Abstract
Abstract. The relationships between climate, vegetation and fires are a major subject of investigation in the context of climate change. In southern Africa, fire is known to play a crucial role in the existence of grasslands and Mediterranean-type biomes. Microcharcoal-based reconstructions of past fire activity in that region have shown a tight correlation between grass-fueled fires and the precessional cycle, with maximum fire activity during maxima of the climatic precession index. These changes have been interpreted as the result of changes in fuel load in response to precipitation changes in eastern southern Africa. Here we use the general circulation model IPSL_CM5A (Institut Pierre Simon Laplace Climate Model version 5A) and the dynamic vegetation model LPJ-LMfire to investigate the response of climate, vegetation and fire activity to precession changes in southern Africa during marine isotopic stage 4 (74–59 kyr BP). We perform two climatic simulations, for a maximum and minimum of the precession index, and use a statistical downscaling method to increase the spatial resolution of the IPSL_CM5A outputs over southern Africa and perform high-resolution simulations of the vegetation and fire activity. Our results show an anticorrelation between the northern and southern African monsoons in response to precession changes. A decrease of the precession climatic index leads to a precipitation decrease in the summer rainfall area of southern Africa. The drying of climate leads to a decrease of vegetation cover and fire activity. Our results are in qualitative agreement with data and confirm that fire activity in southern Africa during MIS4 is mainly driven by vegetation cover.
Highlights
The relationships between climate, ecosystems and fire are currently a major concern in the context of future climate change, as fire risk is expected to increase in several regions worldwide in response to both the rise in temperature and precipitation decrease (Liu et al, 2010)
We use the general circulation model IPSL_CM5A (Institut Pierre Simon Laplace Climate Model version 5A) and the dynamic vegetation model LPJLMfire to investigate the response of climate, vegetation and fire activity to precession changes in southern Africa during marine isotopic stage 4 (74–59 kyr BP)
The eastern part is under the remote influence of the Intertropical Convergence Zone (ITCZ) and precipitation occurs during austral summer (November–March), when the ITCZ is at its southernmost position
Summary
The relationships between climate, ecosystems and fire are currently a major concern in the context of future climate change, as fire risk is expected to increase in several regions worldwide in response to both the rise in temperature and precipitation decrease (Liu et al, 2010). The studies on this issue are usually based on predicted temperature and precipitation changes only (Liu et al, 2010) They do not take into account possible shifts in the ecosystems, which would change the amount of fuel available or its composition, such as the ratio from coarse fuels to fine fuels and the flammability of fuel components, which in turn will affect fire intensity and frequency (e.g., Daniau et al, 2007). Simulations performed by Bond et al (2003a, b) with a dynamic vegetation model including a fire module are consistent with these field experiments In their simulations, forests cover the eastern part of southern Africa if fire disturbance is not taken into account
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