Insight: Cyclone Monica’s ecological consequences

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Jan 14, 2014

Insight: Cyclone Monica’s ecological consequences

In 2006, a “mega” tropical cyclone (or hurricane) cut a swathe of destruction across northern Australia. Cyclone Monica was one of the largest and most intense such cyclones ever tracked in the southern hemisphere, but because no one died and no towns were hit, it was largely ignored as a major climate event by the wider community. Yet the ecological consequences of this cyclone were profound.

We estimate that Cyclone Monica damaged or destroyed 140 million trees across a million hectares (2.5 million acres) of woodland savanna, the dominant biome of north Australia. This region experiences a wet-dry tropical climate, with a six-month dry season that results in fuel curing. We wanted to examine the impact that the massive increase in fuel load (vegetation debris) following Cyclone Monica would have on the region’s fire regime and resultant greenhouse-gas emissions.

Remote sensing, combined with previously published observations describing the cyclone’s wind field and tree damage extent, enabled us to map the damage zone. We then used remote-sensing data for six years prior to and six years following the cyclone (MODIS gross primary productivity and fire detection data) to discover the following.

  • There was a significant decline in the region’s productivity (directly proportional to its capacity to sequester carbon) relative to pre-cyclone rates, and this reduced productivity persisted for four years post-cyclone.
  • Fire frequencies were extreme in the year following the cyclone, consequently unleashing increased amounts of greenhouse gases into the atmosphere. However, fire frequencies more or less returned to pre-cyclone conditions in the years that followed – an unexpected result.
  • On-ground fuel loads were estimated to potentially release 51.2 Mt of carbon dioxide equivalent, equating to around 10% of Australia’s accountable greenhouse-gas emissions.

Modelling suggests that the frequency of mega-cyclones may increase as a result of climate change, although there is much debate about this. While this trend is not evident in observational data to date, our research highlights the immediate importance of understanding how climate variability and disturbance affects savanna dynamics if landscapes in this region are to be used as enhanced carbon sinks in emission offset schemes.

The team reported their findings as part of the ERL Focus on Extreme Events and the Carbon Cycle.

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About the author

Lindsay Hutley is a lecturer in environmental science at Charles Darwin University School of Environment, Australia. His research focuses on tropical savannas and how vegetation has adapted to the physical environment imposed by a wet-dry tropical climate as experienced in northern Australia. He works on carbon and water cycling in tropical and temperate Eucalypt-dominated ecosystems and, in particular, studies the impact of fire, grazing and weed invasion on these processes.

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