85th AMS Annual Meeting

Thursday, 13 January 2005
Land surface modification by fire of tropical savanna and feedbacks to climate
Nigel J. Tapper, Monash University, Melbourne, Australia, Clayton, Vic, Australia; and J. Beringer, A. Lynch, C. Wendt, and L. B. Hutley
The far north of Australia or the “Top End” as it is commonly known, is characterised by a fire prone woodland savanna landscape. Huge tracts (~250,000km2) of savanna are burnt annually within Australia as a result of both natural and anthropogenic ignitiion.

This study focuses on the physical changes to the savanna landscape caused by fire and the resultant effects of fire scars on boundary layer heating. Albedo values were found to almost halve after fire ranging from 0.12 pre-burn to 0.07 post-burn. In addition there was a fundamental change in energy partitioning, with a reduction in evapotranspiration and an increase in sensible heating to the atmosphere. This wass evident in recorded Bowen ratio (sensible/latent heat flux ratio) values for the pre-burn landscape of 2.5 compared with 6.1 post-burn. The effects of these changes in surface properties and energy partitioning on the boundary layer were measured via vertical profiling of pressure, temperature, relative humidity, wind speed and wind direction, using a tethered balloon and radiosonde. A total of 172 soundings were conducted over burnt and unburnt sites during 24-hour periods over a period of several months. Overall it was found that, when not affected by a local area sea breeze, the burnt site (fire scar) exhibited a warmer (~2 deg C) and drier lower boundary layer. These boundary layer changes resulting from fire scars have the potential to produce mesocale circulations. With individual fire scars throughout the Northern Territory often measuring hundreds of square kilometres and with the total area burned sometimes exceeding 30% of the total land area, the atmospheric impacts at the local to regional scale may become significant.

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