By David Alire Garcia

MEXICO CITY (Reuters) - A growing body of scientific evidence ranks Mexico and its southern neighbors near the top of the list of countries most vulnerable to global warming, and advances in micro-forecasting foresee a grim future in alarming detail.

According to two new studies, a deadly combination of warmer weather and less rainfall in the years ahead will devastate yields of traditional crops like corn and beans, as well as the region's market-critical coffee harvest.

The ultra-local projections with shorter time horizons - as soon as the 2020s - include color-coded maps that for the first time provide virtually farm-specific climate change predictions, an innovation scientists hope will convince local stakeholders to plan accordingly.

That could mean switching to new seeds, shifting to hardier crops, or even abandoning long-established family farms.

The new research dissects the region that gave birth to modern corn and today produces a fifth of the world's high-end Arabica coffee beans, offering predictions at a level of detail of just one square kilometer, a leap in precision.

"There's a lot of potential here," said Jerry Meehl, a climate change scientist who shared in the 2007 Nobel Peace Prize won by the Intergovernmental Panel on Climate Change and former U.S. Vice President Al Gore. "What you want at the end of the day is information people can use."

According to Meehl, head of climate and global dynamics at the National Center for Atmospheric Research in Boulder, Colorado, the latest downscaled studies for agriculture in Mexico and Central America are among the highest-resolution climate change projections anywhere in the world.

The same countries are among the most threatened by climate change.

Mexico stands to lose between a quarter and a third of its agricultural production by 2080, according to a study by William Cline of the Washington, D.C.-based Center for Global Development. That is more than any country besides India.

"Now we have to focus on mitigation strategies that can make the impact we feel less painful," said Francisco Mayorga just before he left office as Mexico's agriculture minister on December 1.

Central America will see agricultural output shrink between 12 and 24 percent, according to Cline, a loss cushioned by the region's average rainfall of some 6 millimeters per day, compared with Mexico's 2 millimeters per day.

"The fundamental problem is that water needs will go up as the heat rises, but unfortunately these countries will be getting less water," said Cline.

As a result, land suitable for coffee growing in parts of Central America is expected to shrivel by up to 80 percent by 2050, one of the micro-forecasts published this year said.

To head off the slow-motion catastrophe, the region's governments are investing millions of dollars in the development of better seeds and better-trained farmers, among other things.

Mexico alone has spent $49 million since 2011, and has pledged another $138 million over the next decade. But as land begins to yield less, the region is bracing for tougher times.

TOUGH TIMES

"It was like a horror movie," said corn farmer Reymundo Ruiz, speaking of a recent worm infestation that was followed by unexpected freezes and a prolonged drought.

"In the past, there were changes in the weather," said Ruiz, who tends an eight-hectare (20-acre) farm in the central Mexican state of Tlaxcala. "But not as big, not as drastic."

In the spring, the International Center for Tropical Agriculture (CIAT) published a study that forecasts the impact of climate change on coffee production for 1-square-kilometer grids in Nicaragua, El Salvador, Guatemala and Mexico.

The micro-forecast stems from global models that reduce weather predictions to grids as small as 100 square kilometers, using supercomputers crunching mountains of oceanic and atmospheric data. The models are then statistically downscaled, incorporating local data to yield the 1-square-kilometer projections.

The CIAT study found that by 2050, rising average annual temperatures between 2 to 2.5 degrees Celsius will cause local coffee farming to dip sharply. The countries surveyed will see on average between 5 to 10 percent less rainfall each year.

Warmer weather could cut coffee output in El Salvador by up to 81 percent, by nearly 60 percent in Nicaragua, and nearly half in Guatemala and Mexico, the CIAT report said.

The region's more than 500,000 coffee farmers, the vast majority of whom tend to plantings smaller than 5 hectares, will face tough choices if the projections prove accurate. Continued...