Western Australia Annual Preparedness Briefing Mike Bergin, Regional Director 7 September 2015

Outline Recent and Current conditions –Rainfall and temperatures in 2015 –The El Niño -Southern Oscillation The Climate Outlook Up coming warm season –Bushfire –Tropical Cyclones –Thunderstorms –Heatwave –Flood

WA has been getting wetter

Southwest WA has been getting drier

Annual % area in decile 10(rainfall) – Southwestern Australia

Recent conditions (rainfall) January to April May to August

Western Australia is warming Trend in mean temperature 1910–2014 (°C/decade)

Recent conditions (temperature) May to August maxima May to August minima

Extreme temperatures increasing

2013 in Perspective: Future Projections Observed annual temperature RCP4.5 projected annual temperature

Rainfall deficiencies July 2014 – July 2015October 2012 – July 2015

Understanding El Niño

El Niño temperature impacts Typical winter–spring El Niño maximum temperature

El Niño rainfall impacts Historical rainfall deciles from 12 moderate-strong El Niños Rainfall for December to February Rainfall for September to November

Variability in El Niño impacts Winter and spring rainfall deciles for 1982 El Ni ño Winter and spring rainfall deciles for 1997 El Niño Winter and spring rainfall deciles for 1982 El Niño Winter and spring rainfall deciles for 1997 El Niño

Indian Ocean Dipole (IOD) Negative IODPositive IOD

Indian Ocean dipole Weekly sea surface temperatures week ending 30 August 2015

Usually starts around May or June, peaks between August and October and then decays A positive IOD often results in a decrease of rainfall over parts of Australia Typically little effect on Australian climate during the months from December to April Impacts of Indian Ocean Dipole Mean positive IOD winter- spring rainfall deciles Mean positive IOD and El Niño winter-spring rainfall deciles

Spring temperature outlooks Probability of above median maximum temperature for September to November 2015 Probability of above median minimum temperature for September to November 2015

Spring rainfall outlook September October Probability of above median rainfall for September to November 2015 and the months September and October

Issued September 2015 Bushfire potential

Tropical cyclones Australian region 8–14 tropical cyclones (average 11) 2–7 coastal crossings per year (average 4) Western Australia Average of 5 tropical cyclones 2 coastal crossings 1 of which is Cat 3 or higher Last year: below average number of tropical cyclones average number of landfalls All tropical cyclones reached category 3 or above The tropical cyclone season

Tropical cyclone outlook for WA Strong El Niño so less likely to see first cyclone before Christmas Expect slightly below average number of cyclones (around 4) However still expect 2 coastal impacts One coastal impact cat 3 or higher High impact tropical cyclones can occur in any season 2006/7 season only 3 cyclones but one was TC George TC Olwyn 12 March 2015, NASA

North Australian monsoon Delayed onset in El Niño years –First half of January at Darwin –Later at other locations

Severe thunderstorms Photo by Chris Kent Severe thunderstorms can form at anytime of the season Severe thunderstorms produce any of the following: Hailstones ≥ 2cm diameter Wind gusts ≥ 90km/h Flash flooding Tornadoes

Heatwaves: Increased risk A heatwave is 3 days or more of above normal temperatures. Monitor forecasts available at

Flood risk Widespread major flooding is less likely in El Niño (more likely in La Niña) Floods can occur regardless of catchment conditions or climate influences Localised flooding (due to TC's, storms, etc.) are always a possibility Streamflow outlook August to October Soil moisture lower layer (August)

Summary 2015 another warmer than average year despite some cold outbreaks El Niño is a dominant climate driver of weather patterns this season although less of an influence in WA Changes in risk compared to normal warm season Increased risk of heatwaves in warm season Decreased risk of widespread flooding, Localised flood risk remains possibility Increased risk of bushfire in many areas due to dry and warm conditions Severe thunderstorms are ALWAYS possible Slightly later start and slightly below average number of tropical cyclones but still expect 2 coastal impacts in WA