Global Warming Increases Fire Risk in American West
The steady increase in average temperatures in recent years and the earlier onset of spring-like weather patterns are likely responsible for the increasing number of wildfires in the western United States.
The policy of fire suppression in the forests, which has been widely practiced in the past, plays only a minor role, according to Anthony Westerling of the University of California in San Diego and his colleagues. The ecologists compared the number and extent of wildfires from 1970 to 2003 with climate and land use data for the regions in question - such as the times when the snow melted, the moisture deficit in the vegetation and the spring and summer temperatures of the individual years.
From 1987 there was a significant increase in forest fires: in the following 16 years, there were four times more fires than in the 17 years before. The area burned in each case even increased six and a half times - instead of the rare large fires of short duration (less than a week), extensive fires now frequently occurred, which blazed on average for five weeks. In addition, the annual fire season has since been extended by 78 days and now lasts from March to August. According to the scientists, there is a strong connection between the time of snowmelt and the extent of the scorched areas, since early thawing in particular extends the fire period considerably and enlarges the affected areas - more than half of all large fires took place in these years, and they affected more than seventy percent of the total devastated area.
Particularly affected by the increase were forests in the northern Rocky Mountains, the Sierra Nevada of California, and the Cascade and Coast Mountains of northern California and Oregon. Since all climate models predict further increases in temperatures and thus changes in the length of the seasons, the researchers fear a further increase in the risk of fire in western North America. This is likely to change the composition and density of the forests: current sources of carbon dioxide could therefore develop in the future, which in turn would further fuel the greenhouse effect.
