What limits fire, where and when: sensitivity of burnt area to different controls
Abstract
Global fire models typically describe fire as a consequence of fuel load, moisture, natural and anthropogenic ignitions, and land use suppression. A lack of information on the temporal and spatial distribution of these controls has meant that their simulated effects on predicting burnt area are largely untested. Despite this, there is a pervasive assumption that burnt area is proportional to the number of ignitions, with many models predicting significant increases in burnt area with human fire starts. Here, we map the limitation and sensitivity of burnt area to each control using a simple framework whereby limitations are imposed by: fuel discontinuity; fuel moisture and atmospheric drying potential; lightning and human ignitions; and land use. Limitations are described from remote sensed and meteorological observations and optimized against Global Fire Emissions Database (GFED4s) burnt area observations. Fuel moisture is shown to be the main limitation of fire over much of the world, (44% annual average and 36% during local dry seasons), particularly in the humid forests and cold, slow drying boreal areas. Fuel discontinuity is the next limitation (25% annually and 23% in the dry season), especially in deserts and dry season grasslands. This is followed by land use change (18% annually, 21 % dry season) and then ignitions (13% annually, 19% dry season), which is only a significant limiting factor in dry season savanna, where rapid drying of fuel built up during the wet season removes all other natural limitations. In these areas, changes in burnt area are actually more sensitive to other controls, typically land use. This study contradicts the way basic processes are represented in many global fire models. As ignitions only impact burnt area over a limited geographic extent, better representation of controls imposed by fuel loads and moisture is vital. Human ignitions only contribute to a small increase in global burnt area (2%), which is offset by the dramatic impact of suppression through anthropogenic land cover changes. The assumption that humans cause burnt area over much of the world is therefore clearly incorrect, and adequate simulation of suppression through land use should become a priority. This result also has implications when considering ecosystem services of agricultural land and fire management policies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGC44B..02K
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3390 Wildland fire model;
- ATMOSPHERIC PROCESSESDE: 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGEDE: 1640 Remote sensing;
- GLOBAL CHANGE