Attribution of extreme events in Australia using Weather@Home ANZ

David Karoly, Mitchell Black, Andrew KingSchool of Earth Sciences and ARC Centre of Excellence for Climate System Science,

University of Melbourne

Michael GroseCSIRO, Hobart

Fredi Otto Sue RosierECI, University of Oxford, UK NIWA, NZ

Update on actities in 2015• Real-time attribution of record Oct 2015 month mean Tmax for Australia, state of Victoria and Melbourne -https://theconversation.com/its-been-australias-hottest-ever-october-and-thats-no-coincidence-49941, posted 29 Oct.

• Attribution of record high MSLP in August 2014 south of Australia - Grose, M.R. et al. (2015) Attribution of exceptional mean sea level pressure anomalies south of Australia in August 2014. BAMS, 96(12), S158-162.

• Impact of perturbed physics parameterizations on rainfall uncertainties – very preliminary

Weather@home ANZ experiment• Partnership between ARC Centre of Excellence for Climate

System Science, Oxford University and NIWA (NZ) to run Australia-New Zealand domain

• Uses CORDEX Australasia domain (0.44° resol, 216x145)• Simulations for 2013 with specified SSTs initially• Remove human-caused SST and ghg changes for natural runs• Perturbed initial conditions,

different forcings• Launched 26 Mar 2014,

>40,000 runs distributed,>30,000 years daily data back

Record Oct 2015 monthly mean Tmax

Record Oct 2015 monthly mean Tmax• Use lookup tables of precomputed FAR values from CMIP5

models in Lewis et al (2014) for anthropogenic climate change contribution to breaking previous record Oct Tmax, set in Oct 2014.

• Very likely at least a factor of six increase in likelihood of breaking previous record due to global warming

• Consider role of El Niño using W@H ANZ model simulations for typical El Niño SST pattern, with and without climate change; >4000 yrs typical modern El Niño, >8000 yrs typical El Niño without climate change

• For Australia, under El Niño conditions, climate change has very likely increased the likelihood of setting a new record at least ten times

Record Oct 2015 monthly mean Tmax• Victoria, under El Niño, climate change has very likely increased

the likelihood of setting a new record at least six times• Melbourne, under El Niño, climate change has very likely

increased the likelihood of setting a new record at least six times

Record high monthly MSLP in Aug 2014• Record high observed monthly mean MSLP south of

Australia in August 2014• Use W@H ANZ simulations for 2014, >2700 all forcing

simulations with observed 2014 SST, >5000 NAT simulations

Record high monthly MSLP in Aug 2014

Increase in likelihood of record MSLP very likely by at least 70% due to climate change

Impact of perturbed physics in W@H runs• Weather@Home large ensembles for Europe and ANZ

regions have used perturbed initial conditions only• Coupled model runs using climateprediction.net have shown

substantial impact on climate senstivity and on rainfall from perturbed physics parameters

• New experiment to assess impact of physics params on extreme rainfall in Australia

• 60 different physics param sets, grouped around high, normal and low ENTCOEF, 100 initial conditions ensemble for each param set

• Runs not completed yet

Impact of perturbed physics in W@H runs

~5% increase in mean, ~10% increase in variability of Jan mean NAUST rain for PP

Other plans using W@H ANZ• Complete analysis of attribution of extreme fire danger

events in south-east Australia• Include daily column precip water output to monitor

atmospheric rivers and link to extreme daily rainfall in NZ• Examine causes of record low spring and Oct 2015 rainfall in

Tasmania, including roles of El Niño, SAM, blocking, IOD and climate change

• Assess the role of climate change and El Niño in Australian monsoon variability (Bureau of Meteorology)

• Assess future changes in daily extremes across Australia from near-future climate change projection simulations

Summary• Anthropogenic climate change has very likely increased the

chances of record October Tmax across Australia, Victoria and in Melbourne by at least a factor of ten, six and six, resp.

• Climate change very likely increased the chances of the record Aug 2014 MSLP south of Australia by at least 70%

• Perturbed physics ensemble appears to be important for estimating uncertainties in monthly mean rainfall, analysis continuing!

• Lots more going on, we welcome others interested in analysing the data or running the simulations

Please sign up to W@H ANZhttp://www.climateprediction.net/weatherathome/australia-new-zealand-heat-waves/

ReferencesBlack, M.T., D. J. Karoly and A. D. King (2015) The contribution of

anthropogenic forcing to the Adelaide and Melbourne, Australia heat waves of January 2014. Bull. Am. Met. Soc., 96 (12), S145-148.

Grose, M.R., M.T. Black, J.S. Risbey, and D. J. Karoly (2015) Attribution of exceptional mean sea level pressure anomalies south of Australia in August 2014. Bull. Am. Met. Soc., 96 (12), S158-162.

King, A. D., M.T. Black, D. J. Karoly and M. G. Donat, (2015) Increased likelihood of Brisbane, Australia, G20 heat event due to anthropogenic climate change. Bull. Am. Met. Soc., 96 (12), S141-144.

Lewis, S. C., D. J. Karoly and M. Yu (2014) Quantitative estimates of anthropogenic contributions to extreme Australia- and state-wide monthly, seasonal and annual average temperatures, Aust. Met. Ocean. J., 64, 215-230.