Many of the greatest rivers of the world, like the Rio Grande, demarcate the boundaries between countries. Rivers make up a staggering 23% of international borders.

A map of the Harirud River Basin, which flows through Afghanistan, Iran and Turkmenistan. Courtesy of Hugo Loaiciga

Meanwhile, others like the Tigris and Euphrates wind their way to the ocean with no regard for international boundaries. Undeterred by customs and immigration, their fluvial flow runs from one territory to the next, oblivious to their incredible geopolitical influence. Sometimes they align with international borders, other times not whatsoever. Even within a river system, incredible ecological, political and geographic variety is found. 

These transboundary rivers, as they are called, are much more than a water source. They are places of development and power generation, they define cultural identity and they can serve as sources of conflict and leverage in equal measure. More often than not, they become the subject of sometimes intense negotiations. 

“There are many, many transboundary basins. You know about the geopolitics in between Israel and the Palestinians, right? They, for instance, have some shared water resources that are very conflicting,” said Hugo Loaiciga, a hydrologist with the UC Santa Barbara Department of Geography. 

Particularly in the wake of intensifying climate change, the role of transboundary rivers in regional politics — and the damming and diverting of them — has fueled tensions around the world. The Grand Ethiopian Renaissance Dam is another example, a $5 billion project which remains an object of contention among Ethiopia, Sudan and Egypt. 

Loaiciga and his collaborators, including researchers at the University of Tehran and Texas A&M University, have long sought to understand the broader geopolitics of the region encompassing Afghanistan, Iran and Turkmenistan. 

In this most recent research, they have placed a microscope over the Harirud River Basin — or Herat River. The Harirud flows west from the snow-capped peaks of the Hindu Kush. From this origin, the river traverses Afghanistan, Iran and Turkmenistan before disappearing into the sands of the Karakum Desert.  

These largely arid regions rely heavily on irrigation, making these finite water resources doubly important. In addition, the rise of the Taliban in Afghanistan has further complicated the picture. As recently as August, Taliban fighters launched an attack on the Afghan-India Friendship Dam in Herat, which provides water and power to hundreds of thousands of people. 

Using machine learning and evolutionary game theory to analyze the long-term water-sharing strategies of the countries encompassing the basin, the researchers sought to find evolutionary stable strategies, which are persistent and cannot be changed or overcome by other strategies in a game that is played repeatedly. 

“Imagine you’re playing poker with four people and nobody knows what you’re doing. These countries can be a similar model. Their behavior towards sharing water resources can be posed as a game theory problem — then you [can] solve them based on their particular characteristics,” Loaiciga said. 

“You are involved in a situation where there are several people who are interested in the same thing. And so all of you are vying to get as much as possible from that resource.” 

In other words, the researchers used game theory to find the strategies among the different players which would net the most mutual benefits. 

With this, the researchers found that the evolutionarily stable strategy was the one in which the upstream country — which generally has more leverage than the downstream countries and more incentive not to cooperate — gets more benefits and incentives from cooperating than from not cooperating. 

So, what specifically does this mean for Afghanistan, Iran and Turkmenistan? 

“The one strategy that will provide the greatest benefits for the three countries is one where Iran pays for Afghanistan to reduce their withdrawal of water in their own country and allow Iran to make use of it,” Loaiciga said. 

“That’s the one strategy that will generate less conflict and that will produce the greatest gain because Iran has very active agriculture, so even though they are paying money to Afghanistan, they then take the water, and they produce a lot of agricultural products.”

“Meanwhile, Turkmenistan uses very little water. The best thing for them is to basically keep using the same water that they sporadically get because they have a very small agricultural economy and they only use a small amount of water for urban supply.”

Sean Crommelin
Sean Crommelin is the Science and Tech Editor for the Daily Nexus. He can be reached at