Tuesday, October 18, 2016

Megadrought 99 Percent Certain For Southwest by 2050 if Temperature Rise Continues, Study Says


Eric Chaney
Published: October 18, 2016

Tree rings in the American Southwest provide evidence of megadroughts that hit the region hundreds of years ago.

According to a new study from Cornell University, these droughts have been linked to the demise of civilizations, and changing climate conditions virtually assure that another one is on its way.

If precipitation decreases, stays them same, or even increases slightly in the coming years, there’s a 99 percent chance of a megadrought hitting the region, the study says.

“This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region,” Toby Ault, a professor of earth science at Cornell University and one of the authors of the study, told The Atlantic. “As we add greenhouse gasses into the atmosphere—and we haven’t put the brakes on stopping this — we are weighting the dice for megadrought conditions.”

Drought conditions come about when the natural "tug-of-war” between precipitation supply and evaporation becomes unbalanced, says a statement from Cornell. Higher temperatures lead to an “increase in atmospheric demand for moisture from the land surface will shift the soil moisture balance. If this happens, megadroughts will be far more likely for next millennium.”

In a business-as-usual world, the study says, rising temperatures alone are sufficient to drive megadrought risks to unprecedented levels.

University of Arizona professor and paleoclimatologist Jonathan Overpack, who invented the word megadrought in the 1990s, told The Atlantic the scenario laid out in the study, a “searing megadrought” by 2050, scares him.

“This isn’t like the drought of our grandfathers,” he said. “It’s a drought that everyone would agree would be devastating as all heck.”

Most research suggests it would be worse than any known drought in history, The Atlantic reports. Millions of trees would die, toxic dust storms would rage across the land, and agriculture would be all but impossible.

On the other hand, if regional warming remains below 2°C, megadrought risks will correspondingly remain below 66 percent for a wide range of precipitation changes.

“We found that megadrought risk depends strongly on temperature, which is somewhat good news,” Ault said in the Cornell release. “This means that an aggressive strategy for cutting greenhouse gas emissions could keep regional temperature changes from going beyond about 2 degrees Celsius.”

Adaptions to the region’s water policies - demand reduction, increased efficiency strategies, interbasin water transfers, shifts to groundwater reliance, increased surface irrigation - could also serve to offset some of the increase in atmospheric demand for moisture that higher temperatures will bring, the study says.

So there is light a the end of the tunnel.

“Megadrought risks are still likely to be higher in the future than they were in the past,” Ault said in the Cornell release. But, “efficient use of water resources in the drought-stricken American Southwest are likely to help that region thrive during a changing climate.”

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