SAN ANTONIO — The drought that has turned Texas and parts of the Plains into a parched moonscape of cracked earth could persist into next year, prolonging the misery of farmers and ranchers who have endured a dry spell that is now expected to be the state’s worst since the 1950s.

The U.S. Climate Prediction Center said Thursday that the La Nina weather phenomenon blamed for the crippling lack of rain might be back soon, just two months after the last La Nina ended. If that happens, the drought would almost certainly extend into 2012.

The extreme dry conditions have been made worse by week after week of triple-digit temperatures, which have caused reservoirs to evaporate, crops to wither and animals and fish to die off by the thousands.

“The suffering and desperate need for relief grows with the rising temperatures and record-breaking heat that continue to scorch Texas with each passing day,” state Agricultural Commissioner Todd Staples said.

Even the state’s feral hogs are hiding from the heat, postponing a new reality TV show about Texans gunning them down from helicopters.

Texas saw less than an inch of rain statewide in July, and more than 90 percent of the state is already in the two most extreme stages of drought.

“Anything below 2 to 3 inches of rainfall would be a fly-on-the-windshield type thing as far as improvement,” said Victor Murphy, a climate expert with the National Weather Service. “It wouldn’t reverse this continued death spiral we’re on.”

Also Thursday, the state climatologist declared this the most severe one-year drought on record in Texas. Officials expected to declare soon that it has become the worst drought since the 1950s.

A newly updated weather map showed the drought holding firm — if not intensifying — through at least October.

In Dallas, county officials say at least 13 people have died from the heat this summer. The high temperature Thursday was expected to hit 109 degrees, which would be a record for the date.

Statewide demand for power was expected to approach the maximum Thursday for a fourth straight day. Some large industrial plants were forced off the overburdened electric grid, requiring them to shut down or rely on their own power reserves.

And for the first time this summer, utilities warned residential customers of the potential for rolling outages.

Beleaguered farms and dead pastures have been hurt the most. The agriculture industry, which accounts for nearly 9 percent of the Texas economy, may be headed for the biggest single-year losses ever — potentially as high as $8 billion, according to the Texas AgriLife Extension Service.

The La Nina watch issued by the Climate Prediction Center warned that the phenomenon marked by a cooling of the tropical Pacific Ocean could soon redevelop. La Nina typically results in less rain for southern states, and it’s blamed for drought conditions in Oklahoma and New Mexico, too.

A La Nina watch means conditions are favorable for La Nina to return within the next six months. But Texas will probably know as early as October or November, said Mike Halpert, a deputy director of the Climate Prediction Center.

By that time, the driest places could be out of water.

In the town of Robert Lee, a rural farming community of about 1,000 in the middle of West Texas, people are worried that Lake E.V. Spence could dry up by winter and leave the town without any water.

Some residents wonder if the National Guard can haul in water. Making matters worse, a pipe that was probably busted by the dry, shifting ground began gushing water the town cannot spare. City workers scrambled Thursday to fix it.

Closer to Austin, the Llano River trickled at a rate about 95 percent slower than normal. The city of Llano already has contacted bottled water distributors about supplying residents with bottles for cooking and drinking if the river flow stops entirely, which could happen in a matter of weeks.

“It’s amazing we’re still getting what water we are,” City Manager Finley deGraffenried said. “We’re running 107 degrees yesterday and the day before. It’s unbearable.”

Texas received no significant rain in April or May, which are typically the state’s wettest months. Lake levels are so low that earlier this week, a massive chunk of the space shuttle Columbia that broke apart over Texas in 2003 was found poking out of the receded waters of Lake Nacogdoches.

About 70 percent of Texas rangeland and pastures are classified as being in very poor condition, which means there has been complete or near-complete crop failure or there’s no food for grazing livestock.

One of the most memorable droughts occurred in the 1950s, when a decade of below-average rainfall and long dry spells actually changed the state’s demographics, with many families fleeing parched farms for cities. Experts say the current drought is nowhere near so severe, but if it continues, the scarcity of water will be painful.

In the mid-1950s, Texas had a population of 7 million.

“We got a state with 25 million now. You can see the impact would be significantly greater if we had a drought that the 1950s had,” said Travis Miller, a member of the state’s Drought Preparedness Council and AgriLife Extension Service leader.

One upside is that second La Ninas are historically weaker than the first, Halpert said.

The formation of La Nina also doesn’t guarantee there won’t be significant rain. The pattern often makes for a more active hurricane season, which could lash Texas with a soaking storm. Forecasters said Thursday they still see a busy hurricane season ahead, calling for 14 to 19 tropical storms.

“If I was in Texas, this is not great news,” Halpert said. “But it’s not the end of the world.”