TWINBASINXN: Promoting Twinning of River Basins for Developing Integrated Water Resources Management Practices


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Summary of Findings

The 1978 Register listed 214 international basins, covering 47% of the world’s land surface (excluding Antarctica) (12). Our update lists 261 international basins, covering 45.3%, broken down by continent as seen in Table 1. The net addition of 47 international basins as compared to the 1978 Register comes about for three reasons: 1) National basins were internationalized through political changes, such as the break up of the Soviet Union and the Balkan states; 2) We were able to “find” several new international basins, due to better access to both digital and hardcopy maps; and, 3) The 1978 Register did not include many island nations. Because of these factors, we added a total of 51 new basins, as follows:

    Africa: Lotagipi Swamp, Mbe, Oued Bon Naima, and Umba.

    Asia: An Nahr Al Kabir, Astara Chay, Bangau, Beilun, Fenney, Har Us Nur, Kowl-E-Namaksar, Nahr El Kebir, Oral (Ural), Pandaruan, Pu-Lun-To, Sembakung, Song Vam Co Dong, and Wadi Al Izziyah.

    Europe: Barta, Castletown, Daugava, Dnieper, Dniester, Don, Elancik, Flurry, Gauja, Kogilnik, Krka, Kura-Araks, Lielupe, Mius, Narva, Parnu, Prohladnaja, Salaca, Samur, Sarata, Seine, Sulak, Terek, Venta, and Volga.

    North America: Alesek, Chilkat, Chiriqui, Firth, Taku, and Whiting.

    South America: Aviles, and Comau.

In contrast, four basins listed in the 1978 Register are no longer international, two due to the unification of Yemen (Tiban) and of Germany (Weser), and two due to our more consistent definition of “international basins.” The four “lost” basins are:

    Asia: Tiban

    Europe: Meuse, Muga, and Weser

Table 1: Number of International Basins

Continent 1999 Update 1978 Register
Africa 60 57
Asia 53 40
Europe 71 48
North America 39 33
South America 38 36
Total 261 214

Because our methods allow for a more careful delineation of basins than the 1978 Register, in some cases we were able to update the riparian nations which share international basins, along with updating the total number.These riparian relations are generally minor – often the contribution to the basin is more topographical than hydrological – and occasionally surprising.Such additions include Egypt on the Jordan, Saudi Arabia on the Tigris-Euphrates, and Libya on the Lake Chad system.While Botswana is listed as riparian to the Orange both in the 1978 Register and here, according to Conley and van Niekerk (1998) it is unclear whether Botswana territory actually contributes any water to the system and, as such, its political status as an Orange riparian remains to be clarified.

Focusing on the number of international basins masks another important dimension to the issue of international waters: the flow generated within these basins.Shiklomanov (1993) lists the flows of 25 of the world’s largest rivers, which total 19,200 km3, or a little less than half of the world’s total runoff.Of the total flow in these 25 rivers, 16,700 km3, or 87%, is generated within the 20 of these which are international.

In addition to the number of international basins and their riparian nations, a striking aspect of international waters is the percentage of the land surface of the earth which is included within their basins: 45.3%, excluding Antarctica (see Table 5: Percentage of a Country’s Area Within International Basins). By continent, this ranges from 62% of Africa to 35% of North America, as follows:

Table 2: Percentage of area within international basins

Continent 1999 Update 1978 Register
Africa 62% 60%
Asia 39% 65%
Europe 54% 50%
North America 35% 40%
South America 60% 60%
Total (excl. Antarctica) 45.3% 47%

Even more striking is a breakdown of each nation’s land surface, as provided in detail as Table 5.A total of 145 nations include territory within international basins.Twenty-one nations lie in their entirety within international basins; including these, a total of 33 countries have greater than 95% of their territory within these basins.These nations are not limited to smaller countries, such as Liechtenstein and Andorra, but include such sizable countries as Hungary, Bangladesh, Byelarus, and Zambia.All told, percentages of nations within international basins are as listed in Table 3.

Table 3: Percentage of nations within international basins

Percentage within
international basins
Number of countries
90-100% 39
80-90% 11
70-80% 14
60-70% 11
50-60% 17
40-50% 10
30-40% 10
20-30% 13
10-20% 9
0.01%-10% 11

A final way to visualize the dilemmas posed by international water resources is to look at the number of countries which share each international basin (see Map 8 and Table 6: Number of Countries that Share a Basin).Nineteen basins are shared by five or more riparian countries: one basin – the Danube, has 17 riparian nations; five basins – the Congo, Niger, Nile, Rhine and Zambezi – are shared by between nine and 11 countries; and the remaining 13 basins – the Amazon, Ganges-Brahmaputra-Meghna, Lake Chad, Tarim, Aral Sea, Jordan, Kura-Araks, Mekong, Tigris-Euphrates, Volga, La Plata, Neman, and Vistula (Wista) – have between five and eight riparian countries.


When water resources cross international boundaries, the challenges to integrated watershed management are compounded; the obstacles to political cooperation exacerbated.While interest in international river basins is growing along with global populations and economies, much in the way of basic data collection on these systems as a class remains to be done.We recognize too that this register is limited; that political boundaries will continue to shift, and that the technology of watershed analysis will continue to improve.The resolution of digital mapping data will continue to increase and the algorithms used to analyze them will become more robust.In the meantime, it is to be hoped that this updated register of the world’s 261 international river basins, covering 45.3% of the land surface of the earth, will contribute to continued analysis of these basins and perhaps, through greater understanding, tendencies towards cross-boundary cooperation might even be strengthened.


This work was performed under the auspices of the Committee for International Collaboration of the International Water Resources Association, chaired by Asit K. Biswas, with funding from the US Institute of Peace and the Nippon Foundation, and is a component of the Transboundary Freshwater Dispute Database Project, directed by Aaron T. Wolf. The authors are especially indebted to Prof. Biswas and to these agencies, as well as to those which helped fund different aspects of the Database, including the US Agency for International Development, Pacific Northwest National Laboratory, the Alabama Water Resources Institute, the University of Alabama, and Oregon State University.Jeffrey Danielson’s work was performed under U.S. Geological Survey contract #1434-CR-97-CN-40274, for which we are grateful. We owe special thanks to Tom Kallsen, director of the map library at the University of Alabama, who helped us find everything from satellite photos to topographic map sheets of the most obscure reaches of the world, and to Ashbindu Singh, of the United Nations Environment Programme, without whose close collaboration this project would not have been possible.We are also grateful to Shira Yoffe, of Oregon State University, for her research skills and political insight; to Peter H. Gleick, of the Pacific Institute, for his close reading and advice; and to Martin Pratt and the staff of the International Boundaries Research Unit at Durham University, for their expedited assistance with boundary ambiguities.Finally, thanks to A. Jon Kimerling, of Oregon State University, for his cartographic expertise; to Sandra Postel, of the Global Water Policy Project, for a particularly helpful discussion about the world’s irrigation; and to Jeff Albert, of Yale University, who provided the extra detail necessary to do justice to the Jordan River system.