Abstract
Abstract. Changes in fire activity over the last 8000 years are simulated with a global fire model driven by changes in climate and vegetation cover. The changes were separated into those caused through variations in fuel availability, fuel moisture or wind speed, which react differently to changes in climate. Disentangling these controlling factors helps in understanding the overall climate control on fire activity over the Holocene. Globally the burned area is simulated to increase by 2.5% between 8000 and 200 cal yr BP, with larger regional changes compensating nearly evening out on a global scale. Despite the absence of anthropogenic fire ignitions, the simulated trends in fire activity agree reasonably well with continental-scale reconstructions from charcoal records, with the exception of Europe. For some regions the change in fire activity is predominantly controlled through changes in fuel availability (Australia monsoon, Central America tropics/subtropics). For other regions changes in fuel moisture are more important for the overall trend in fire activity (North America, Sub-Saharan Africa, Europe, Asia monsoon). In Sub-Saharan Africa, for example, changes in fuel moisture alone lead to an increase in fire activity between 8000 and 200 cal yr BP, while changes in fuel availability lead to a decrease. Overall, the fuel moisture control is dominating the simulated fire activity for Sub-Saharan Africa. The simulations clearly demonstrate that both changes in fuel availability and changes in fuel moisture are important drivers for the fire activity over the Holocene. Fuel availability and fuel moisture do, however, have different climate controls. As such, observed changes in fire activity cannot be related to single climate parameters such as precipitation or temperature alone. Fire models, as applied in this study, in combination with observational records can help in understanding the climate control on fire activity, which is essential to project future fire activity.
Highlights
Fires appeared on Earth soon after the onset of terrestrial plants and are an integral part of the Earth system (Bowman et al, 2009)
Brücher et al (2014) showed that the simulated climate over the Holocene is characterised for the northern tropics by an intensified and northward-shifted monsoon system which leads to a widespread greening between 8000 and 4000 cal yr BP, in line with previous findings (Claussen, 1997; Brovkin et al, 2002; Prentice et al, 1992)
While in some regions the burned area changes are predominantly controlled via changes in fuel availability (Australia monsoon, Central America tropics/subtropics), others are more strongly impacted via changes in fuel moisture (North America, Europe, Asia monsoon, Sub-Saharan Africa)
Summary
Fires appeared on Earth soon after the onset of terrestrial plants and are an integral part of the Earth system (Bowman et al, 2009). Fires form an important natural disturbance process affecting vegetation distribution and structure (Scheiter and Higgins, 2009). Fires impact the climate through various processes, such as changes in surface properties and emissions of trace gases and aerosols into the atmosphere (Randerson et al, 2006; Ward et al, 2012; Keywood et al, 2013). Fires are controlled by climate (Westerling, 2006; Harrison et al, 2010). An analysis of palaeorecords on fire activity can improve our understanding of the climate control on fire activity, which will be essential to project future fire activity and climate change
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