Sustainable Tropics - Frequently Asked Questions

• Where are the Australian tropics? 
• What are the tropics?
• How does the Southern Oscillation affect tropical climates?
• Why do cyclones occur only in the tropics?
• Why are the tropics important?
• What are the main environmental issues in the tropics?
• How are industries and government tackling these issues?
• What does CSIRO Land and Water do in the tropics?
• Where can I get more information on related issues?

Where are the Australian tropics?

Australia’s tropics begin at the Tropic of Capricorn and stretch across northern Australia from Rockhampton to Exmouth. Covering 42% of the country’s landmass, the tropical landscape ranges from arid, red desert at the country’s heart to rich rainforests along rivers and bordering the coast.

What are the tropics?

Covering a vast expanse of country, tropical conditions in Australia vary depending on latitude, topography and proximity to the coast. Broadly speaking, the tropical climate zone is characterised by two distinct seasons, ‘the wet’ and ‘the dry’. The dry season is stable with cooler temperatures, low humidity and clear skies. For much of the region, more water evaporates than falls as rain during the dry season.

The tropical wet brings extreme rainfall in heavy bursts from thunderstorms, widespread monsoon depressions or cyclones. These heavy rain surges generate 65% of Australia’s total water runoff with most of the water draining into the sea. Because of the seasonality and unreliability of the rainfall, people living in the tropics depend on dams and bores tapping into artesian groundwater for their water supply.

How does the Southern Oscillation affect tropical climates?

The extent and depth of the tropical wet and dry climate regimes are dominated by two phases of El Nino Southern Oscillation (ENSO). During the El Nino (dry) stage, a current of warm water near Peru causes surface winds to move rain clouds away from Australia. If this persists, drought conditions may result.

The system reverses during the anti-ENSO or La Nina stage, when warm waters near Australia cause surface air to converge. This results in heavy wet seasons for Queensland with the low-pressure phase making cyclones more likely. People living in the tropics may experience these overriding changes from El Nino to the anti-ENSO half a dozen times during their lifetimes.

Why do cyclones only occur in the tropics?

Cyclones are the most destructive natural threats to coastal communities. Tropical lows deepen into tropical cyclones from November to April, when ideal summer conditions mean warm, humid weather with sea temperatures above 26 – 27º C. The clockwise circulations of the atmosphere feed on warm moist air from the ocean surface, reaching heights of 10 – 12 kilometres into the troposphere. As the air rises it cools, water vapour is condensed and energy, once used to evaporate water, is released, increasing the system's activity. As pressure continues to drop, winds accelerate, heavy rains fall and the storm takes on the typical cyclone structure: a central ‘eye’ region of low pressure calm, surrounded by a swirl of destructive winds.

When the cyclone crosses the coast and continues moving inland, the inflow of moisture is reduced and the intensity declines within a few hours. The high winds do not usually extend further than 50 kilometres inland.

Why are the tropics important?

Tropical regions throughout the world are characterised by high levels of biodiversity. Much of Australia’s tropical areas are sparsely populated by people, so the ecosystem remains relatively untouched and the biodiversity is largely protected. The uniqueness of the region has not been lost on the international community and a number of World Heritage Sites are listed within Australia’s tropics, including the Wet Tropics rainforests, RAMSAR listed wetlands and the Great Barrier Reef Lagoon.

A growing tourism industry has developed because travellers are attracted to this rich, diverse and relatively untouched tropical region. Bioprospecting and research into ecosystem goods and services are also areas of economic growth based on the region’s great biodiversity.

Like most of Australia, tropical soils are often ancient, highly weathered and leached of nutrients, making crop and livestock production a challenge for most tropical farmers. Nevertheless, tropical agriculture is valued at over $3.5 billion in Queensland alone (State of the Environment, Queensland 1999). Grazing and cropping are the major agricultural activities with sugarcane as the main cash crop followed by grain sorghum, wheat, barley, cotton, peanuts, sunflowers, vegetables, bananas, mangoes, mandarins, pineapples and tobacco.

Cattle and sheep farming encompass an area about sixty times greater than the region dedicated to cropping and contribute $5.6 billion to the Queensland economy alone. Some of the world’s largest cattle stations found in tropical Australia.

Mining in the tropics generates a $13.5 billion income. Tropical Australia holds some of the world’s largest mineral ore bodies as well as a wealth of metal resources include copper, bauxite, lead, zinc, silver, nickel, tin, gold, manganese, uranium and magnesite. Diamonds, mineral sands, phosphate rock, kaolin, limestone and silica deposits are also mined in the tropics.

What are the main environmental issues in the tropics?

Degradation of the soil resource through salinity, erosion, long term monoculture, exposure of acid sulphate soils and loss of biodiversity is a serious threat to tropical production systems, while the export of sediments, salts, nutrients and contaminants to ground waters, waterways, wetlands and the Great Barrier Reef Lagoon are just a few of the environmental issues facing tropical Australia. For the past 200 years the Australian countryside has been exposed to intensive agricultural practices better suited to temperate regions, and some regions of the Australian tropics are no exception. The far-reaching consequences of inappropriate land use is damaging Australian industry as well as affecting environmental systems in the tropics and elsewhere in the country.

How are industries and government tackling these issues?

Because these issues can profoundly impact the long term sustainability of tropical Australia, almost all industry and public sector agencies are heavily involved in cooperative endeavours to address environmental degradation in the tropics. Committed to work with community and industry partners, CSIRO is a leader in collaborative endeavours to develop strategies for sustainable growth.

What does CSIRO Land and Water do in the tropics?

Operating through its Townsville-based Davies laboratory and the CSIRO laboratory in Atherton, CSIRO Land and Water provides leading-edge scientific research to develop solutions for sustainability in tropical agriculture, to assist in the preservation of the delicate ecosystems of the tropical north, and to support Australia’s important tropical industries.

On those sites and across Northern Australia, CSIRO Land and Water works in close collaboration with CSIRO Sustainable Ecosystems. We also maintain strong partnerships with government and industry, other research organisations including Cooperative Research Centres, universities, international aid and funding agencies and community organisations. Our scientists also work closely with our neighbours in the tropics to develop sustainable agricultural practices for the future, with the current focus in Thailand, China, the South Pacific Islands and Papua New Guinea.

Where can I get more information on related issues?

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• Educational material for students and teachers 
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