The world has lost over 2,000,000 square miles of tree cover since 2000—equivalent to the total land area of India and Mexico combined.  Of that total, around 36% is estimated to be permanent deforestation. Much of this forest loss is driven by agriculture, wildfires, and logging. For those in charge of managing our planet’s vast forests, tracking each tree felled is a nearly impossible task. But not catching new logging operations, illegal deforestation, or the onset of forest fires can lead to polluted waters, habitat degradation, and out-of-control blazes. That’s where the global land change monitoring system DIST-ALERT comes in. 

DIST-ALERT provides rapid alerts each time vegetation is disturbed. The idea for a global vegetation monitoring system came from a Satellite Needs Working Group (SNWG) survey highlighting federal agencies' need for frequent, detailed data on land surface changes. To meet this need, Observational Products for End-Users from Remote Sensing Analysis (OPERA) at NASA/Jet Propulsion Laboratory (JPL) partnered with the Global Land Analysis and Discovery (GLAD) lab at University of Maryland to develop the tool. Using DIST-ALERT, land managers can identify when forests—and other vegetated surfaces—change, allowing researchers to spot shifting agricultural patterns, city expansion, and more. 

DIST-ALERT is based on Harmonized Landsat and Sentinel-2 Version 2.0, which combines data from five satellites. Amy Pickens, an assistant research professor at the University of Maryland, developed DIST-ALERT with the other members of the GLAD team using HLS because its global average revisit frequency of observations—every 1.4 days—is ideal for tracking land change. 

Other land change alert systems exist, but DIST-ALERT is unique. The global system has a rolling baseline, allowing researchers to track seasonal changes and disturbances to dynamic ecosystems. Because it's based on HLS data, it also identifies changes earlier than systems based on Landsat or Sentinel-2 data alone, as combining the two datasets maximizes the chances of getting a cloud-free observation.

In the next sections, read more about how land managers are using this innovative new system for decision-making applications.

Identifying Unauthorized Construction

Since 1972, the Clean Water Act has ensured that our nation’s waters are safe for drinking, swimming, and fishing. In New England, staff at the Environmental Protection Agency (EPA)—the agency tasked with enforcing the Clean Water Act—have begun to rely on DIST-ALERT to help identify hidden pollution sources. 

Construction is a major source of water pollution. Because of this, the EPA requires a permit for any construction project that disturbs more than an acre of land near a water body. To obtain a permit, companies must take proper steps to control their environmental impact, including implementing erosion controls to limit the amount of sediment and runoff entering local waterways. Unregulated construction can have a major environmental impact; historically, however, unpermitted sites been extremely difficult to identify. 

That’s where DIST-ALERT comes in. Because New England is heavily forested, most new construction involves cutting down trees, an activity that clearly registers in the DIST-ALERT system. Staff at EPA Region 1, which covers New England, built a dashboard that maps all the permitted construction in the region. When DIST-ALERT flags disturbance in an area without an active permit, EPA staff can conduct a field visit. 

In two recent instances, the EPA team went to investigate potential unpermitted forest clearing identified on the dashboard. They found that one site was a new clearing for a commercial area and the other was an expansion of an existing subdivision. In both cases, the companies behind the construction were able to obtain permits, implement best practices to control pollution, and return to compliance with the Clean Water Act. One of the key strengths of the DIST-ALERT system is that it allows the EPA to intervene early, while the environmental impact is still relatively minor and easy to remedy. That way, the EPA can help companies comply rather than resort to fines or other punitive actions. 

“More than half of site visits identified by DIST-ALERT data resulted in actions to return sites to compliance with the Clean Water Act,” said the EPA Region 1 staff. “The DIST-ALERT data has greatly increased EPA’s ability to monitor Clean Water Act compliance.”

Clarifying Supply Chains

NGIS, a geospatial consultancy, uses DIST-ALERT to help forestry companies in the U.S., Canada, and the EU to better track where their wood is coming from. Most of NGIS’s clients are North American timber companies hoping to sell a portion of their products in EU markets. EU regulation requires that products hit certain sustainability targets, including making sure that wood comes from trees not causing deforestation or degradation of natural forests.

NGIS begins with broad sourcing locations, whose locations are provided by forestry companies like Billerud. Then, they check the DIST-ALERT tool for any changes in those forests over a certain date range, filtering out any wildfires or other natural events to get an up-to-date estimate of where their wood is being sourced.
With DIST-ALERT, U.S. paper or lumber companies can get the precise sourcing location of their wood products and then use ancillary data to prove that their products are in compliance with EU sustainability standards.

A weekly composite of the most recent DIST-ALERT data is hosted on Google Earth Engine, so it can be integrated directly into NGIS’s sustainable sourcing platform. Before DIST-ALERT’s near real-time deforestation alerts, foresters had to wait for annual deforestation maps produced by the forest service or Global Forest Watch.

“[DIST-ALERT] has been a very helpful way for forestry companies to get reliable supply chain information. It saves NGIS time, money, and effort of producing our own weekly forest change detection data. Clients also like data coming from a scientifically credible source with peer reviewed papers backing the data,” said Evan DeLancey, Earth observation scientist at NGIS. 

Protecting Forest Habitat

In Tanzania and Uganda, local communities and protected area rangers are working to monitor and preserve critical chimpanzee habitat. However, the village, district and national forest reserves are large, with some areas like the Tongwe West Local Authority Forest Reserve in Tanzania reaching 1,410 sq miles, and they need help triaging their efforts. In the past, local decisionmakers have used annual forest cover and estimated deforestation maps to create and implement their land use plans, and field monitoring teams have relied on Landsat-based deforestation alerts to identify where new illegal agriculture development or logging is occurring.

However, these alerts don’t always capture forest change fast enough for law enforcement to respond. Sometimes, field teams would learn about a new patch of deforested land in a protected area after those responsible had already moved on.

The Jane Goodall Institute (JGI) is testing out how DIST-ALERT can monitor chimpanzee habitat more regularly to catch disturbances before it’s too late. Thanks to a ROSES-2024 Biodiversity and Ecological Conservation grant led by Dr. Lilian Pintea, JGI is integrating DIST-ALERT into an existing decision support system which helps community forest monitors and protected area rangers decide where to send their field teams to validate what’s happening on the ground. The app is still in pilot phase as they figure out how to best select the most relevant alerts.

“A lot can change on the ground in a couple days,” said Devin Jacobs, GIS Manager at Jane Goodall Institute. “New threats emerge at a pretty quick pace and so we want to make sure that that we have the intelligence about disturbances to the landscape as quickly as possible. DIST-ALERT provides updates on a much more relevant, tangible timeline for field teams, especially as more satellites come on board into the HLS data set.”