Northern Australia

A billabong in the Kakadu National Park, Northern Territory. The monsoon climate of northern Australia is hot and humid in summer.

Almost all of Northern Australia is a huge ancient craton that has not experienced geological upheaval since the end of the Precambrian. The only exception to this generalisation is the Wet Tropics of northern Queensland, where active volcanoes have been present as recently as the Pleistocene.

The vast craton in the north and west contains a number of quite rugged mountain ranges, of which the highest are the MacDonnell and Musgrave Ranges on the southern border of the Northern Territory. These rise to over 1,500 metres (4,900 ft), but the most spectacular features are the deep gorges of rivers such as the Finke. Most of the craton, however, is distinctly flat and generally low-lying with an average elevation of around 400 metres (1,300 ft), whilst in the Lake Eyre Basin most of the land is not far above sea level.

The climate of the north of Australia ranges from arid (Köppen BWh) in the south to monsoonal (Köppen Aw) in the Top End and Kimberley. On the eastern coast, however, the climate is much more humid and ranges from humid sub-tropical (Köppen Cfa around Brisbane and Cwa further north) to humid tropical (Köppen Am and Af) in the Wet Tropics. Except in the western part of the Pilbara and Gascoyne where the heaviest rain often occurs from May to July under northwest cloudbands, rainfall is heavily concentrated in the "summer" months from November to March. For instance, in Burketown, the months May to September are rainless in over fifty percent of years, with over eighty percent of Augusts having no rain.[2]

Temperatures in summer are generally unpleasantly hot apart from the eastern coastal belt. Maximum temperatures elsewhere between October and April range from 30 °C (86 °F) in the south in April to around 40 °C (104 °F) in the inland Pilbara and Kimberley before the wet season breaks. Further north, maxima are consistently around 32 °C (90 °F) but extreme humidity makes conditions very unpleasant. On the coast, maxima in January range from 29 °C (84 °F) in the south to 32 °C (90 °F), with minima generally around 21 °C (70 °F).

In July, temperatures show a wider range, from 31 °C (88 °F) in the north to around 19 °C (66 °F) in the south, where minima can be as low as 5 °C (41 °F) in Alice Springs in June and July.

Except in the Lake Eyre Basin and adjacent areas to the east, the soils of Northern Australia are quite remarkable in global terms for their low fertility and difficulty of working. Most of them consist chiefly of hard laterite developed during period of climate much more humid than even that of Darwin today. Since there has been no mountain building in the region since the Precambrian and no glaciation since the Carboniferous, the region's soils have generally been under continuous weathering without renewal for over 250 million years, as against less than ten thousand for most soils in Europe, Asia, North America and New Zealand which have been formed from recent mountain building or glacial scouring of the land.

This immensely long weathering time means that nutrient levels in Northern Australian soils are exceptionally low because practically all soluble minerals have long been weathered out. The major constituents of most soils in Northern Australia are iron and aluminium oxides, both of which are not only very insoluble but also serve to reduce the soil pH and remove phosphorus from the soil as insoluble iron and aluminium phosphates. The insolubility of these metal oxides also serves, under the extremely harsh conditions during the dry season in the north and generally in the south, to create massive sheets which are impossible to plough.

In the Lake Eyre Basin, deposition from volcanic regions to the east has produce cracking clay soils of quite high fertility which are still often fairly low in phosphorus but have very good levels of potassium, calcium and sulfur. These soils provide the best grassland for grazing in the region. The youthful, volcanic Wet Tropics has a number of areas of fertile alluvial soils that support intensive horticulture.

The extreme soil poverty of most of Northern Australia has the effect of confining large herbivores such as the kangaroo to the better soil in the dry grasslands since they cannot digest the extreme poor fodder from the northern monsoonal regions. However, the frequency of fires during the desiccating dry season from May to September means that forests cannot establish themselves except in sheltered places. This has created a unique type of tropical savanna environment in which fires play a crucial role in elevating the extremely low nutrient levels and aiding growth during the wet season.

The many large rivers of the region such as the Mitchell, Gilbert-Einasleigh, South and East Alligator, Daly, Ord and Fitzroy support populations of the saltwater and freshwater crocodiles, which are by far the best-known animals of the region. There are also a number of species of python. Further south, where rivers are not adequate to support crocodiles, there exist a number of quite unique lizard species.

The Wet Tropics, like all tropical rainforests, is very rich in unique species, and importantly contains some of the most primitive flowering plants in the world.

Northern Australia faces major challenges to economic growth. Although the climate and soil poverty have defied all attempts to develop large-scale agriculture in large parts of Northern Australia, some agricultural and horticultural industries have seen strong growth. For example, in the Wet Tropics, mango, sugar cane and banana growing are major industries. Northern Australia produces more than 93% of Australia’s mangoes,[4] more than 94% of Australia’s bananas,[5] and more than 95% of Australia’s sugar.[6] Sheep and beef cattle are also raised successfully across Northern Australia, usually on extremely large properties. Northern Australia accounts for 64% of Australia’s national beef cattle herd.[7]

The geological factors that make Northern Australia's soils so unsuited to traditional agriculture, however, make it extremely rich in ores of abundant, insoluble lithophile metals such as aluminium, iron and uranium. It has the world's largest deposits of all these metals, and as less reactive chalcophile metals have been depleted Northern Australia has become very important to the economies of mineral-poor Asian nations. It was Northern Australian iron ore that fed the Japanese post-war economic miracle and the Four Tigers of South Korea, Taiwan, Hong Kong and Singapore. At 2015, Northern Australia accounted for over 70% of Australia’s known resources of iron ore, lead, and zinc.[8]

During the 1950s and 1960s, the government of Robert Menzies attempted to develop farming in Northern Australia, but pests made this impossible even when varieties of rice suited to the soils were developed. Today, however, sugar cane growing has expanded into the Ord River basin without surpassing cattle and tourism as the main industries of the region.

• Eastern states of Australia
• North West Australia
• Southern Australia

• Richards, Leslie P (2007), A guide to cruising Northern Australia : anchorages Darwin to Carnarvon (4th ed.), Adventure Yarns, ISBN 978-0-9751857-4-2