad network including river basin organisations, private companies, research institutions and UN organisations, and is therefore well placed to coordinate the River Basins component. It is also responsible for the Wastewater Pollution and Enabling Environment indicators.

•    Stockholm International Water Institute (SIWI). Transboundary Water Management is one of SIWI’s main work areas and SIWI expertise in water governance and socioeconomic aspects of water is an essential component of TWAP. Within the TWAP RB, SIWI is responsible for the Legal Framework Indicator, the cross-cutting governance assessment, and supporting component coordination. SIWI also contributes to the sustainability aspects of the assessment.

•    International Union for the Conservation of Nature (IUCN). IUCN is a leading provider of biodiversity knowledge, and its products (e.g. Red List Index) have already contributed to valuable global assessments and reporting (e.g. Millennium Ecosystem Assessment, Convention on Biological Diversity (CBD) Aichi Targets). IUCN also has experience in defining ways to improve livelihoods and enhance human wellbeing while conserving the integrity and health of water ecosystems and their services. IUCN is responsible for supporting component coordination including harmonisation of the adopted basin delineation layer and review of reporting on ecosystem indicators, and the Extinction Risk indicator.

•    CUNY Environmental CrossRoads Initiative, City College of New York, is an internationally recognised centre for environmental research, and a unique meeting ground for science and policy experts. CUNY CrossRoads employs regional to global scale hydrology models (WBMplus) to assess how humans are embedded into the basic character of the water cycle through water abstraction and flow diversion, land-cover change, pollution, destruction of aquatic biodiversity, and climate change. Within TWAP RB, CUNY is responsible for the following indicators: Human Water Stress (current status and projected stress), Wetland Disconnectivity, Ecosystem Impacts from Dams, and Threat to Fish.

•    Centre for Environmental Systems Research (CESR), University of Kassel, with the WaterGAP (Water - Global Analysis and Prognosis) model, has broad experience in modelling and assessing global water resources, i.e. current and future water availability and sectoral water uses. CESR supports the TWAP by providing its latest datasets and modelling capability and is responsible for the following indicators: Environmental Water Stress (current status and projected stress), Agricultural Water Stress, and Lake Influence.

•    Oregon State University (OSU), Program in Water Conflict Management and Transformation (PWCMT). The PWCMT creates and hosts the largest online database on international freshwater treaties and has undertaken a large number of projects to analyse the performance of transboundary institutions under diverse stressors. It also serves as a training, resource and information hub for students, citizens, officials, and business leaders across the United States and internationally, facilitating dialogue on critical water issues across diverse values and perspectives. It is responsible for the indicator Risk of Potential Hydropolitical Tensions due to Basin Development in Absence of Adequate Institutional Capacity (current and projected).

•    International Geosphere-Biosphere Programme (IGBP). IGBP projects develop comprehensive science plans through a process of discussion and consultation with the global scientific community, involving hundreds of scientists from all continents. This ensures the development of truly international research frameworks and fosters international and interdisciplinary networks within national and regional research efforts. IGBP, with its Global Nutrient Export from WaterSheds 2 (Global NEWS 2), is responsible for the Nutrient Pollution (baseline and projected) Indicators.

•    Center for International Earth Science Information Network (CIESIN), Columbia University, works at the intersection of the social, natural, and information sciences, and specialises in on-line data and information management, spatial data integration and training, and interdisciplinary research related to human interactions in the environment. Within TWAP RB, CIESIN contributes significant experience and data with respect to global population datasets, and is responsible for the indicators for Economic Dependence on Water Resources, Societal Wellbeing, Exposure to Floods and Droughts, and projected Change in Population Density, as well as contributing the global population datasets for the whole of the TWAP.

•   Delta Alliance (primarily Alterra and Deltares, Netherlands) is an international knowledge-driven network organisation with the mission of improving the resilience of the world’s deltas. Under TWAP RB, DA is responsible for the Delta Vulnerability indicators for a selection of significant transboundary deltas, drawing on methodologies developed for projects previously realized by the DA.

Supporting partners:

The main tool for exploring results of TWAP RB assessment is the TWAP RB Data Portal.


Data and results may be viewed in a number of different ways and functionalities available include:
  • Indicator risk maps at basin level
  • Indicator risk maps at Basin Country Unit (BCU) level
  • Results sheets and metadata description sheets can be downloaded for each indicator.
  • River basin factsheets can also be downloaded for each basin. These contain the background information relevant to each basin, as well as an overview of the assessment results for all indicators in the basin.
The assessment results portray a complex picture - there are serious risks to a wide geographic and developmental spread of basins for all of these issues. There is no single issue which is the most important, and there are no basins with either ‘very low’ or ‘very high’ risk for the full range of issues. Thus, the issues (indicators) are presented both separately (Chapter 3 of final technical report) and together (chapter 4) in a series of separate but linked analyses which drill down into the results from a number of different perspectives.

The challenges faced by basins and deltas include a mixture of threats which can be mitigated to some degree, but also unique geophysical, climatic and socioeconomic parameters which set the bounds for applying management responses. Ultimately, successful outcomes will only be achieved with a mixture of political will, resources and adequate governance capacity at both national and transboundary scales.

See links to full assessment report and the Summary for Policy Makers in the Publications and Press section.
The work undertaken as part of the TWAP RB assessment has resulted in a number of outputs of potential use to a wide range of actors.

TWAP RB consortium partners are currently in discussion with a number of organisations (including UNECE, WWF, GRID-Arendal, WWAP, CI, basin organisations and others) to identify potential collaboration opportunities to make best use of the existing assessment results, and to further develop the assessment methodology to better suit the needs of various organisations and global, as well as local uses.

Further description of these collaboration opportunities are included in the Sustaining Mechanisms Report.

Publications and Press

TWAP RB Assessment Report: Status and Trends
The final technical report of the TWAP RB assessment (March 2016). Contains results and results maps for all assessment  indicators, as well as integrated analysis accross indicators. The technical report is accompanied by Summary for Policy Makers.


TWAP RB Technical Assessment Report:

Summary for Policy Makers:

Chapter downloads:

    Table of Contents (high-res 3.9MB) (low-res 1.1MB)
    Chapter 1: Introduction (high-res 5MB) (low-res 1.5MB)
    Chapter 2: Assessment approach and methods (high-res 3.1MB) (low-res 1.1MB)
    Chapter 3: Transboundary river basins Indicator assessment (high-res 97.2MB) (low-res 10.5MB)
    Chapter 4: Integrated indicator analysis (high-res 15MB) (low-res 3.6MB)
    Chapter 5: Water systems links (high-res 9MB) (low-res 1.4MB)
    Chapter 6: Conclusions (high-res 7.4MB) (low-res 1.2MB)
    Table of transboundary river basins and their countries (169KB)

TWAP in Press

- Al Jazeera interview with TWAP RB PM Paul Glennie

- IUCN Blog post "First Global Transboundary Rivers Assessment identifies urgent priorities for development and conservation"

- Journal Article: A Comparative Analysis of Water Governance, Water Management, and Environmental Performance in River Basins. Christian Knieper and Claudia Pahl-Wostl, Water Resources Management, March 2016, pp 1-17.

Click on the appropriate links to learn more about the TWAP Full Size project, the assessment results and the other components of the TWAP.

TWAP Full Size Project website: and Data Portal:
TWAP Groundwater:
TWAP Lakes and Reservoirs:
TWAP Large Marine Ecosystems:
TWAP Open Ocean:

For enquiries regarding TWAP RB please contact:
Paul Glennie, UNEP-DHI or Maija Bertule, UNEP-DHI.

Last update: 06.04.2016.