EJIDO LA LAGUNA, Mexico (Reuters) - Julian Rosales' farm is within a stone's throw of one of North America's biggest rivers, but the Mexican landowner fears he will not be able to sow his crops next year for lack of water.
Rusty tractors plow Rosales' parched earth along the banks of the Rio Grande on Mexico's border with Texas where thousands of local farmers say their livelihoods are at stake because Mexico was this year forced by a bilateral treaty to transfer millions of liters of water to the United States.
While farmers and lawmakers in arid northern Mexico seek to challenge the water payment in an international court, the farmers' plight is a symptom of a much bigger problem: the Rio Grande and its underground aquifers are being sucked dry on both sides of the frontier.
The eastern border region is slowly heading toward a water crisis.
"They have taken our water and these lands are dying. Our children are emigrating to the United States, some illegally," said Rosales, who grows the animal feed sorghum in the desert lands of Mexico's Tamaulipas state on the Gulf of Mexico.
Under a 1944 treaty, Mexico is required to transfer water to the United States every five years from the two dams the countries share on the Texas border. For farmers in Tamaulipas, that means ruined harvests and hardship every time the transfer is made.
The landscape is now dotted with abandoned farms and villages unable to enjoy the artificial irrigation that is central to agriculture in a desert region with sporadic rains.
In a last attempt to save the farmers, lawmakers in Tamaulipas have called on Mexico's Supreme Court to rule on whether this year's water transfer was lawful. They argue the treaty stipulates the payment should be made with water from six Mexican tributaries further west along the border that feed the Rio Grande, not with surface water from Tamaulipas.
If they win, lawmakers aim to take the United States to an international court to force it to return the water.
Water is a scarce commodity across the 2,000-mile (3,200-km) U.S.-Mexico border, with the fight over the Rio Grande mirrored in the west by competition for the Colorado River, which is reduced to a trickle by the time it reaches its delta in the Sea of Cortez in Mexico.
In eastern Mexico, the tributaries that feed the Rio Grande are being siphoned off to support vegetable crops for export in the desert. On the U.S. side in Colorado, water from the Rio Grande is so heavily diverted for human use that a section of the river in El Paso on the Texas border virtually stops.
Springs across southern Texas have run dry as aquifers are pumped for water. Most could be exhausted within two decades.
Historically, the Rio Grande, the fifth-longest river in the United States, flowed continuously from Colorado to the Gulf of Mexico. But since the 1900s, dams, channelization and overexploitation have endangered its survival.
"The Rio Grande is one of the most stressed river basins in the world and water use is already at its limit," said Casey Walsh, a water specialist Mexico's Iberoamericana University.
That is worrisome given that Mexican cities on the border with Texas are set to double their population over the next 20 years. Trade growth, a retiree boom and the influx of immigrants in south Texas will also substantially increase water demand there, as small towns become cities.
The Mexico-Texas border is also a motor for both the U.S. and Mexican economies. Billions of dollars in trade pass through the frontier every year and the U.S. city of Laredo is one of the United States' biggest inland ports.
A dry Rio Grande is unthinkable for Americans and Mexicans. Known in Spanish as the Rio Bravo, or "Rough River," its waters have been famed in Western movies and cowboy ballads and have marked the Texan border with Mexico since the 19th century.
"It is going to be disastrous unless there is a change. Companies, farmers, and government at the local, state and federal levels need to work out a solution," said Leslie Hopper of the Texas-based Sul Ross State University, which has set up a research center to study the Rio Grande.
El Paso, which faced predictions it would run out of water in 2010, has done the most to tackle the water shortages. In August, the city opened the world's largest inland desalination plant to turn brackish ground water into freshwater and ensure decades of water supply.
The city of Brownsville on the Gulf of Mexico is now considering a $150 million desalination plant, while Mexico's Tamaulipas' state government has proposed a $500 million plan to build an aqueduct to channel Rio Grande water into pipes.
"Without this, we will continue to lose half of our water to seepage and evaporation," said Jaime Cano, a director at the Tamaulipas state water commission.
Reporting by Robin Emmott; Editing by Eddie Evans