International Journal of Water Resources Development, Vol. 15 No. 4, December 1999.
Aaron T. Wolf
Table of contents
Abstract | Introduction | Methodology | Updating the river basins
Updating the political boundaries | Summary of findings
Table 1: Number of international river basins
Table 2: Percentage of area withing international basins
Table 3: Percentage of nations within international basins
Conclusions | Acknowlegdements
It is becoming acknowledged that water is likely to be the most pressing environmental concern of the next century.Difficulties in river basin management are only exacerbated when the resource crosses international boundaries.One critical aid in the assessment of international waters has been the Register of International Rivers – a compendium which listed 214 international waterways that cover 47% of the earth's continental land-surface.The Register, though, was last updated in 1978 by the now-defunct United Nations Department of Economic and Social Affairs.
The purpose of this paper is to update the Register in order to reflect the quantum changes that have taken place over the last 22 years, both in global geopolitics and in map coverage and technology. By accessing digital elevation models at spatial resolutions of 30 arc seconds, corroborating at a unified global map coverage of at least 1:1,000,000, and superimposing the results over complete coverage of current political boundaries, we are able to provide a new register which lists 261 international rivers, covering 45.3% of the land-surface of the earth (excluding Antarctica). This paper lists all international rivers with their watershed areas, the nations which share each watershed, their respective territorial percentages, and notes on changes or disputes in international boundaries since 1978.
Water has been named as likely to be the most pressing environmental concerns of the next century (American Academy of Arts and Sciences 1994).As global populations and economies continue to grow exponentially, and as environmental change threatens both the quantity and quality of the world’s fresh water resources, attention has increasingly focused on the state and management of those resources.
Waters which cross political boundaries have additional complexities brought on by strains in riparian relations and institutional limitations.Recent studies, particularly in the field of environmental security, have focused on the conflict potential of these international waters.Some stress the dangers of violence over international waters (see, for example, Westing 1986, Gleick 1993, Homer-Dixon 1994, Remans 1995, and Samson and Charrier 1997), while others argue more strongly for the possibilities and historic evidence of cooperation between co-riparians (see Libiszewski 1995, Salman and de Chazournes 1998, and Wolf 1998).Regardless of hydropolitical interpretations, interest in international waterways and the literature of comparative analysis is rapidly increasing (2) Kliot (1995) and, later with colleagues (Kliot, Shmueli, and Shamir 1997), compares five international basins and evaluates their respective management institutions; Wolf (1997) offers hydropolitical lessons learned from fourteen detailed case studies and 146 water treaties; Gleick (1998) includes a chapter on international waters in his biennial report on the world’s water; and Elhance (1999) describes the transboundary waters of the third world.
One critical aid in the assessment of international waters has been the Register of International Rivers (United Nations 1978) – a compendium which lists 214 international waterways, covering 47% of the earth's continental land-surface, compiled by the now-defunct Department of Economic and Social Affairs of the United Nations.The Register lists all international rivers by continent, along with their watershed areas, the nations that share each watershed, and their respective territorial percentages.Subsequent sections list countries that share watersheds, rivers and lakes that form boundaries, and related treaties. Most literature that, even peripherally, addresses the issue of international waters refers to the Register, and uses its data for analysis.The Register, however,was last updated in 1978.The information it reported has become dated by the many geopolitical changes of over the last 22 years, and by changes in map coverage and technology.
The purpose of this paper is to update the Register, taking advantage of global digital information that has become available, the detailed watershed analysis performed at the U.S. Geological Survey EROS Data Center, the extensive holdings of map libraries at the University of Alabama and Oregon State University, and a thorough compilation of boundary changes since the Register was last updated.Our work is the result of four years of study and the close collaboration between the facilities and expertise at the EROS Data Center and Oregon State University (3), and is a component of the Transboundary Freshwater Dispute Database.The Database is housed in the Department of Geosciences at Oregon State University, and includes a digital compilation of 150 international treaties and 39 U.S. compacts, hard copy files of negotiating notes and background material on fourteen case-studies of conflict resolution, news files on cases of acute water-related conflict, assessments of indigenous/traditional methods of water conflict resolution, and an annotated bibliography on the state of the art of international water dispute resolution (4).
The idea for the first Register of International Rivers originated with a 1958 United Nations panel of experts, whose report was entitled, “Integrated River Basin Development,” a revised edition of which included a world map showing 166 international river basins (United Nations 1978).The next and last revision was the 1978 Register, which identified 214 international basins.Despite being a desk study using only a polar planimeter solely on maps available at the UN Map Library, it was quite a sophisticated document for its time.
Nevertheless, a great deal has changed since 1978, both in map coverage and technology – notably the addition to the cartographic arsenal of digital and remote sensing data –and in the political boundaries which rivers cross.Our update, by necessity, took tracks along both lines: updating the river basins, and updating the political boundaries.
Roughly following the 1978 Register, we define a “river basin” as the area which contributes hydrologically (including both surface- and groundwater) to a first order stream, which, in turn, is defined by its outlet to the ocean or to a terminal (closed) lake or inland sea.Thus, “river basin” is synonymous with what is referred to in the U.S. as a “watershed” and in the UK as a “catchment” (5). We define such a basin as “international” if any perennial (6) tributary crosses the political boundaries of two or more nations (7).
By defining these basins by their ultimate outlet, we often group systems together that are commonly thought of as separate, even when they are treated as distinct politically.This situation occurs whenever the confluence of even major river systems takes place upstream of the outlet, such as on the Tigris-Euphrates and on the Ganges-Brahmaputra-Meghna systems.The Meuse, commonly treated by Europeans (and by the 1978 Register) as separate and distinct, is hydrologically part of the Rhine system, and is listed as such here.
This methodology brings up an important point: a register such as this is useful only inasmuch as one recognizes its limitations.Its strength lies in its identification of the location and extent of international basins.The number of such basins is less important.As noted above, many major tributary systems are treated for all management intents and purposes as separate.In the most detailed critique of the 1978 Register, Biswas (1993) points out, for example, that India and Bangladesh have identified more than 140 common water systems – all of which are grouped here together under three hydrologic units – the Fenney, the Ganges-Brahmaputra-Meghna, and the Karnafauli.Biswas also points to the limited treatment of groundwater in the 1978 Register.This issue is of lesser concern, since the vast majority of groundwater used for human purposes is in relatively shallow, unconfined aquifers, where the surface divide coincides with the groundwater divide, and which would thus be captured in our listing (Newson 1992; Postel 1999, personal communication 1999).Nevertheless, discussions of the management of international basins often revolve around issues not reported here, such as river flows and their contribution by each country, historic uses and future demand, and the social, ecological, and economic needs of each nation.
As with any cartographic project, we needed a base map to guarantee a minimum scale for consistency across the globe.Our close collaboration with the US Geological Survey’s EROS Data Center (EDC) gave us access to their ongoing advances in hydrologic applications of global digital elevation models (DEMs) for this purpose.EDC has recently released a global DEM, called GTOPO30.At a resolution of 30 arc-seconds, GTOPO30 was developed to meet the needs of the geospatial data user community for regional and continental-scale topographic data (Gesch 1994; Gesch, Verdin, and Greenlee, 1999).
A new geographic database developed at the EDC from GTOPO30 is HYDRO1K.It is designed to provide global coverage of topographically derived data sets at a nominal resolution of one kilometer.HYDRO1k provides a consistent base-line of hydrologic derivatives that are needed in many environmental, climatic, and water resource studies (8). The core data layer is the hydrologically correct DEM, which is obtained directly from the GTOPO30 data set.In order for the DEM to correctly model water movement across the land surface, the elevation data were processed to remove spurious anomalies that interfere with hydrologically correct flow (9). It is essential to develop a hydrologically correct DEM to ensure that derived drainage basins and synthetic streamlines closely represent real-world hydrology.
HYDRO1k provides a base map and minimum unified scale of at least 1:1,000,000 for this register.Nevertheless, these data sets are computer constructs and mathematical interpretations.As such, we found them to be extremely useful both as a starting point and as a basis for minimum standards, but also found that comparison with alternative sources, both digital and hardcopy, was necessary.Fortunately, other good spatial data sets exist, such as Environmental Systems Research Institute’s (ESRI) Digital Chart of the World, and the “Watersheds of the World” files included on the GlobalArc data set, developed by the Center for Remote Sensing and Spatial Analysis of Rutgers University, along with the U.S. Army Corps of Engineers Construction Engineering Research Laboratory (10). The U.S. Geological Survey’s EROS Data Center has also developed a DEM for the conterminous U.S. at a scale of 1:24,000.This DEM features a spatial resolution of 30 meters that covers a smaller area than GTOPO30 and allows for greater detail.
Finally, recognizing the limitations of digital data, particularly where topographic relief is low, we relied quite heavily on the extensive hardcopy holdings of the University of Alabama map library and the expertise of Tom Kallsen, the library’s director.Between an array of air photos, topographic map sheets, and the detailed coverages of various nations, we were regularly able to delineate basins at scales of 1:100,000, often at 1:40,000, and occasionally at 1:20,000.The basins which were digitized for this register, then, include our best judgement of the data available at this time, and finally deviated from HYDRO1k about 20% of the time (11).
Major geopolitical shifts have taken place since 1978, most of which are manifested in the boundaries between nations.These changes had the effect mostly of internationalizing national basins, notably the break-up of the Soviet Union and balkanization of the Balkans.To a much lesser degree, though, the opposite was true: two basins which were international in 1978 have become national, due to the unification of Yemen and of Germany.
The best digital set of international boundaries are those included in the Digital Chart of the World.However, given the political volatility of the times, this data set was not entirely up to date as we went to press, nor does it document where boundary ambiguities exist between nations.Since these ambiguities within international basins can have serious hydropolitical implications, we felt it important to document them, and to include them in area calculations wherever possible.As noted in the table footnotes, we relied heavily on the CIA World Factbook (1998), the Columbia Gazetteer of the World (Cohen 1998) and, especially, on the work of the International Boundary Resource Unit of Durham University (1999; personal communications 1999).
The 1978 Register listed 214 international basins, covering 47% of the world’s land surface (excluding Antarctica) (12). Our update lists 261 international basins (see Maps 1-6 and Table 4: International River 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:
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 Map 7 and 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:
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.
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.