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EnviroNorth > Mitchell Grasslands > Landscapes and Climate

Climate

Tropical and sub-tropical climate

The Mitchell Grasslands is the only landlocked region of the tropical savannas. They stretch along the southern boundary of the Gulf region and have a similar elongated shape running in a north west-south east direction from the Northern Territory to central Queensland. Most of this area lies in a tropical climatic zone but southern sections extend into the sub-tropics where more arid conditions prevail in the characteristic wet summer and dry winter seasons.

Trade winds

This region's climate is controlled by the south-east trade winds which persist throughout the year except during the summer months when the north-west monsoons intrude into the northern sectors. In summer quasi-monsoons (modified trade winds) bring warm, moist, easterly to north-easterly winds to the south-east areas.

Rainfall

More than 80 per cent of rain falls between December and March - much of which is deposited by thunderstorms accompanying the monsoons or during the unstable, seasonal transition periods. They may occur on an average of 20 to 40 thunder days per year, which are most frequent in the north-west. The climatic effects of tropical cyclones rarely extend into this region.

Annual rainfall averages diminish from 600 mm in the north to less than 400 mm in the south making the Mitchell Grasslands the driest tropical savanna region. Variability of this rainfall is moderate to high with a high possibility of droughts occurring in the south. Run-off from heavy summer storms can cause dramatic changes in river levels over a short period of time.

Average temperature

The region's hottest temperatures occur pre-wet season but the slightly cooler, maximum January temperatures range between 36ºC and 39ºC when cloud cover and rain are most frequent. Climate discomfort occurs on 100 to 200 days each year with the more humid north being most strongly affected. January's relative humidity levels are around 30-60 per cent which begin to increase from about October after winter averages of 20-50 per cent.

Winter

During the longer winter season the south-east trade winds, which lose moisture as they cross the continent, blow consistently across the region so conditions are dry, skies are clear and temperatures are milder. July minimum temperatures range between 9ºC and 12ºC and frosts are a possibility in the far south-east sector on clear nights.