The grasslands of the Great Plains have seen one of the sharpest increases in large and dangerous wildfires in the past three decades, with their numbers more than tripling between 1985 and 2014, according to new research.

The study, published in the journal Geophysical Research Letters, found that the average number of large Great Plains wildfires each year grew from 33 to 117 over that time period, even as the area of land burned in these wildfires increased by 400 percent.

This is undocumented and unexpected for this region, said Victoria Donovan, the lead author of the study and a researcher at the University of Nebraska-Lincoln. Most studies do document these shifts in large wildfires in forested areas, and this is one of the first that documents a shift, at this scale, in an area characterized as a grassland.

Donovan published the study with two university colleagues. The research looked at large wildfires, defined as fires about 1,000 acres or more in size.

In other parts of the globe, such as Africas savannas, grassland fires are extremely common and that used to be true for the Great Plains as well. But in the past century or more, Donovan said, wildfire suppression techniques such as rapidly catching fires and putting them out had largely eradicated them from the region.

However, theyve begun to come back, a trend that has been consistent not only with climate change but also an incursion of more invasive plant species that could be providing additional fuel, Donovan said. However, the study merely documented the trend toward increased large wildfires without formally attributing its cause.

The year 2011 saw a particularly large surge of Great Plains wildfires, which accounted for half of the total acreage burned in the United States that year.

By specific region, some of the largest wildfire increases occurred in the Cross Timbers region of Texas and Oklahoma (which saw a 2,200 percent increase in the total area burned), the Edwards Plateau of Texas (a 3,300 percent increase), and the Central Irregular Plains, encompassing parts of Iowa and northern Missouri, as well as parts of Kansas and Oklahoma (1,400 percent increase).

Guido van der Werf, a scientist at VU Amsterdam who studies global forest fires and was not involved with the current study, said it was difficult to attribute causes behind the recent uptick in burning.

These grassland fires are somewhat different than the forest fires we are probably more used to, and follow-up research is needed to better understand what the drivers of the upward trends were, he said by email. Agricultural abandonment could be one, wetter conditions later in the record another one (leading to higher and more continuous fuel beds), climate change leading to warmer temperatures, etc.

Max Moritz, a wildfire researcher at the University of California, Berkeley who also was not involved in the study, said the new results are consistent with other work. But he added that he suspects they reflect not so much human-caused climate change but rather changing human behavior.

In particular, he cited a study from earlier this year led by Jennifer Balch of the University of Colorado at Boulder that found that humans were overwhelmingly responsible for lighting U.S. wildfires over the past 20 years (presumably, mostly by accident).

That study shows the Great Plains to have increasing patterns of both lightning- and human-caused fires over this period; yet the vast majority here are caused by humans, he wrote in an email. This suggests that the trends in question may largely be due to shifts in the amount, type, and timing of human activities.

For some time, wildfire researchers have worried about the growth of what they call the wildland-urban interface, in which more and more people are living in proximity to areas conducive to burning.

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UNL researchers find 400 percent spike in wildfire destruction in Great Plains - Omaha World-Herald