Climate warming seems to have amplified wildfire activity in western U.S. forests over the last 35 years, scientists reported on Thursday.

In recent years, more areas in western U.S. are reporting wildfires that burn hundreds of homes annually and severely damage natural resources. And fire-fighting expenditures by U.S. federal land management agencies now regularly exceed 1 billion dollars per year.

Previous studies have linked these changes with the effects of land-use changes between the 19th and 20th century. But according to a research team led by Anthony Westerling at the Scripps Institution of Oceanography, climate warming should be responsible.

These findings appeared in the July 6 online edition of the journal Science.

Westerling and colleagues compiled a database of 1,166 forest wildfires over 400 hectares in the western U.S. for the period from 1970 to 2003, and compared those data with corresponding measurements of climate, hydrology and land-surface conditions.

They found that wildfire activity increased suddenly in the mid-1980s, with large fires becoming more frequent, fires becoming longer, and the wildfire season also becoming longer.

Since mid-1980s, the researchers found, wildfire frequency was nearly four times the average of 1970-1986, and total area burned by these fires was more than six and a half times its previous level.

The results indicate that fires and hydroclimate, which involves spring and summer temperatures as well as snowmelt, are closely related, and that climate variation has been the primary cause of the increase in fires, although land-use changes can also be important.

These findings have important regional and global implications, the researchers said.

In coming decades, warmer springs and summers will prevail in western U.S., resulting in more early spring snowmelt and longer fire seasons. Thus, large wildfires are expected to occur more frequently, while the region being more vulnerable.

If wildfire trends continue, the researchers said, the burnt forests will in turn become a source of carbon dioxide rather than a natural sink.

"Hence, the projected regional warming and consequent increase in wildfire activity in the western U.S. is likely to magnify the threats to human communities and ecosystems, and significantly increase the management challenges in restoring forests and reducing greenhouse gas emissions," they concluded.

Source: Xinhua