Wind resources have been unquestionably low in much of North America – so low that the possibility of a prolonged ‘wind drought’ has been on the minds of many in the wind industry. Will such a phenomenon happen again in 2016?
Unfortunately, there are not many tools for forecasting weather conditions more than a few weeks into the future – and all carry a lot of uncertainty.
One approach is to examine so-called teleconnections relating events such as El Nino to weather conditions in areas of interest. They can be useful for long-range forecasts because many organizations forecast El Nino – and also because El Nino is linked to sea-surface temperatures, which are relatively slow to change and, hence, more easily forecast.
If the relationship between El Nino (and other climate cycles) and wind resources can be understood, then, perhaps, there can be something meaningful to suggest about wind conditions in the future.
That there is a relationship between El Nino and wind resources is clear enough. The global maps below show the correlation between the average wind speed anomaly and a leading index depicting El Nino/Southern Oscillation (ENSO).
The maps depict a multivariate ENSO index for the months of January-February, April-May, July-August and October-November for 1988-2014. Depending on how El Nino is defined, this period spans about seven or eight El Nino events.
The red colors indicate areas where winds tend to be lower when the ENSO index is positive – meaning El Nino. This is the case over most of North America in winter and spring. The reason has to do with the path of storms, which tends to be farther south when El Nino is present, bringing rainfall to the southern U.S. and Mexico.
During La Nina, storms follow a more northerly track, bringing stronger winds to much of the rest of the continent. El Nino has noticeably less influence in summer and fall.
Now we can combine this information with the ENSO forecasts. The chart below shows an ensemble of forecasts of the equatorial sea-surface temperature anomaly in the eastern Pacific – a key signature of El Nino. The periods are three-month rolling averages; NDJ is November-December-January, for example. Almost all models suggest that the present El Nino will persist through late spring and early summer of 2016.
We took this information and asked a simple question: For periods when the MEI has been above 0.75, what was the average wind speed anomaly? The maps below show the answer for North America.
The result, unfortunately, is a little discouraging. If the average historical pattern holds, average wind speeds will be around 3% to 6% below average in the U.S. this coming winter and spring.
Of course, the average historical pattern may not hold – a problem with seasonal weather forecasts. There have been times when winter and spring winds were near or above normal during El Nino episodes. Moreover, El Nino may fade more rapidly than forecast, making the spring outlook especially uncertain.
Still, based on what we know right now, I wouldn't bet on winds being above normal in the first few months of 2016.
Michael Brower is president and chief technical officer of Albany, N.Y.-based AWS Truepower. He can be reached at michael.brower@awstruepower.com. This article was excerpted with permission from AWS Truepower. To read the full blog post, "The North American "Wind Drought': Is it the new normal?" click here.
