US Southwest Could See Decades-long Drought: Study

Posted on: Tuesday, 14 December 2010, 06:25 CST

An unprecedented, decades-long combination of heat and drought could be headed to the Southwest United States sometime this century, according to a new study by researchers at the University of Arizona.

The scientists reviewed previous studies of temperature changes and droughts in the region over the past 1,200 years, and concluded that a 60-year drought similar to the one that occurred during the 12th Century could be in our future.

"Major 20th century droughts pale in comparison to droughts documented in paleoclimatic records over the past two millennia," the researchers wrote, referring to the elevated temperatures combined with lengthy and widespread droughts that occurred during the Medieval period.

By determining the dates and duration of coinciding drought and warm temperatures in the past, the researchers identified plausible worst-case scenarios for the future. 

Such scenarios can often help water and other resource managers plan for the future, the scientists said.

"We're not saying future droughts will be worse than what we see in the paleo record, but we are saying they could be as bad," said Connie Woodhouse, a UA associate professor of geography and regional development and the study’s lead author.

"However, the effects of such a worst-case drought, were it to recur in the future, would be greatly intensified by even warmer temperatures."

There have been several periods of intense, sustained drought that affected much of western North America over the past 2,000 years.

David Meko, the study’s co-author and an associate research professor in the UA's Laboratory of Tree-Ring Research, noted that droughts that are accompanied by warm temperatures have more severe impacts on ecosystems.

During the Medieval period, temperatures were about 1.8 degrees Fahrenheit (1 C) above the long-term average.

However, average temperatures in the Southwest U.S. have been warmer than that since 1990, and are projected to rise at least another 3.6 F (2 C) by 2100, Woodhouse added.

The most severe warm-climate drought in the Southwest during the past 1,200 years occurred during the mid-12th century and lasted 60 years, covering most of the modern day western U.S. and northern Mexico.

For 25 years during that drought, the Colorado River flow averaged 15 percent below normal, the researchers said. 

The Colorado River supplies water for agriculture and cities, including Los Angeles, Las Vegas, Denver, Phoenix, Tucson and Albuquerque, in seven western U.S. states and two states in northwestern Mexico.

Over the past decade, sampling shows that the river is at its lowest point since 1906, when records first began being kept.

"As this drought unfolds you can't really evaluate it until you're looking back in time," said Woodhouse.

In the future, the Colorado River flow is projected to decrease between two and eight percent for every 1.8 degree Fahrenheit (1 C) of warming, wrote Woodhouse and her colleagues.

"Even without warming, if you had one of those medieval droughts now, the impact would be devastating," she said.

"Our water systems are not built to sustain us through that length of drought."

"The bottom line is, we could have a Medieval-style drought with even warmer temperatures.”

The study is part of a special feature entitled "Climate Change and Water in Southwestern North America”, which appears in the December 13 online edition of the Proceedings of the National Academy of Sciences.

The paper by Woodhouse and her colleagues is entitled "A 1,200-year perspective of 21st century drought in the southwestern North America."  Co-authors include Glen MacDonald of the University of California, Los Angeles, Dave Stahle of the University of Arkansas in Fayetteville and Edward Cook of Lamont-Doherty Earth Observatory of Columbia University.

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Image 1: Annual tree rings record a detailed history of drought (narrow rings) and wetness (wide rings). This sample from a dead Douglas-fir tree in the Santa Catalina Mountains near Tucson, Ariz., has nearly 400 rings and dates back to the year 1600. Stress cracks, visible in the foreground of the image, occur as the dead wood dries and contracts. Credit: Copyright Daniel Griffin

Image 2: A core extracted from a living Douglas-fir tree in the Santa Rita Mountains south of Tucson, Ariz. Scientists use such cores to study the annual rings of trees, visible on the core as banding. Collecting such cores causes only temporary injury to the tree. Credit: Copyright 2009 Daniel Griffin

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Oil will run out 100 years before new fuels developed - US study

AFP quoted US study as saying that the world will run out of oil around 100 years before replacement energy sources are available if oil use and development of new fuels continue at the current pace.

UC Davis researchers at the University of California used the current share prices of oil companies and alternative energy companies to predict when replacement fuels will be ready to fill the gap left when oil runs dry.

The study said that if the world’s oil reserves were the 1.332 trillion barrels estimated in 2008 and oil consumption stood at 85.22 million barrels per day and growing yearly at 1.3% oil would be depleted by 2041.

But by plugging current stock market prices into a complex equation, Mr Debbie Niemeier UC Davis engineering professor and Ms Nataliya Malyshkina postdoctoral researcher calculated that a viable alternative fuel to oil will not be available before the middle of next century.

The researchers analyzed the share prices of 25 oil companies quoted on US, European and Australian stock exchanges and of 44 alternative energy companies that produce fuels such as ethanol or bio diesel or are developing fuel cells, batteries and propulsion systems aimed at replacing gasoline and diesel in vehicles of the future.

Ms Malyshkina said that what they found is that the market capitalization or total value of all stock shares of traditional oil companies far outstripped that of the alternative energy companies. That indicated to them that investors believe oil is going to do well in the near future and occupy a larger share of the energy market than alternative energy.

She said that to assess the time until a considerable fraction of oil is likely to be replaced by alternatives we used advanced pricing equations to make sense of the large discrepancy between the market capitalization of traditional oil companies and the market capitalization of alternative-energy companies.

Their calculations showed that there would not be a widely available replacement for oil-based fuels before 2140 which, even if the more optimistic date of 2054 for oil depletion is retained would mean there could be a gap of around 90 years when it might be difficult to run a motor vehicle.

Ms Malyshkina said that nearly two thirds of crude oil is used to produce gasoline and diesel to run vehicles. The researchers’ calculations were based on the theory that long-term investors are good predictors of when new technologies will become commonplace.

She said that sophisticated investors tend to put considerable effort into collecting, processing and understanding information relevant to the future cash flows paid by securities. As a result, market forecasts of future events, representing consensus predictions of a large number of investors, tend to be relatively accurate. Similar calculations have been used to accurately predict the outcome of elections and the results of sports events.

(Sourced from AFP)