Months after wildfires eliminate vegetation that holds hillside sediment together, debris flows—destructive landslides that carry bulky material down once-stable slopes—can devastate infrastructure, taking out roads and buildings in their wake.

Though the U.S. Geological Survey (USGS) creates hazard predictions used to warn communities of the risk of these postfire debris flows, those predictions haven’t fully considered how recovering vegetation reduces risk over time—until now.

A new study published in Geosphere presents a new way to calculate postfire debris flow risk that takes vegetation recovery into account. The USGS will begin using the new method this wildfire season to create more accurate maps of debris flow hazard in the years after a fire.

“I’m so appreciative that the focus on how the debris flow hazard changes over time after fire is being addressed,” said Nancy Calhoun, a geologist and postwildfire debris flow program manager at the Washington Geological Survey who was not involved in the new study. Calhoun said she relies on the USGS hazard assessments for virtually everything her job requires.

“We’re glad to have a way that we can help our partners moderate those situations where the hazard has decreased,” said Andrew Graber, a geologist at the USGS Landslide Hazards Program and lead author of the new study.

Assessing Hazard, Again

After a wildfire, the USGS creates hazard maps that incorporate information about soil type, steepness, and burn severity (how much vegetation has been lost) to show where the risk of a debris flow may be elevated.

Then, the agency distributes this guidance to the National Weather Service, which uses it to set rainfall thresholds: levels of rainfall at which a debris flow becomes likely. State, county, and city agencies use those rainfall thresholds to issue warnings or take action when rainfall is imminent, for example, by closing highways or triggering evacuations.

The methods used to create the USGS maps, however, historically relied on a snapshot of the burned area taken just after the fire, and the maps weren’t updated to reflect conditions as vegetation grew back and began holding soil in place again.

That led to situations where public safety decisions were made on the basis of outdated maps and rainfall thresholds. For example, concern over debris flows after the 2020 Grizzly Creek Fire in Colorado led to several closures of Interstate 70 in 2022, but the debris flows never happened.

“What [the original assessments] didn’t capture is how the vegetation came back,” Graber said. “That left us with some uncertainty when we started to get further away in time from the fire.”

To test an improved method for these hazard assessments, Graber and the research team incorporated satellite imagery of 12 burned areas that showed the degree of vegetation recovery right after the fire, 1 year after the fire, and 2 years after the fire. Then, they tested their new method by comparing its predictions to rainfall and debris flow data from the 12 burned areas.

The updated method better reflected what had actually happened after the fires, reducing the number of unnecessary warnings without missing real-world debris flows.

Risk Recalibration

The USGS plans to begin using their new workflow to create hazard maps for some higher-profile fires during the coming wildfire season.

That’s exciting for Calhoun. As part of her job, she’s in constant contact with emergency managers who periodically ask how worried they should be about debris flows in areas that burned years ago. “It’s a really important question: Are we still worried about this burn scar?” she said.

Right now, Calhoun has no data to point to in the years after a fire to give an updated answer to that question. Using the new method from Graber and the research team, she will.

“Because they’re using satellite [imagery] and repeatable quantitative methods to look at these burn scars over time, we’ll actually be able to say something useful and informed about vegetation recovery,” she said.

Having a deeper understanding of how debris flow risk evolves over time is especially important because debris flows themselves are becoming a greater risk to the public as a result of increasingly intense wildfires and rainstorms. In addition, more accurate assessments can reduce warning fatigue, which occurs when too many false alarms lead to people ignoring or opting out of alerts.

Graber hopes he and the USGS will continue to improve their methods for assessing debris flow hazards by collecting more debris flow data across the country and improving the underlying equation for hazard assessments so that it better reflects the unique conditions of different ecosystems in the United States. USGS researchers also published a new study in March presenting a method to generate maps of where debris flows might travel if they do occur.

“It’s a big year for USGS’s useful postfire products,” Calhoun said.

—Grace van Deelen (@gvd.bsky.social), Staff Writer

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Citation: van Deelen, G. (2026), A new approach can better predict debris flow hazards years after fires, Eos, 107, https://doi.org/10.1029/2026EO260160. Published on 19 May 2026.

Text © 2026. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Lead-acid batteries are omnipresent. An integral part of most electric vehicles and all conventional vehicles globally, they also serve as backup energy storage systems in developing countries. But if lead-acid batteries are recycled in smelting units without adequate pollution control measures, they can cause elevated lead pollution that persists in local soils for thousands of years. However, because recycling sites with pollution control measures cost millions of dollars, most efforts are informal and unregulated.

In a recent study, researchers reported that scraping lead-contaminated soil in the vicinity of an abandoned recycling site for used lead-acid batteries and treating it with phosphate was linked to a 22% reduction in the blood lead levels (BLLs) of children who were living close to that site in a Bangladeshi town. The research was published in the International Journal of Hygiene and Environmental Health.

“Informal battery recycling is rampant in Bangladesh,” said study coauthor Mahbubur Rahman, an environmental health scientist at the International Centre for Diarrhoeal Disease Research, Bangladesh. “Used lead-acid batteries are broken up and smelted in close proximity to residential and agricultural areas, which exposes those communities to lead emissions that contaminate their soil and water sources.”

Rahman and colleagues analyzed the BLLs of 130 children living close to two recycling sites for used lead-acid batteries (ULAB) in the Tangail District of Bangladesh that were abandoned in early 2019. They also assessed the BLLs of 37 children who did not live anywhere near ULAB recycling sites. The researchers then carried out soil remediation efforts at one of the ULAB sites but not the other. Prior to the work, the team members held informational sessions for the community about the dangers of lead pollution so locals could provide informed consent to participate.

The team observed that following remediation efforts, the lead content of the soil in and around the former battery recycling site decreased from more than 20,000 parts per million to less than 400 parts per million, which was considered acceptable by the U.S. EPA when the study was conducted, from 2022 to 2023. (The EPA reduced the limit to 200 parts per million in 2024.)

The researchers collected and cleaned up soil from children’s play areas, roadsides, and courtyards of 68 households that belonged to the intervention group. A year after the lead-contaminated soil was cleaned up, the 89 children from those households had the most significant decreases in their BLLs: from 90.1 to 70.4 micrograms per liter, a decrease of more than 21%.

The children in the group who lived close to the second abandoned ULAB recycling site, where soil remediation was not conducted, experienced only about an 8.4% decrease in their BLLs, from 88.5 to 81.1 micrograms per liter. The reduction in the control group’s BLLs could be attributed to a government initiative focused on reducing lead levels in turmeric, which was happening over the same time period as the study, Rahman said.

Anne Riederer, an environmental health scientist at the University of Washington who was not involved in the new study, said the dangers of lead exposure from ULAB recycling sites are well documented.

“We know for sure that the areas close to abandoned ULAB recycling sites are as contaminated as areas around abandoned lead mines. This study fits with the bigger picture of what we have learned to date about cleaning up contaminated sites and how that could improve children’s health,” she said.

A Widespread Issue

Similar studies conducted in Brazil and Bangladesh reported 46% and 35% reductions, respectively, in children’s BLLs following soil remediation initiatives around ULAB recycling sites.

Despite those drastic improvements, the children’s BLLs were still far above the World Health Organization’s threshold of 50 micrograms per liter. “This could mean there are other sources of lead exposure, like paints and cookware items,” said Rahman. “Or the persistently high BLLs could be because of chronic and long-term lead exposure, due to which lead gets deposited deep into the bones for several decades, even if [people] move away from toxic sites.”

“The reason why this issue is so widespread is [that] informal recycling is cheap,” he said. “That makes the formal sector reluctant to invest in costly pollution control measures.”

—Anuradha Varanasi, Science Writer

Citation: Varanasi, A. (2026), Cleanup of battery recycling sites may lower childhood lead exposure, Eos, 107, https://doi.org/10.1029/2026EO260120. Published on 15 April 2026.

Text © 2026. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.