ClimaTea Lecture: "Impact of the ocean warming trend on Australian rainfall extremes during the 2010/11 La Nina event"

Speaker: Dr. Caroline Ummenhofer (WHOI)

Abstract:

Droughts and floods are expected to become more frequent with an intensifying hydrological cycle in a warming world.  Extreme rainfall conditions in Australia during the 2010/11 La Niña resulted in devastating floods claiming 35 lives and billions of dollars in damages and had far-reaching impacts on global climate, including a significant drop in global sea level anomalies, a rare filling of Lake Eyre, and record terrestrial carbon uptake.  Northeast Australian 2010/11 rainfall was amplified by 84% above average conditions, highly unusual even for a strong La Niña event, and soil moisture conditions were unprecedented since 1950.  

We demonstrate that the extreme Australian hydroclimatic conditions that led to destructive floods were significantly exacerbated by – and therefore partially attributable to – a long-term surface ocean warming trend.  Using atmospheric general circulation model experiments with 2010/11 ocean conditions including and excluding a long-term warming trend, we estimate the contribution of sea surface temperature trends in generating this extreme event.  The likelihood of exceptional rainfall in northeast Australia was significantly increased by ocean warming driving enhanced onshore moisture transport onto Australia and anomalous ascent over the eastern half of the continent.  Our results highlight the role of long-term ocean warming containing both natural and anthropogenic signals for intensifying rain-producing atmospheric circulation conditions, increasing the likelihood of extreme precipitation events.