New NASA study takes detailed look at increased vegetation growth in Alaska and Canada
After taking a close look at 87,000 satellite images, NASA scientists say the northern parts of Canada and Alaska are getting greener. Shrubs are sprouting in grassy tundra zones and shrubs are growing bigger and denser — changes that could have impacts on regional water, energy and carbon cycles.
The new NASA study adds more detail to previous research that reached similar conclusions and could help inform climate scientists about how the changes will affect global temperatures. The study covered the timespan between 1984 and 2012. The images came from the joint NASA/U.S. Geological Survey Landsat program, which provides the longest continuous space-based record of Earth’s land vegetation in existence.
“It shows the climate impact on vegetation in the high latitudes,” said Jeffrey Masek, a researcher who worked on the study and the Landsat 9 project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
With Landsat 5 and Landsat 7 data, Masek and his colleague Junchang Ju, a remote sensing scientist at Goddard, found that there was extensive greening in the tundra of western Alaska, the northern coast of Canada, and the tundra of Quebec and Labrador.
Northern forests greened in Canada, but tended to decline in Alaska. Overall, the scientists found that 29.4 percent of the region greened up, especially in shrublands and sparsely vegetated areas, while 2.9 percent showed vegetation decline.
“The greening trend was unmistakable,” the researchers wrote in an April 2016 paper in Remote Sensing of Environment.
Previous surveys of the vegetation had taken a big-picture view of the region using coarse-resolution satellite sensors. To get a more detailed picture of the 4.1 million square-mile area, scientists used the Landsat 5 and Landsat 7 satellites.
“We can see more detail with Landsat, and we can see the trend more reliably,” Ju said. With finer-resolution and better calibrated data from Landsat, the researchers were able to mask out areas that burned, or are covered in water, to focus on vegetation changes. The more detailed look – now available to other researchers as well – will also let scientists see if a correlation exists between habitat characteristics and greening or browning trends.
“The resolution with Landsat is drastically improved, it lets you look at the local effects of things like topography, such as in areas where you might have small woodlands or open areas,” Masek said. “You can do detailed studies of how climate impacts vary with geography.”
With the higher resolution Landsat data, the researchers also found a lot of differences within areas – one pixel would be brown, and its neighbors green, noted Ju. “It’s very localized,” he said. “The vegetation is responding to the microclimates. That’s the benefit of using Landsat data, is that we can reveal this spatial variation over very short distances.”
With the large map complete, researchers will focus on these short distances – looking at the smaller scale to see what might control the greening patterns, whether it’s local topography, nearby water sources, or particular types of habitat. They also plan to investigate forested areas, particularly in the greening Quebec.
“One of the big questions is, ‘Will forest biomes migrate with warming climate?’ There hasn’t been much evidence of it to date,” Masek said. “But we can zoom in and see if it’s changing.”