In 2015, satellite images detected a fresh clearing of rainforest in an indigenous reserve deep in the Amazon.

Within months, authorities in Peru had evicted the wildcat miners driving the deforestation, a rare victory in a region where a gold rush has laid waste to large swaths of pristine forest.

The rapid response was possible thanks to better use of satellite technology that now allows deforestation to be tracked in near real-time, giving governments "unprecedented" opportunities to take action, said Matt Finer, the lead author of a paper on the trend in the latest issue of Science.

Instead of years passing before learning about a new deforestation hotspot, authorities can track it in weeks or months, said Finer.

"Most tropical countries now cannot say, 'well we didn't have the information, or we didn't have the information on time'," said Finer, a research specialist at the organization Amazon Conservation, which spotted the 2015 clearing in Peru's Amarakaeri Communal Reserve.

Satellites have gradually been capturing more frequent images of the world's tropical forests with greater detail. In recent years, researchers at the University of Maryland developed an automated early-warning system to notify authorities of likely forest loss, said Finer.

Image: Science

Algorithms can further filter the data by pointing to particularly troublesome patterns, such as the loss of green forest cover inside protected reserves or lines suggesting new roads have been cut through primary rainforest, said Finer.

Daniel Castillo, the head of a team in Peru's environment ministry that uses the technology, said finding out about deforestation early on can keep it from spinning out of control. He pointed to the expansion of illegal gold mining in southern Peru that is now a key driver of the region's economy.

"It's now much more complicated to control," said Castillo. "If we can identify it early, and take corresponding actions, it can be controlled."

The so-called GLAD (Global Land Analysis & Discovery) alerts developed at the University of Maryland now cover more than 20 countries with tropical forest, Finer said.

Peru and Brazil have also developed their own early-warning deforestation systems tailored to their needs, Finer added.

Castillo said his team analyzes deforestation alerts based on Landsat images taken every 8-10 days, and passes worrisome trends on to authorities in other ministries.