C L IMATEwatch

Decades of drought predicted for southwest USA

THE SOUTHWEST USA could be experiencing decades-long periods of drought in the not-too-distant future, according to new research led by scientists at the University of Arizona.

By reviewing previous research into the historical climate of the southwest USA, Connie Woodhouse and her colleagues were able to model future climate in the region and identify a plausible worst-case scenario that includes a 60-year drought. ‘We’re not saying future droughts will be worse than what we see in the palaeo record, but we are saying they could be as bad,’ Woodhouse said. ‘However, the effects of such a worstcase drought, were it to recur in the future, would be greatly intensified by even warmer temperatures.’

The worst warm-climate drought in the southwest within the past 1,200 years was 60 years long and occurred during the mid-12th century, according to research by one of Woodhouse’s co-authors, David Meko, and others. ‘Even without warming, if you had one of those medieval droughts now, the impact would be devastating,’ Woodhouse said. ‘Our water systems aren’t built to sustain us through that length of drought.’

The flow of the Colorado River (above) recorded at Lees Ferry between 2000 and 2009 is the lowest on record, and according to Woodhouse, the current drought could be part of a longer dry period. Other research has predicted that changes in atmospheric circulation will reduce the amount of winter precipitation that falls in the southwest, she said.

■ Greek reptiles offer glimpse of warming’s possible impact: A wave of reptile extinctions that took place on the Greek islands over the past 15,000 years may provide information about how plant and animal populations will respond to future global warming, according to a University of Michigan ecologist and his colleagues.

As sea levels rose in response to warming at the end of the last ice age, parts of the Greek mainland were cut off to form islands. The changing climate also caused forests to shrink as the area became more arid. Many of the reptile populations on the newly formed islands perished as a result of the restriction of their ranges and the changes in vegetation and climate.

In a paper published in American Naturalist, Johannes Foufopoulos and his colleagues used the presence or absence of 35 reptile species on 87 Greek islands that were once connected to the mainland to calculate the rates of extinction of the different species. They found that populations disappeared from the smallest islands – where habitat choices would be most limited – first, and that ‘habitat specialists’ were especially hard hit. Those whose distributions tended to be in cooler, moister, more northerly regions also tended to show higher extinction rates.

The researchers warned that the increasing fragmentation of natural habitats could drive a similar pattern of extinctions in the future. ‘The widespread fragmentation of natural habitats greatly exacerbates the effects of climate change and undermines the ability of species to adapt to new conditions,’ Foufopoulos said.

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12 www.geographical.co.uk FEBRUARY 2011