Credit: AP PHOTO

Geophys. Res. Lett. doi:10.1029/2009GL039902 (2009)

The cause of the bush fires that swept across southeastern Australia in February, killing more than 170 people, can be traced back to shifting ocean patterns.

Researchers know that when sea-surface temperatures are cooler than normal in the eastern Indian Ocean, and warmer than usual in the western Indian Ocean, this can result in severe drought in southeastern Australia. Now Wenju Cai of CSIRO in Aspendale, Australia, and his colleagues have linked this ocean anomaly to a heightened risk of fire.

Using data on soil moisture and weather patterns, the researchers found that the Indian Ocean shift preceded 11 of the 21 significant bush fire seasons in Australia since 1950 — including February's fires. These ocean changes have been increasing in number — as might be expected owing to global warming — leading the team to suggest that severe fires could occur more frequently if temperatures continue to rise.