As climate change alters rainfall patterns and river flows, tensions are bound to rise between states and countries that share rivers that cross their borders.

 

In the Rio Grande Basin of the American Southwest, that future inevitability has arrived.

 

Last week Texas, suffering through a devastating drought, filed a lawsuit with the U.S. Supreme Court alleging that New Mexico is failing to live up to its water delivery commitments under the 1938 Rio Grande Compact.

 

The Rio Grande rises in the San Juan Mountains of Colorado and flows 1,900 miles before entering the Gulf of Mexico.

 

Texas charges that New Mexico’s pumping of groundwater in the region below Elephant Butte Dam to the New Mexico-Texas border is reducing Rio Grande flows into Texas, thereby depriving the state’s farms and cities of water they are legally entitled to under the Compact.

 

Texas v. New Mexico is likely to be but one of a string of disputes that erupt as drought causes water supplies to dwindle and water-sharing pacts devised in wetter and less-populated times can no longer hold the peace.

 

Texas doesn’t specify how much water it believes New Mexico is illegally withholding, but indicates it is sufficient to irrigate thousands of acres of farmland.  The city of El Paso also relies on Rio Grande water for half of its supply.

 

New Mexico officials have consistently maintained that the state is sending to Texas all the Rio Grande water to which it is legally entitled.  The state attorney general said in a recent statement that Texas is “trying to rustle New Mexico’s water and using a lawsuit to extort an agreement that would only benefit Texas while destroying water resources for hundreds of thousands of New Mexicans.”

 

Fighting words, to be sure.

 

If the Supreme Court justices decide to take up the case, they would do well to first sign up for hydrology 101.

 

One of the great water myths is that rivers and underground aquifers are separate and distinct sources of water.  In reality, rivers and groundwater are often intimately connected.  Groundwater provides the “base” flow that keeps many rivers running during dry times. For their part, rivers and irrigation canals leak water into the subsurface, recharging the aquifers below.

 

In dry years, when surface supplies run low, farmers often turn to underground water to replace or supplement their irrigation supply.  That’s what New Mexico farmers downstream of Elephant Butte have done during years of drought and low river flows.

 

In the Mesilla Basin, for example, groundwater is the primary source of irrigation water for about 5,000 acres, but is a supplemental source of supply for more than 70,000 acres.  So in dry times, groundwater withdrawals ratchet up.

 

According to an article on the impacts of groundwater pumping in the Rio Grande Basin published in this month’s Ecosphere, a journal of the Ecological Society of America, during the 2004 drought, when federal officials curtailed releases from Elephant Butte Dam, pumping from the Messila Aquifer rose to twice the long-term average.

 

The drought of recent years has elicited a similar response from farmers, and groundwater pumping in the Rio Grande Valley has increased markedly. But how much this pumping has affected flows into Texas is in question.

 

The current bi-state conflict began in 2007 when Texas farmers complained that New Mexico was extracting too much groundwater.  To avoid an escalating legal fight, the federal Bureau of Reclamation, which operates Elephant Butte, worked out an agreement with two irrigation districts in Texas and New Mexico to give Texas more river water to make up for New Mexico’s groundwater use.

 

That agreement didn’t sit well with New Mexico officials, however, and three years later the state filed suit against the Bureau, charging that the deal gave away too much of New Mexico’s Rio Grande allotment to Texas and would cause $183 million in damages to the state’s agricultural economy.

 

Texas shot back with the lawsuit filed last week.

 

Meanwhile, the drought persists. Elephant Butte is at 8 percent of its storage capacity, the same as when I visited the reservoir last August.

 

While the legal case may drag on for years, it is a wake-up call for all states and nations that share transboundary waters to proactively add resilience to their treaties and institutions before crises hit, and even more importantly, to develop workable governing structures over water where they are lacking.

 

It is also a lesson to invest now in water efficiency improvements so as to reduce pressures on both rivers and aquifers.

 

Because while the Supreme Court may ultimately decide this Texas-sized water dispute, even the highest court in the land can’t dictate Mother Nature to deliver more water.