Article Type:
Research Article

Changes in the Risk of Cool-Season Tornadoes over Southern Australia due to Model Projections of Anthropogenic Warming

B. Timbal Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia

Search for other papers by B. Timbal in
Current site
Google Scholar
PubMed Close
,
R. Kounkou Météo-France, Paris, France

Search for other papers by R. Kounkou in
Current site
Google Scholar
PubMed Close
, and
G. A. Mills Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Victoria, Australia

Search for other papers by G. A. Mills in
Current site
Google Scholar
PubMed Close
Print Publication:
01 May 2010
DOI:
https://doi.org/10.1175/2009JCLI3456.1
Page(s):
2440–2449
Restricted access

Abstract

Anthropogenic climate change is likely to be felt most acutely through changes in the frequency of extreme meteorological events. However, quantifying the impact of climate change on these events is a challenge because the core of the climate change science relies on general circulation models to detail future climate projections, and many of these extreme events occur on small scales that are not resolved by climate models. This note describes an attempt to infer the impact of climate change on one particular type of extreme meteorological event—the cool-season tornadoes of southern Australia. The Australian Bureau of Meteorology predicts threat areas for cool-season tornadoes using fine-resolution numerical weather prediction model output to define areas where the buoyancy of a near-surface air parcel and the vertical wind shear each exceed specified thresholds. The diagnostic has been successfully adapted to coarser-resolution climate models and applied to simulations of the current climate, as well as future projections of the climate over southern Australia. Simulations of the late twentieth century are used to validate the models’ ability to reproduce the climatology of the risk of cool-season tornado formation by comparing these with similar computations based on historical reanalyses. Model biases are overcome by setting model specific thresholds to define the cool-season tornado risk. The diagnostic, applied to simulations of the twenty-first century, is then used to quantify the impact of the projected climate change on cool-season tornado risk. The sign of the response is consistent across all models: a decrease of the risk of formation during the twenty-first century is projected, driven by the thermodynamical response. The thermal response is modulated by the dynamical response, which varies between models. The projected decrease in tornadoes risk during the cool season is consistent with the projection of positive southern annular mode trends and the known influence of this mode of variability on interannual to intraseasonal time-scale variations in cool-season tornado occurrence.

Corresponding author address: B. Timbal, GPO Box 1289, Melbourne 3001, Australia. Email: b.timbal@bom.gov.au

Abstract

Anthropogenic climate change is likely to be felt most acutely through changes in the frequency of extreme meteorological events. However, quantifying the impact of climate change on these events is a challenge because the core of the climate change science relies on general circulation models to detail future climate projections, and many of these extreme events occur on small scales that are not resolved by climate models. This note describes an attempt to infer the impact of climate change on one particular type of extreme meteorological event—the cool-season tornadoes of southern Australia. The Australian Bureau of Meteorology predicts threat areas for cool-season tornadoes using fine-resolution numerical weather prediction model output to define areas where the buoyancy of a near-surface air parcel and the vertical wind shear each exceed specified thresholds. The diagnostic has been successfully adapted to coarser-resolution climate models and applied to simulations of the current climate, as well as future projections of the climate over southern Australia. Simulations of the late twentieth century are used to validate the models’ ability to reproduce the climatology of the risk of cool-season tornado formation by comparing these with similar computations based on historical reanalyses. Model biases are overcome by setting model specific thresholds to define the cool-season tornado risk. The diagnostic, applied to simulations of the twenty-first century, is then used to quantify the impact of the projected climate change on cool-season tornado risk. The sign of the response is consistent across all models: a decrease of the risk of formation during the twenty-first century is projected, driven by the thermodynamical response. The thermal response is modulated by the dynamical response, which varies between models. The projected decrease in tornadoes risk during the cool season is consistent with the projection of positive southern annular mode trends and the known influence of this mode of variability on interannual to intraseasonal time-scale variations in cool-season tornado occurrence.

Corresponding author address: B. Timbal, GPO Box 1289, Melbourne 3001, Australia. Email: b.timbal@bom.gov.au

Save
Cover Journal of Climate
Journal of Climate

  • Canadell, J. G., and Coauthors, 2007: Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks. Proc. Natl. Acad. Sci. USA, 104 , 18866–18870.

    • Search Google Scholar
    • Export Citation

  • CSIRO and Bureau of Meteorology, 2007: Climate change in Australia. Australian Greenhouse Office Tech. Rep., 148 pp. [Available online at http://www.climatechangeinaustralia.gov.au].

    • Search Google Scholar
    • Export Citation

  • Deffenbaugh, N. S., R. J. Trapp, and H. E. Brooks, 2008: Does global warming influence tornado activity? Eos, Trans. Amer. Geophys. Union, 89 , 553–554.

    • Search Google Scholar
    • Export Citation

  • Hanstrum, B. N., G. A. Mills, A. Watson, J. P. Monteverdi, and C. A. Doswell, 2002: The cool-season tornadoes of California and Southern Australia. Wea. Forecasting, 17 , 705–722.

    • Search Google Scholar
    • Export Citation

  • Hendon, H. H., D. W. J. Thompson, and M. C. Wheeler, 2007: Australian rainfall and surface temperature variations associated with the Southern Hemisphere annular mode. J. Climate, 20 , 2452–2467.

    • Search Google Scholar
    • Export Citation

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437–471.

  • Kounkou, R., G. A. Mills, and B. Timbal, 2009: A reanalysis climatology of cool season tornado environments over southern Australia. Int. J. Climatol., 29 , 2079–2090. doi:10.1002/joc.1856.

    • Search Google Scholar
    • Export Citation

  • Miller, R. L., G. A. Schmidt, and D. T. Shindell, 2006: Forced annular variations in the 20th century Intergovernmental Panel on Climate Change Fourth Assessment Report models. J. Geophys. Res., 111 , D18101. doi:10.1029/2005JD006323.

    • Search Google Scholar
    • Export Citation

  • Mills, G. A., 2004: Verification of operational cool-season tornado threat-area forecasts from mesoscale NWP and a probabilistic forecast product. Aust. Meteor. Mag., 53 , 269–277.

    • Search Google Scholar
    • Export Citation

  • Perkins, S. E., A. J. Pitman, N. J. Holbrook, and J. McAneney, 2007: Evaluation of the AR4 climate models’ simulated daily maximum temperature, minimum temperature, and precipitation over Australia using probability density functions. J. Climate, 20 , 4356–4376.

    • Search Google Scholar
    • Export Citation

  • Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. Averyt, M. Tignor, and H. L. Miller, Eds. 2007: Climate Change 2007: The Physical Science Basis, Cambridge University Press, 996 pp.

  • Uppala, S. M., and Coauthors, 2005: The ERA-40 Re-Analysis. Quart. J. Roy. Meteor. Soc., 131 , 2961–3012.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 147 47 3
PDF Downloads 93 16 1