NewsSeptember 7, 2011

Global Warming Amplifying Texas Drought, Wildfires, Scientists Say

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Alyson Kenward

By Alyson Kenward

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Just when it looked like weather conditions couldn’t get any worse in Texas, a new wildfire burning outside of Austin destroyed nearly 800 homes in the past few days. This came on the heels of the state's hottest and driest summer in recorded history, with many parts of the state smashing all-time records by wide margins. Yesterday, Texas state climatologist John Nielsen-Gammon announced this was the hottest summer on record for Texas — and the hottest summer ever for any U.S. state, based on preliminary numbers — and last month he declared Texas is in the midst of its worst one-year drought on record. The blend of hot weather and parched land has made for perfect fire conditions, and this has been the worst year for Texas wildfires in over a decade. Nearly 3.6 million acres of the “Lone Star State” have burned so far this year, an area roughly the size of Connecticut.

The heat and drought are record-breaking, but how unusual are they? According to Nielsen-Gammon’s own blog, it’s in a category unto itself:

“The year 2011 continues the recent trend of being much warmer than the historical precipitation-temperature relationship would indicate, although with no previous points so dry it’s hard to say exactly what history would say about a summer such as this one. Except that this summer is way beyond the previous envelope of summer temperature and precipitation,” Nielson-Gammon wrote.

In Texas, the summer of 2011 has been both the hottest and driest on record. The drought has cost billions in economic losses, mainly due to agricultural impacts and from wildfires. Credit: John Nielsen-Gammon, Texas State Climatologist.

Not only is this summer the hottest (highest up on the graph) and the driest (farthest to the left), but it also appears to have a more significant connection between the temperature and drought than what’s been seen before. 

The exceptional drought in Texas and neighboring states set in almost a year ago, when La Niña conditions were present in the tropical Pacific Ocean, with cooler-than-average ocean temperatures that helped alter global weather patterns. Typically, La Niña years are accompanied by below average rainfall in the American Southwest. 

Since the spring, every month in Texas has been among that month's top ten driest on record, and by summer’s peak, there was virtually no moisture left in the ground, says Victor Murphy, the climate service program manager for the National Weather Service’s southern region. Without moisture to help keep the ground cool, he explains, temperatures soared.

“In this case, the drought certainly came first,” says Murphy, “but the drought begets heat, and the heat begets more drought. It’s an extreme leading to more extremes.”

The current drought is worse than any other that most Texans can remember, and it also comes after nearly a decade of drought across most of the Southwest.

According to climate scientist Richard Seager of Columbia University’s Lamont Doherty Earth Observatory, it’s very hard to say how much human-induced climate change has contributed to this year’s scorching temperatures, drought, and related wildfires in Texas. But Seager says that, while La Niña, as well as warm waters in the tropical North Atlantic Ocean, have been the main causes of the extreme drought, there is also evidence that the region is drying as a consequence of manmade global warming.

Texas is in the midst of its worst recorded one-year drought. Scientists say that climate change may have amplified the drought, which was otherwise caused by natural climate variability. Credit: MyEyeSees/flickr.

“The human-induced components of this [ongoing drought] so far are pretty weak, but I think it’s there,” Seager says. Even in the absence of La Niña’s natural effects, he explains that global warming is making areas like Texas drier than they were for much of the last century. “What you have is background drying, and then the natural variability superimposed on it.”

Moreover, average temperatures in Texas are on the rise. Over the entire year, Texas has been about 1.5°F warmer than it was in the 1980s and 1990s. That doesn’t sound like a big difference, but over several years, the warmer temperatures exacerbate the increasing aridity. And that’s not all.

“These are fairly small changes in average temperature, but even small changes can produce very big changes in extreme events,” says Jerry Meehl, a climate scientist at the National Center for Atmospheric Research (NCAR), during a press briefing today on this year's billion-dollar extreme weather events. For example, because the Texas region has become drier, and average temperatures are warmer than they used to be, the region was likely more susceptible to severe drought brought by La Niña than it would have been a few decades ago.

“When climate change and natural variability happen in the same direction, that’s when records get broken,” says NCAR climatologist Kevin Trenberth.

At the moment, climate models predict that La Niña may stage a comeback this winter, which means the Texas drought could continue. Eventually, however, Seager says the tropical Pacific will warm up and the worst of this drought will subside. “We don’t expect it to be this dry consistently,” he says. “This won’t be what the climate will be like throughout the 21st century.” 

On the other hand, Seager says that climate change, driven by increasing amounts of greenhouse gases in our atmosphere, is tilting the scales in favor of future droughts that may look like this one. “The human induced component is making years like this one more likely.”