Dec 8, 2010
Climate change may cause winds to falter
Wind farms need to be sited in windy places. Before the turbines go up, companies assess sites carefully to find places where steady winds will keep their turbines turning over the coming decades. But what are the chances of a windy place losing some of its puff?
Brad Griffin and Karen Kohfeld from Simon Fraser University, Canada, and colleagues have shown that climate change can sometimes bring about localized changes such as a drop in wind speed. Such changes can have serious consequences for the people living in that region, and for businesses that rely on particular weather conditions.
The scientists analysed maximum and average daily wind speeds from 92 different wind measurement stations in the Pacific Northwest region of North America, between the years 1950 and 2008. When they separated the coastal stations from those inland, clear trends appeared. Winds at coastal stations were stronger than those inland, and they also appeared to follow an 8–9 year cyclic pattern. Meanwhile, inland sites showed a decline in wind speeds over time of between 0.3 and 0.5% per year.
Neither the cyclic nature of the coastal winds nor the declining wind speeds inland could be explained by any of the obvious climate oscillations, like the El Nino cycle. Instead Kohfeld suspects that a superposition of climate cycles may explain the 8–9-year cycles observed for coastal wind. "We know that the Arctic oscillation has a 2-year cycle and the Pacific North American oscillation has a 1–5-year cycle," explains Kohfeld. "Possibly an interaction between these two climate oscillations is modifying local climate in this region, and controlling the wind speeds."
The declining wind speeds inland could be partially explained by growing urbanization in the region – buildings tend to slow wind – but Kohfeld thinks larger patterns may also be at play. "Declining wind speeds have also been observed over Australia, the mid-continental US and Tibet," she told environmentalresearchweb. "Urbanization is unlikely to explain all of these declines."
Instead, one theory is that the "Hadley Cell" – the global atmospheric circulation system, which controls many of the major wind patterns – may have shifted northwards, bringing lower pressure differences or extensive high-pressure zones and lower wind speeds to mid latitudes around the world. Such changes are predicted by global climate models, and the observed decline in wind speed may be an early indicator that climate change is starting to take effect.
Observing and understanding these localized changes are important when it comes to planning for the future. For example, if air stagnates because of declining wind speeds, atmospheric pollution could take longer to disperse. This might enable pollutants such as ozone to build up, which may generate smog and cause health problems.
And for businesses involved in wind energy, an 8–9-year cycle in coastal wind speeds could make a wind farm unviable. "Many wind turbines have a life span of only two to three decades, in which they must pay for themselves and generate a profit," Griffin and his colleagues write in Geophysical Research Letters. "If power providers conduct feasibility studies during peak times of the wind speed cycle, the amount of power generated over the lifetime of a project may not meet the expectations of owners or utilities requiring electricity. For example, a 3 m/s decrease in the 95th percentile wind speed for coast stations (the change from peak to trough of the cycle) would result in an approximate 49% decrease in power produced."
The scientists have shown that, while global climate models are important for identifying global climate changes, regional and local studies of climate are vital too. "Our study shows that careful downscaling is very important in areas with complex coastlines and mountains," says Kohfeld. As a result the scientists hope to do similar studies and refine the climate picture in other regions too.
About the author
Kate Ravilious is a contributing editor to environmentalresearchweb.