Drought and Wildland Fires

This depiction of linear trends in the Palmer Drought Severity Index from 1948 to 2002 shows drying (reds and pinks) across much of Canada, Europe, Asia, and Africa and moistening (green) across parts of the United States, Argentina, Scandinavia, and western Australia. (Illustration courtesy Aiguo Dai, NCAR, and the American Meteorological Society.) Water has been labeled the environmental issue of the 21st century. When reliable rainfall disappears from a region for years or even decades, the impacts on plants, animals, and people can be profound.

Many of the world's droughts are steered and shaped by large-scale climate cycles, such as El Niño and La Niña. Through exhaustive analyses, NCAR scientists have helped pinpoint how these cycles can produce drought at far-flung locations. Case studies show the value of prompt drought predictions when societies can relay the information to farmers, policy makers, and other key people.

As the global climate warms, how will that affect the location and duration of droughts? Globally, the average amount of rainfall is expected to increase, as the warmer temperatures lead to more evaporation of water from the sea. However, the same warmth will help dry out land more quickly, so the droughts that do occur may increase in intensity. The percentage of Earth's land area stricken by serious drought more than doubled from the 1970s to the early 2000s.

Computer-based simulations by NCAR scientists and their colleagues have been used to track areas of persistent dryness in the climates of the past and to project where these areas might develop in the future. These models do not yet agree on which specific areas will be most at risk for drought. However, the models tend to produce drying in the hearts of midlatitude continents, such as the central United States, eastern Europe, and western Asia. Southern Australia—already in a severe multiyear drought—is at enhanced risk for further drying, as the storm track encircling Antarctica shifts poleward.

Where drought does strike, the risk of wildland fire soars. NCAR takes a multidisciplinary approach to address this concern. Fine-scale models have simulated the erratic behavior of a fast-moving wildland fire. Mobile radars have sampled the hot, gusty winds of wildfires at close range. And atmospheric chemists have measured mercury and other environmental hazards in the witch's brew of smoke and gas spewed from a raging wildland blaze. A blend of satellite data and modeling revealed that wildfires in Alaska and Canada in 2004 emitted about as much carbon monoxide as did human-related activities in the continental United States during the same period. The fires also increased ground-level ozone across much of the Northern Hemisphere.

Wildland fires are part of a feedback loop that relates to global climate change. When trees and grasses burn, they release carbon dioxide, thus adding to the greenhouse effect and raising the risk of future heat-stoked wildfires.

Research at NCAR and elsewhere shows that the policy of suppressing fires over the past century has locked up about 25% of Earth's carbon budget in forest vegetation. If more forests burn, whether from wildfires or increased prescribed burning, more carbon dioxide will be released back into the atmosphere, where it will join the increased emissions from vehicles and industry.