The average speed of surface winds over most regions in the northern hemisphere have dropped significantly in the past three decades, according to a study published online by Nature magazine last month.
Scientists disagree on whether it is the start of a trend, the end of it, or whether there is a trend at all – nor can they fully explain what may have caused the phenomenon. But the finding is bad news for the wind power industry.
The study, carried out by a French team led by Professor Robert Vautard, of the University of Versailles Saint-Quentin-en-Yvelines, found that annual mean wind speeds have declined by 5 to 15 per cent over almost all continental areas in the northern mid-latitudes from 1979 to 2008, with the steepest decline occurring in Asia, particularly China.
A possible reason for the decline is an increase in surface roughness due to the fast growth of trees in a warming climate and an increase in the number of soaring skyscrapers, but the paper said the precise cause could not be specified.
The data for the study was collected from ever-spinning anemometers from nearly 1,000 weather stations. Although an anemometer is usually located no more than 10 metres off the ground, much lower than a wind turbine, the research warns that if the wind speeds continue to decline, it would lead to a major loss of wind power production. Tang Jianping , an associate professor at Nanjing University’s College of Atmospheric Sciences, said meteorologists on the mainland noticed a long time ago that winds were slowing down. The increase in surface drag caused by urbanisation might explain the slowdown near cities, but it could not explain why monsoon winds from the sea had slowed as well, he said.
The general atmospheric circulation, influenced by global warming, might have been undergoing some fundamental changes, he said.
Wind power might be one of the first things affected when temperatures rise, said Tang, who leads a state-funded research project on climate change’s impact on the wind industry. Climate change would alter not just the speed, but also the geographical distribution of the wind energy.
“It is not unlikely that we build a huge wind farm here and discover a few years later that wind begins to blow elsewhere,” he said. “What causes a change in the wind is still one of the biggest unanswered questions in meteorological science.”
South China Morning Post,
25 November 2010
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