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Climate of Australia. Ian Rutherfurd. World rainfall. Global Position Topography. This lecture …. Context of Australia Summary of climate Aridity Present climate pattern ENSO. Two climatic zones.
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Climate of Australia Ian Rutherfurd
Global Position • Topography
This lecture … • Context of Australia • Summary of climate • Aridity • Present climate pattern • 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
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
Flat Murray falls 100m from Albury 2200 km from sea Mean height = 300m World average = 700m
Consequences of aridity … • Landforms • Vegetation • Animals
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)
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
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
Arid • Position + Flat • Tropical/monsoonal • Temperate • Global Position • Topography