Climate of Australia

Ian Rutherfurd

World rainfall

• Global Position• Topography

This lecture …

1. Context of Australia

2. Summary of climate

3. Aridity

4. Present climate pattern

5. ENSO

Two climatic zones

• Tropics = 40% = north of  Tropic of Capricorn, a “wet” or summer season and a “dry” or winter season.

• Temperate = 60% = four distinct (4) seasons = spring, summer, winter and autumn

• Transition zone

General controls on Australian climate:

Aridity(33% arid, 75% semi-arid1 million km2 of sandplain)

• Global position

• Flat

Northward drift: 50 – 60 m.y.

• Aridity began 10 - 17 m.y.• Growth of west Antarctic Ice sheet• Circumpolar current developed (cooler

water)• Decreased penetration of cool, moist air• Desert dunes in place 0.3 m.y.• Western palaeochannels dry 0.5m.y.• Peak of aridity about 20 - 30,000 BP

Origins of aridity

Circum-polar current

Flat• Murray falls 100m from Albury 2200 km

from sea

• Mean height = 300m

• World average = 700m

Consequences of aridity …

• Landforms

• Vegetation

• Animals

Palaeo-drainage lines of

WA

Linear Dunefields

Absence of Glaciation!

• Ice sheets 3 km thick in N.Hemisphere

• Australia too low

• < 0.5% glaciated in Pleistocene (much of Tas, but only 50 km2 mainland)

Glaciation

Tropical/monsoonal Australia

Monsoon• Monsoon = a seasonal reversal of wind

direction.

• Dry winter (April – Nov)

• Wet summer (Oct – March)

Cyclones reach the north west in November to April and the north east in January to April

Temperate Australia

• Mediterranean climate

• Winter = Succession of fronts from SW

• Summer = dry air from central low pressure system

Cold Fronts

• subtropical high pressure cells passing from west to east.

• These normally associated with stable conditions, clear skies and low rainfall.

• Cold fronts between cells

Decadal fluctuations = El Nino

• Droughts in Australia every few decades

• Australia's most costly natural hazard primarily because it causes lost agricultural production

• The 1994/95 drought = 47% reduction in farm production, a US$2000 million or 0.75% drop in GDP, increased unemployment in sections of rural Australia and a 9% reduction in rural exports

El NinoWinter

Decadal flow oscillations:Floods droughts and El

Nino Southern Oscillation• Correlation between floods/droughts

and sea-surface temperatures in the Eastern Pacific (eg. Peru)

• Warm current Eastern Pacific = Floods in Peru = drought in Australia + failure of monsoon

Floods droughts and El Nino Southern Oscillation

This month SOI = 7.7

• Global Position• Topography

• Arid• Position + Flat• Tropical/monsoonal• Temperate