final_program_abstracts[1]

11 IMSC Session Program
Variations of climate extremes in Australia during 1911-2008
Thursday - Parallel Session 7
Ailie Gallant and David Karoly
University of Melbourne, Australia
A modified version of the Climate Extremes Index (mCEI) of Karl et al. (1996) has
been developed for Australia to identify changes in climate extremes on interannual,
decadal, and longer time scales. The mCEI is based on a suite of non-parametric
indices measuring the spatial extent of the areas experiencing extremes of daily and
annual temperature, rainfall and soil moisture each year from 1911 – 2008. Though
interannual and decadal variability are present, trends showing increases in the extent
of warm temperature extremes and decreases in the extent of cool extremes are
evident over the period of record. There have also been increases in the areas
experiencing extreme numbers of wet days and extreme soil moisture surplus during
this time and some changes to heavy daily precipitation.
The extremes indices used for this study are non-parametric and percentile-based.
This makes it easier to combine indices for different climate variables, such as for
temperature and rainfall. It is also easier to compare indices from observations and
climate model simulations, as changes in the indices are compared to their own
frequency distributions, avoiding some of the problems that climate models may have
in simulating extremes.
The causes of annual to century-long variations of these extremes indices are
investigated. The influence of large-scale natural climate drivers, such as El Niño –
Southern Oscillation (a strong interannual driver of mean Australian rainfall and
temperature) is assessed, as is the contribution from random climate variability. The
influence of anthropogenic forcing on the long-term trends is determined using
comparisons of the observations and coupled climate model simulations from the
CMIP3 multi-model archive. The observed variations in extremes are compared with
those from model simulations for the period 1911-2008 forced by natural forcings
(e.g. solar and volcanic eruptions) and anthropogenic forcings (greenhouse gas and
sulfate aerosols), as well as from control model simulations with no changes in
external forcing. A deviation outside the range given by the control experiments
implies that anthropogenic forcing is likely to have contributed to the trends in
Australian climate extremes from 1911 – 2008.
Abstracts 251