The wakes of wind turbines can alter downwind temperatures and humidity, according to a U.S. Geological Survey study, which concluded that the disturbed air downwind can and does impact vegetation in the area.
The study reported that with wind energy expanding rapidly, scientists know little about the impacts on vegetation and surface temperatures of land and sea, and how a small change in verdancy can impact birds and other wildlife.
“We are just beginning to understand how the wakes from wind turbines affect both the terrestrial and offshore environment,” said the U.S. Geological Survey’s research ecologist Jay Diffendorfer. “The next step will be to better understand where and why these effects occur.”
In the study, scientists modeled wake and non-wake zones around 17 wind facilities across the United States, to test if wakes influenced vegetation condition, which was measured using data from USGS’s Landsat satellites. The study was designed to isolate the effects of turbine wakes from other factors that could affect vegetation condition around wind facilities, such as new roads or agriculture.
The wake-induced changes in vegetation condition were found for part or all of the growing season at 10 of the 17 facilities studied.
Researchers found that wakes may have both positive and negative effects on vegetation greenness, a measure that is often used in remote sensing to assess vegetation density and crop health, and that the magnitude of the change in greenness depended primarily on earlier precipitation, the study’ author said. The changes observed at some facilities were consistent with levels that other studies found can affect breeding bird clutch size, species richness, and ungulate (hoofed animal) abundance.
As wind energy expands, understanding where and when wind turbines positively or negatively affect vegetation may aid decisions about where to site wind energy infrastructure. For example, careful placement may benefit agriculture or grazing while minimizing unwanted reductions to the vegetation greenness in the vicinity.
“Wakes induced increased or decreased vegetation greenness at ten of 17 facilities based on BACI ana- lyses, maps of the anomaly in greenness and the difference between expected and observed green- ness in wake zones. While the observed changes in NDVI were relatively small, in some cases the change in greenness were of a magnitude previously docu- mented to affect ecological processes such as clutch size, population abundance, and species richness. The magnitude of wake effects depended primarily on precipitation and to a lesser degree aridity. Future research should advance spatial modelling of pre- dicted wake zones, improve our ability to predict the directionality of the wake impact, and concurrently track microclimate, vegetation, and other ecological variables,” the study concluded.
Global wind energy has expanded 5-fold since 2010 and is expected to expand another 8–10-fold over the next 30 years. With some of the effects on verdancy exceeding 3%, studies such as this one may inform communities and countries as they adopt these so-called green technologies.
The full publication, “Wind turbine wakes can impact down-wind vegetation greenness,” authored by Diffendorfer, is found in the journal Environmental Research Letters.