Past Research Projects

Project: Climate Change Impacts on Severe Thunderstorms in Australia

Funding Source: Australian Postgraduate Award

Project Details

The impact of a warming perturbed climate on the occurrence of severe thunderstorms is uncertain, despite the perception of an increasing frequency. Studies for the United States have shown climate models are capable of representing severe thunderstorm environments with limitations, and prior to my research the influence of a warming climate on severe thunderstorm environments in Australia had received little attention, confined to regional modeling studies.
Assessing how climate models reproduce the past climatology of severe thunderstorm environments is necessary before considering a warming climate. In Allen etal. (2014a) I outlined a novel approach to evaluate the performance of climate models in representing convective parameters, and applied this approach to two climate models (CSIRO Mk3.6 and the Cubic-Conformal Atmospheric Model or CCAM) for the period 1980-2000 using a reanalysis climatology and observations as a baseline. This demonstrated the sensitivity to both model physics, relating to moisture and convective parameterizations, and domain size, in how severe thunderstorm environments could be represented. CSIRO Mk3.6 particularly appeared to struggle with timing the diurnal cycle of occurrence, and, in each aspect CCAM was found to be conservative but offer a more accurate representation of the actual climatology.
Taking into account the model limitations, in Allen et al. (2014b) I explored future projections under highly warmed future climate scenarios. In a warming climate, severe thunderstorm environments increased in frequency, particularly over the east coast. Statistically significant increases in occurrence for Brisbane, Sydney and Melbourne were 15%, 30% and 22% respectively of 20th century values. Changes were found to be model sensitive, but in both cases proximity to higher sea-surface temperatures and advected moisture increased the frequency of high CAPE environments in a warmed world. In contrast, high S06 frequency decreased with poleward shift of the jet stream, but did not outweigh the contribution of increases to the thermodynamic energy available to the atmosphere. These results are consistent with recently published findings for the CMIP5 models for the United States, and regional studies for Australia.

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Publications