Fire history and the global carbon budget: a 1°× 1° fire history reconstruction for the 20th century

Abstract

A yearly global fire history is a prerequisite for quantifying the contribution of previous fires to the past and present global carbon budget. Vegetation fires can have both direct (combustion) and long-term indirect effects on the carbon cycle. Every fire influences the ecosystem carbon budget for many years, as a consequence of internal reorganization, decomposition of dead biomass, and regrowth. We used a two-step process to estimate these effects. First we synthesized the available data available for the 1980s or 1990s to produce a global fire map. For regions with no data, we developed estimates based on vegetation type and history. Second, we then worked backwards to reconstruct the fire history. This reconstruction was based on published data when available. Where it was not, we extrapolated from land use practices, qualitative reports and local studies, such as tree ring analysis. The resulting product is intended as a first approximation for questions about consequences of historical changes in fire for the global carbon budget. We estimate that an average of 608 Mha yr À1 burned (not including agricultural fires) at the end of the 20th century. 86% of this occurred in tropical savannas. Fires in forests with higher carbon stocks consumed 70.7 Mha yr À1 at the beginning of the century, mostly in the boreal and temperate forests of the Northern Hemisphere. This decreased to 15.2 Mha yr À1 in the 1960s as a consequence of fire suppression policies and the development of efficient fire fighting equipment. Since then, fires in temperate and boreal forests have decreased to 11.2 Mha yr À1 . At the same time, burned areas increased exponentially in tropical forests, reaching 54 Mha yr À1 in the 1990s, reflecting the use of fire in deforestation for expansion of agriculture. There is some evidence for an increase in area burned in temperate and boreal forests in the closing years of the 20th century.

Driving forces of global wildfires over the past millennium and the forthcoming century

“…An exception is the first two decades of the century in the western United States, where the historical reconstruction shows increased burning, whereas our model indicates decreased fire activity. Although the historical reconstruction relies on data that are often too inconclusive to support consistent quantitative accuracy (25), it is likely that fire activity in the early 20th century was indeed higher throughout the United States, due to extensive agricultural fires (15,25), which are not depicted by our model. However, the overall correspondence between reconstructed and modeled past fire trends provides reasonable confidence in our future regional estimates in areas where precipitation projections are relatively robust [such as North America, Europe, and Australia (24)].…”

“…Our results indicate a precipitation-driven preindustrial fire regime, shifting to an anthropogenic-driven regime in the 18th century, and an imminent shift to a temperature-driven global fire regime in the future. This suggests a real possibility that fire management policies will have to adapt to a world in which climate plays a substantially stronger role in driving fire trends, (25), which can be qualitatively compared with fire activity. Bar color indicates reconstruction reliability (25)-"accurate" (black), "good" (gray), "poor" (light gray), and "very poor" (white).…”

Climate Feedback on Aerosol Emission and Atmospheric Concentrations

“…Prerequisites for fires are the supply and availability of fuel (biomass) and ignition, which can be natural or humandriven. An example is the strong change in boreal fires in recent decades [24].…”

Ten years of global burned area products from spaceborne remote sensing—A review: Analysis of user needs and recommendations for future developments

“…Tropical regions follow in importance, particularly in central Africa, the Amazon Basin and SE Asia. This inter-tropical region actually represents more than 60% of the burned area globally (Mouillot et al 2005), but most countries in this region do not have operational fire observation systems, and therefore official fire statistics are not very reliable. Additionally, there is a double interest in air chemistry due to the large amount of carbon and aerosols released from these biomes, and a significant demand for forest management and protection from deforestation.…”