The scale of cropland loss in the region is striking. Over the last forty years, more than four million hectares of farmland have disappeared across the Western United States, retired, converted, or abandoned as drought, water scarcity, and economic pressures reshaped agriculture. Within the specific zones where wildfires and cropland converge, the study found that approximately 10.6 million acres of irrigated land have transitioned to other uses since 1985, an area roughly equivalent to the size of Switzerland. Much of that land has given way to scrubland and other low-lying vegetation that burns more readily than well-watered fields. About twenty percent of the converted acreage was developed into human communities, concentrated around metropolitan areas, introducing new ignition sources and complicating suppression efforts.

To quantify how cropland influences where fires stop, the team assembled an unusually comprehensive dataset: wildfire perimeter records for nearly 10,000 fires spanning 1985 to 2024. By overlaying these perimeters with land-use maps, they could ask a deceptively simple question — when a wildfire reaches a boundary between different land types, where does it tend to halt? The answer was consistent across the region. Compared with wildlands, forests, and urban areas, cropland was significantly less likely to end up inside a burn scar. Across nearly four decades of fire records, cropland was 1.3 to 5 times more strongly associated with where fires stopped than other land types, with only barren land performing as an equally effective fire barrier.

The mechanism behind this buffering effect is rooted in basic fire physics. Actively irrigated crops retain substantial moisture in their tissues and in the soil beneath them, raising the fuel moisture content well above the thresholds at which vegetation ignites and carries flame. Moist fuels absorb heat that would otherwise preheat adjacent material, suppressing the spread of fire across the field boundary. Beyond moisture, the geometry of farmland matters: wide, open expanses of low-stature vegetation lack the vertical continuity that allows flames to climb into shrubs and tree canopies. These open spaces also serve a tactical role during active incidents, offering staging points for firefighters and equipment in landscapes where access can otherwise be dangerously limited.

The buffering effect is strongest where irrigation schedules overlap with fire season, a pattern the researchers observed in some of the West’s most productive agricultural regions: California’s Central Valley, Washington’s Columbia Basin, and Idaho’s Snake River Plain. In these landscapes, peak water application coincides with the hottest, driest months, meaning fields are at their most fire-resistant precisely when the surrounding wildlands are at their most flammable. Satellite imagery from the study makes the pattern visually unmistakable, with irrigated fields appearing as unburned red islands within blackened fire perimeters.

For Gordon, a hydrologist whose work has long focused on agricultural water use, the findings reframed her own discipline. Water researchers tend to concentrate on how much water crops consume and how much can be saved by reducing or changing production in drought-stricken areas, she explained, but far less attention has gone to what happens after the land use changes. Collaborating with wildfire managers made clear that drought adaptation strategies which alter cropland can influence how fire moves through the landscape. In her words, out in the West, there is no longer the luxury of thinking about just one hazard at a time. The study’s central argument is that water conservation and wildfire risk reduction should be managed jointly rather than in isolation.

This matters because the most widely used water-saving strategies are precisely the ones that remove irrigated land from production. Targeted and voluntary idling of cropland is a practical, politically feasible tool for reducing agricultural water demand, and it has been deployed repeatedly during drought emergencies. But the new analysis shows that removing cropland eliminates its fire-buffering advantages regardless of what the land becomes next, whether that is dry scrub, grassland, or suburban development. A field retired to save water in one year may become a corridor for fire spread in the next, and the tradeoff is rarely accounted for in drought planning documents.

The authors argue that existing institutional machinery could be adapted to close this gap. They propose supporting structures that integrate water and wildfire planning, developing methods to evaluate transition-specific water savings against the wildfire risk they create, and using established agricultural conservation programs as planning platforms. One candidate is the U.S. Department of Agriculture’s Conservation Reserve Program, which already offers financial incentives to landowners who convert environmentally sensitive land out of production. Expanding such programs to weigh fire-buffering value alongside their existing criteria, the researchers suggest, would allow policymakers to identify where retiring farmland delivers the greatest water savings at the lowest cost to community fire resilience.

Gordon emphasized that the findings do not admit a simple answer. The complexity cannot be reduced to slogans like fire is bad or cropland is water intensive, she cautioned, expressing hope that the work can help identify where the trade-offs are steepest when communities face compounding hazards. That nuance is essential for a region where every option carries costs: keeping land in production consumes scarce water, retiring it may accelerate fire spread, and converting it to housing places more people and ignition sources in harm’s way. The goal, the researchers suggest, is not to freeze agricultural land use in place but to make each transition with a clear-eyed view of its consequences for both water budgets and fire behavior.

The study is the first analysis of its kind for the Western United States, but its conclusions align with earlier European research on the fire-buffering value of croplands, lending the findings broader credibility. The team now hopes to extend the work by quantifying wildfire risk for different specific types of cropland conversion, distinguishing, for example, between land that reverts to scrub and land that becomes subdivisions. Such refined projections could give Western communities a practical planning tool for a future defined by both less water and larger, more severe wildfires — a future in which every acre of irrigated farmland may matter not only for food and water, but for the fire lines drawn on the map.

Subject of Research: The tradeoffs between drought adaptation through cropland loss and wildfire resilience in the Western United States

Article Title: Wide-scale cropland loss has consequences for wildfire resilience in the American West, new research finds

Article References: Wide-scale cropland loss has consequences for wildfire resilience in the American West, new research finds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: wildfire, cropland, drought, irrigation, American West, water conservation, land use change, fire behavior, Environmental Research Letters, Desert Research Institute, urbanization, fire resilience

The research, led by scientists at the USC Dornsife College of Letters, Arts and Sciences and published in the journal Paleoceanography and Paleoclimatology, reconstructs nearly 240,000 years of lake history from a sediment core drilled from the lakebed. The team found that the enormous lakes of the past were brief departures from the basin’s usual hypersaline state, an extremely salty condition that has dominated the record for the vast majority of the time. Both giant lakes appear to have followed the same pattern: as the regional climate warmed and dried, the water receded, salinity climbed and salt deposits formed on the lakebed. The scientists note that the timing of the older of the two transitions is less precise than the younger one, but the overall trajectory of shrinkage and salinification is consistent across both events.

Corresponding author Rachel So, a recent PhD graduate in Earth sciences at USC Dornsife, compares the long-term record to watching a puddle that remains nearly the same size for an hour, briefly swells into a pond and then shrinks again. Scaled up to the size of the present Great Salt Lake, she explains, that is essentially what the basin looked like across nearly a quarter of a million years. For most of the past 240,000 years the lake stayed roughly the same size, but on two separate occasions it briefly grew to ten times its modern extent. The comparison captures the central finding of the study: the freshwater phases that produced the region’s most spectacular lakes were geologically fleeting interruptions in an otherwise salty story.

Scientists have long known that Lake Bonneville once covered much of western Utah during the last ice age, and its ancient shorelines remain etched into the landscape today, visible as terraces on hillsides far above the modern waterline. But those shorelines provide snapshots rather than a continuous account of how the lake’s size and salinity changed through time. To build a continuous record, the researchers turned to a nearly 400-foot sediment core drilled from the bed of Great Salt Lake in 2000. Its layered sediments preserve an archive stretching back about 236,000 years, spanning multiple glacial cycles and capturing both of the great freshwater episodes in a single, uninterrupted sequence.

The team dated the sediment layers by measuring radioactive decay in minerals, a technique that functions as a kind of geological clock and anchors the record in time. They also analyzed molecules left behind by microorganisms that once lived in the lake. Because the relative abundance of those molecules changes with salinity, their signatures allowed the researchers to broadly gauge whether the water at any given moment was fresh, brackish or extremely salty. Together, the dating and the biomarker analysis turned the core into a chronicle of the lake’s alternating states, revealing two major interruptions in its long hypersaline history.

The first and most recent interruption came between roughly 30,000 and 16,000 years ago, when the lake expanded into Lake Bonneville. The second, an earlier deep lake known from the Little Valley interval, existed roughly 140,000 to 135,000 years ago. Shoreline evidence suggests both lakes approached 1,000 feet in depth, but they were not identical twins. The Little Valley lake may have remained somewhat brackish rather than truly fresh, and it lasted less than half as long as Lake Bonneville. The most recent freshwater phase was therefore both longer and fresher than its older counterpart, a difference that offers clues about how variable the region’s wet episodes can be.

Senior author Sarah Feakins, professor of Earth sciences at USC Dornsife, emphasizes that the core’s span of two and a half glacial cycles is what makes the comparison possible. Because the record captures two complete fresh-to-salty transitions, the researchers can compare the two freshwater events directly, evaluating their durations and their degrees of freshness, and seeing how fragile and fleeting those moments were in the basin’s history. The record also aligns with evidence from elsewhere in the American West: various records from Nevada, California and Arizona show similar wet-to-dry shifts during the same periods, suggesting that Great Salt Lake was responding to climate changes felt across the entire region rather than to purely local conditions.

The mechanism behind the lake’s dramatic swings comes down to a balance between water arriving and water leaving. Feakins explains that during the cooler periods, lower temperatures slowed evaporation while more frequent storms delivered additional water into the basin, allowing Lake Bonneville to fill, as she puts it, one storm at a time. As temperatures rose, the balance reversed: evaporation increased, storms became less frequent, and the lakes dwindled. Their remaining water grew progressively saltier until minerals began to form crystals and settle onto the lakebed, leaving salt deposits that the core still preserves today. Great Salt Lake’s lack of an outlet makes it especially sensitive to this balance, since water leaves the basin mainly through evaporation, so any shift in temperature, precipitation or river flow is registered directly in the lake’s level and salinity.

Modern Great Salt Lake faces pressures its ancient predecessors never encountered. Human water use, mostly for agriculture, reduces the amount of water reaching the lake, while human-caused climate change increases evaporation across the region. Feakins notes that today the climate is warming at an unprecedented rate, and that warming makes the atmosphere thirstier, accelerating evaporative drying from soils and lakes throughout the West. Both researchers caution against misreading the ancient record as reassurance. So warns that people should not use the argument that climate changed naturally in the past, and so the lake shrank, to justify treating shrinking lakes today as normal or purely natural phenomena. The geological record shows what a warming and drying climate can do to a closed basin; it does not excuse the additional human pressures now compounding that vulnerability.

The study is not without limitations, and the researchers are candid about them. Dating precision decreases in the core’s older layers, where margins of error span several thousand years, and dating some of the ancient salt deposits proved especially difficult. Attempts to reconstruct past temperatures were also hampered, because the lake’s high salinity made those results unreliable. Despite these challenges, the sediment core delivers a nearly continuous account of a lake responding to major shifts in the West’s water balance, and it demonstrates with unusual clarity how a vast freshwater lake covering thousands of square miles can give way to salt when the climate warms and dries. As the modern West grapples with a shrinking Great Salt Lake, the basin’s own sediments provide a 240,000-year perspective on just how quickly fresh water can disappear.

Subject of Research: Reconstruction of 240,000 years of salinity and lake-level change at Great Salt Lake, Utah, from sediment core evidence

Article Title: Great Salt Lake’s ancient past reveals how quickly fresh water can disappear

Article References: Great Salt Lake’s ancient past reveals how quickly fresh water can disappear. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Great Salt Lake, Lake Bonneville, paleoclimatology, sediment core, salinity, climate change, USC Dornsife, hypersaline lakes, American West, evaporation, glacial cycles, water resources