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

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1

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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