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Western Australia Annual Preparedness Briefing
Mike Bergin, Regional Director
7 September 2015
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
-2
-1
0
1
2
3
4
5
1910 1930 1950 1970 1990 2010 2030 2050 2070 2090
Year
Tem
pera
ture
Ano
mal
y
2013 in Perspective: Future Projections
Observed annual temperature
RCP4.5 projected annual temperature
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
Indian Ocean Dipole (IOD)
Negative IOD Positive IOD
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 2014-2015 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
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 http://www.bom.gov.au/australia/heatwave/index.shtml
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
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