North America (28 percent), Africa (26 percent), and Europe (21 percent) also have sizable percentages of borders defined by rivers. The map below highlights several key rivers that define borders between Paraguay, Brazil, Argentina, and Uruguay. The map above highlights in blue all of the international borders defined by large rivers. Brazil, Colombia, Venezuela, Suriname, Guyana, French, Guiana, Bolivia, Paraguay, and Uruguay all have lengthy international river borders. Of all of the continents, South America stood out for having the largest proportion of international borders made up by rivers-nearly half. “One of the reasons we developed this dataset is that identifying subnational as well as national stakeholders with explicit geospatial mapping is an important first step toward the development of holistic river management.”Īccording to their analysis, rivers make up 23 percent of international borders, 17 percent of the world’s state and provincial borders, and 12 percent of all county-level local borders. “If a watershed were entirely within one jurisdiction, it would make many problems easier to address, but that is simply not the reality,” Smith said. Since rivers often sit between states, cities, and counties, they are routinely at the center of complex political controversies involving dams, hydropower, irrigation, flood management, and water pollution. As detailed in the journal Water Policy, Popelka and Smith merged political border and population density data with a map of large rivers (30 meters or wider) derived from Landsat data, making it possible to identify and map political borders at both national and subnational scales. With the help of Sarah Popelka, a student at UCLA, he set out to change that.Īfter several years of work, the researchers have released a new geospatial database of the world’s river borders- Global Subnational River-Borders (GRSP). However, he also was surprised to find that little quantitative research on river borders is available-and even less that makes use of modern geospatial mapping techniques. After visiting multiple rivers around the world, Smith became fascinated by the concept of the waterways as political borders. By providing fresh water, fertile land, and food-along with a convenient way to transport goods-rivers have long determined the locations of towns, cities, and ultimately entire civilizations.įertile river valleys were cradles to four of the earliest civilizations: the Tigris and Euphrates in Mesopotamia, the Nile in Egypt, the Indus in South Asia, and the Yangtze and Yellow in China, explained Brown University geographer Laurence Smith.Īt the same time, rivers have long been used to divide lands. Rivers have long united people, so much so that a world without rivers would be unrecognizable.
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