The warm and extremely dry spring in 2015 in Tasmania contained the fingerprint of human influence on the climate
Michael R. Grose A E , Mitchell T. Black B , Guomin Wang B , Andrew D. King C , Pandora Hope B and David J. Karoly D
+ Author Affiliations
- Author Affiliations
A CSIRO Marine Laboratories, Castray Esplanade, Hobart, Tas. 7000, Australia.
B Research and Development, Bureau of Meteorology, Melbourne, Vic., Australia.
C School of Earth Sciences and ARC Centre of Excellence for Climate System Science, University of Melbourne, Melbourne, Vic., Australia.
D CSIRO Oceans and Atmosphere, Aspendale, Vic., Australia.
E Corresponding author. Email: michael.grose@csiro.au
Journal of Southern Hemisphere Earth Systems Science 69(1) 183-195 https://doi.org/10.1071/ES19011
Submitted: 13 June 2017 Accepted: 26 July 2019 Published: 11 June 2020
Journal Compilation © BoM 2019 Open Access CC BY-NC-ND
Abstract
Tasmania saw a warm and very dry spring and summer in 2015–16, including a record dry October, which had significant, wide-ranging impacts. A previous study using two probabilistic event-attribution techniques found a small but statistically significant increase in the likelihood of the record dry October due to anthropogenic influence. Given the human signal was less clear amid natural variability for rainfall compared to temperature extremes, here we provided further evidence and context for this finding. An additional attribution method supported the October rainfall finding, and the median attributable risk to human influence in the three methods was ~25%, 48% and 75%. The results suggested that human influence on rainfall was partly through increased sea level pressure in the mid-latitudes associated with fewer rain-bearing systems, a circulation driver that was consistent with recent trends that have been attributed to human influence. Dry conditions were also driven by a positive Indian Ocean Dipole and El Niño at the time, but this study could not reliably estimate the effect of human influence on these phenomena, as each model gave a different estimate of the ocean warming pattern. Along with rainfall, attribution modelling showed a role for human influence in higher temperature and evaporation through October 2015, as well as a high drought index throughout spring. Confidence in the attribution of a human signal on this extreme dry event increased as multiple attribution methods agreed, a plausible atmospheric circulation driver was identified, and temperature and evaporation also showed an anthropogenic signal.
Additional keywords: Australia, circulation, event attribution, rainfall extremes.
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