Australia : The Arid Country
Erasmus : My first impressions of Australia were gleaned from the words of a poem ‘My Country’. The core words describe ‘I love a sunburnt country’. They describe the tragedy of drought in the land. How the white ring barked forests face tragic towards the Moon. The pitiless blue sky, and how the farmers feel ill when they see their cattle die across the thirsty lands.
They describe the grey clouds gathering, rain like the drumming of an army, steady and soaking. And then over many days a veil of filming greenness thickens over the land, bringing her to life again. But ready to die once again, a brown and sunburnt land. (Dorothea Mackellar).
Australia is a predominantly arid country. Being arid implies that the region has prolonged dry periods. Generally in arid environments, the loss of water through evaporation from the land exceeds the rainfall.
Loss of water through evaporation from the soil makes it very difficult for plants to grow, as it exacerbates usual water losses. Even if enough rain falls and does not evaporate, it may soak into the ground or may flow away, leaving very little water available for local vegetation to utilise over the rest of the growing year.
Kinkajou : What are some other names for arid areas, especially any commonly used ones?
Erasmus : Lands which are arid are often described as dry forest, dry bush, brush land, grassland, or savannah or deserts. Overseas, the term chaparral may be used. “Arid” in technical terms is usually defined as a region with an annual rainfall less than 500 mm. Arid regions are unsuitable for traditional agriculture, which relies on regular local rainfall. This does not mean that arid regions cannot be utilised for agriculture. It does mean that careful planning is needed to exploit the land for human use for agriculture.
Kinkajou : What follows is a rainfall map of Australia. Note how extensive the arid regions are in central and west parts of the continent. A good two thirds of the Australian continent could be described as arid.
Erasmus : Australia comprises a land area of about 7.692 million square kilometres. Although this is just five per cent of the world's land mass (149.45 million square kilometres). Australia is the smallest of the world's continents. It is also the lowest, the flattest and (apart from Antarctica) the driest. Approximately 20 per cent of Australia's land mass is classified as desert.
As well as having a low average annual rainfall, rainfall across Australia is also variable. The rainfall pattern concentrates at the margins of the continent, with the highest rainfall in the tropics and some coastal areas. There is an extensively arid core within the continent, covering almost two thirds of the Australian Continental land mass, being approximately 4,500,000 km².
Erasmus : The Following picture shows extensive drought affected areas in central Queensland. It also reveals the climactic variability across the continent, with distinct climactic zones along the eastern seaboard within inland Queensland and on the western coast centred around Broome and in the western bottom corner of the country around Perth.
Kinkajou : I wouldn’t have thought many people would live in deserts or arid areas of our planet. Life would be very difficult in these places indeed.
Erasmus : Not true. Throughout the world up to 1 billion people live in arid regions of our planet, many in the deserts. This creates the problem throughout the world of people living in arid environments, needing to feed themselves. As in Australia or the rest of the world, the land area affected by aridity is considerable. Much of the land is economically and functionally unviable for human habitation.
In Australia, very few people live within the inner arid zone of this continent. High temperatures, low rainfall, lack of water, distances from city based services and difficult economic circumstances all contribute to a very low population residing within Australia’s interior. Also Australia’s short history of colonisation has resulted in the people congregating within cities along the seaboard.
The population has not had the opportunity or time to spread out over the land. Farming is a commercial, not a subsistence based, mode of life. Today farming employs very few people typically with only a few per cent of the average country’s total population directly involved in food production.
Kinkajou : Australia’s deserts are certainly impressive. Though on a world stage very few people have ever heard of them.
Erasmus : Australia also has large deserts. There are deserts in Australia larger than many of the world’s countries. They cover huge expanses of ground. Yet, not even most Australians would know the names of these deserts. Do the names: the Tanami desert, the Great Sandy Desert or the Great Victoria Desert sound familiar? (Together they cover about 893 000 km2).
A desert is a generally defined as an area where the annual rainfall is less than 250 mm. The definition of deserts does not include Polar Regions. For instance, Antarctica with a rainfall of less than 10 mm per annum, is the world’s greatest desert, if you use the annual rainfall definition.
Deserts are found in the world:
- In Africa: the Sahara Desert, Kalahari Desert, the Sahel, and East Africa
- In Asia: the Indian or Thar Desert, the Namub desert, the Gobi desert, the Karakum desert, the Middle East
- Australia: the Great Victoria Desert, Great Sandy Desert, the Tanami desert and others.
- South America: the Atacama Desert, the Serrano of Brazil
- North America: much of the western USA, the Sonara desert
- Central America: the Pacific Coast
Kinkajou : But surely you can learn to deal with only having a limited rainfall every year.
Australian 10 Yr Cropping Outlook
Erasmus : Lack of rainfall is not the only problem in arid desert regions. Variability of rainfall is also a serious consideration. Most human economic models rely on recurrent annual cycles of human economic activity to generate sustainable income for people living in these regions.
In short, if you’re growing food in arid environment, having almost no annual rainfall for several years out of every 10 years, makes it almost impossible to undertake long term agricultural activities in these areas.
Kinkajou : Yes the following maps certainly do emphasise how variable precipitation can be. What is interesting is that precipitation is most variable in the driest regions of the Australian continent.
Kinkajou : The world needs more space for more people but an arid country like Australia would have trouble sustaining more population. So the arid regions of the Australian continent are considerable, but human habitation is often unviable. The ability to use the arid Australian landscape to grow food, or engage in other economic human activities, would be of considerable benefit to us all.
Kinkajou : Aren’t there specific species of plants which are very drought or arid tolerant?
Erasmus : As aridity increases there are fewer and fewer species adapted to living in arid environment and the potential biomass of species able to be supported across a landscape is also reduced. Aridity limits choices for agricultural exploitation. Some plants that cope well with aridity include:
- cereal grains such as pool millet,
- grain legumes such as Lablab bean, Tepary bean ,Mat been or Marama bean
- leafy vegetables such as Leucana
- root crops such as cassava
- fruit trees such as cashew or prickly pear or date trees
- feed legumes such as apple ring acacia, umbrella Vaughan, Jerusalem Thorn
- fibre plants such as sisal
- windbreak plants such as tamarisk species
- living fence plants such as Babul acacia
Millet Crop - Arid Country
Erasmus : I’ll mention the animals which are fairly aridity tolerant as well.
Different species of animals also vary in their adaptation to dry environments there has been considerable growth in the domestication and husbandry of goats within Australia. Goats have gone from being a pest animal to becoming a lean green source of protein. Currently it is thought that there are over 2 million goats living within the Australian outback.
They are very tolerant of varying types of feed. If one type of feed has disappeared or dried up, they’re very happy to eat many different types of feed, or scraps, or native species, or new fresh grass. This flexibility makes them often regarded as a garbage disposal system for the plant world.
Their flexibility unfortunately can cause land degradation, so it is crucial to manage grazing pressure exerted by goat herds on arid landscapes. Unlike sheep they require substantially less care in that they do not need to be sheared or crutched or drenched. (Crutching is the removal of genital / urinary region hair or wool).
Kinkajou : Are there any religions which have prohibitions about eating goats? I know that Hindus regard the cow as sacred. Jews regard Pigs as unholy (contaminated).
Dryland Farming Goats
Erasmus :As a meat it is widely accepted, there being no religious barriers to its utilisation. In some regions the wild goat population has endured and survived crippling droughts that have forced rangeland pastoralists in the same region to sell off all the sheep and cattle.
A major problem in dry land animal farming is the choice of feed for animals in the dry season. Options include harvesting and storage of wet feed as silage, dry feed as hay, grains as seeds , crop residues as dry season feeds, reducing the size of the herd at the onset of the dry season, or the final option of moving the herds to more productive or high rainfall areas. Common dry land animals include goats, sheep, donkeys and camels.
Kinkajou : Changing the climate could make a huge difference to the capacity of a country like Australia to support human population. But what changes are necessary? Very few people have looked at potential solutions to this problem. While there are many ways of engaging in arid farming practices, long-term sustainable solutions to exploitation of these regions demand that humans develop the capacity to control weather and to influence rainfall.
The Hobbit Shire. Australia is a very different country & humanity has grown past the stage of living this idyllic lifestylre. There are just too many of us.
History of Colonising the Arid Lands of Australia
Kinkajou : The arid environment has been an issue in Australia for a long time. It has affected the colonisation of the Australian continent. What can you tell us about the Australian experience?
Goyders Line for Sustainable Agriculture
Erasmus :In 1865 in Australia, a man named George Goyder proposed a demarcation line on maps which we have subsequently called the Goyder line. This demarcation line on the map generally represents a long-term rainfall average of approximately 250 mm. Goyder used a number of other factors in determining the location of this demarcation line.
The vegetation pattern was also used as generally the line demarcates the border between Malley scrub and salt bush vegetation.
What is the importance of the Goyder line? In in 1865, farmers needed reliable information to help them judge where sustainable agriculture farming could be undertaken. In the year 1865, there was prolific rainfall in South Australia. Many farmers headed further north, building farms and planting crops. However within a few years many had abandoned their farms.
Drought had arrived. Agriculture including many animal husbandry activities became unsustainable.
Goyder Line Cultivation Map
Erasmus : So the Goyder line demarcates the border between land where traditional agriculture relying on regular annual rainfall could exist versus land where the variability of rainfall and low rainfall would not allow sustainable traditional agriculture.
The Goyder line is still recognised today. It is regarded as an incredible feat of surveying, since Goyder who was the Surveyor General of South Australia, completed the entire surveying task within two months, accurately enough to still be relevant and useful today. This was in a colony founded in 1836, largely uninhabited apart from aboriginals, with very few rainfall records, those rainfall records in existence spanning a period of less than 30 years and only covering the areas where European settlers had colonised.
Today there are other definitions of this demarcation line.
The P/E ratio = Precipitation/Evaporation ratio is a contender.
Some authors have proposed that the ratio between rainfall during the growing season and potential evaporation gives a better approximation to the edge of the Australian grain belt in South Australia.
However although this ratio is useful in South Australia, it requires adjustment in other parts of the country due to climate and temperature varying the different regions. (The Tropical North, the temperate mid part of the continent, and the sometimes cooler regions of the South of the continent. Different predominant temperatures give different evaporative rates necessitating the adjustment of the P/E ratio.)
A P/E ratio of 0.26 (Precipitation/Evaporation) currently provides a better fit for the South Australian grain belt’s and current land utilisation. By using this ratio the speed of change in kilometres per decade can be assessed at the margins of the grain growing areas. This is critical in allowing farmers and governments to plan for climate change.
The definition is quite useful today and can be exported to other parts of continent. It implies there are many parts of the country where sustainable agriculture cannot be undertaken. These parts of the country also suffer from variability of rain creating regular droughts.
Rainfall is often very low. Temperatures within the continent and the more northern parts of the country are often quite high, resulting in substantial evaporative loss of water from the landscape. (In these regions, altered temperatures create changes in moisture evaporation, in effect extending the grain growing belt in the cooler regions.)
Goyders Line Sign Map
Kinkajou : I see the following maps give us some idea of the ambient temperatures across the Australian continent.
Just note the following example:
July is a winter month in Australia ,yet there are large parts of the Continental mass with temperature substantially above 27°, essentially year-round.
Kinkajou : The following chart shows some of the variability of Australian temperatures with the advent of climate change. The most notable observation is that Australia is getting hotter and probably drier.
Maximum Australian Annual Temperature
Maximum Temperature Winter Australia
Shifting Water: Irrigation in Arid Agriculture
Kinkajou : So we want to shift water from coastal areas into the interior of the continent?
Erasmus : To add 250 mm of rainfall across an area of 10,000 km² (i.e. an area of 100 x 100 km), would take a volume of water of 2.5 km³ (i.e. approximately 2 ½ thousand Giga litres i.e. again 2 ½ million mega litres or 2.5E12 litres.) (Water is very heavy and difficult transport. This equates to a weight of 2.5E12 kilograms or 2 ½ thousand million metric tonnes).
The metric ton, equal to 1000 kilograms, or approximately 2204 pounds. The metric ton is officially called tonne. The SI standard calls it tonne, (The U.S. Government recommends calling it metric ton.)
(There are two other sorts of tonne. The British ton is also known as the long ton equals 2240 pounds (lbs.). The US ton which is the short ton equals 2000 pounds.)
An area of 10,000 km² is a drop within Australia’s vast interior.
So the only practical method of moving this much water to the arid interior is to use the atmospheric envelope itself as a” weather engine “to move the water into the interior. The hydrological cycle of the planet itself, would do the work. It becomes obvious in this scenario that affecting substantial rainfall change throughout the interior involves vast quantities of water.
Again doing the maths, to add 250 mm of rain called across an area of 1000 km x 1000 km would involve a volume water of 250 km³.
And this is still a small area within the interior of the strain continent. And even with this extra rainfall, much of this 1000 km x 1000 km area would still remain borderline Arid. However arid with 500 mm of annual rainfall is a much more sustainable or economically usable situation than a desert with rainfall of less than 250 mm per annum.
Frankly, even climate or weather engineering to reduce rainfall variability is a valuable achievement for Arid Agriculture in Australia.
Kinkajou : The word “arid” covers a number of different sorts of climates doesn’t it?
Erasmus : Exactly, and this impacts on farming practices! To understand some of the existing dryland farming techniques I believe you need to understand a bit more about the concept of aridity. There are different sorts of aridity.
- For example, consider the case where a region has a dry climate but has seasonal rain. This type of aridity is more common in the tropical areas of the world, where monsoon seasons occur. The problem here is then to either conserve the water in the soil for the growing season or to grow plants and animals quickly in the growing season.
- Another example, is a situation where there was year-round aridity punctuated by light or regular rains. The problem here is to minimise the impact of the rain variability as well as to exploit what rainfall does arrive.
- A final example is where the effect of an arid climate is subverted through the use of irrigation, water being sourced from either bores (wells in other parts of the world) or canals. Problems here are directed at minimising water losses, but traditional rainfall type agriculture may be possible. Australia has insufficient free surface water to even remotely consider such a prospect.
Kinkajou : It is becoming obvious to me that those different techniques must be used in different situations of aridity.
Erasmus : Yes. However the principles of agriculture in arid climate remain the same.
Dryland farming techniques are based on a number of seemingly simple farming principles.
- Increase water absorption by:
- prevention of the development of a crust at the soil surface, often called a “sole” through tillage or ploughing practices
- stubble mulching, or dirt Mulching
- reducing water run-off using bunds or Contour strips, contour ploughing, or levelling of croplands
- Reducing the loss of soil moisture by:
- Planting shelter strips of trees or shrubs to reduce wind speed or to cast shadows. Generally, lands next to shelter strips are sheltered for an area approximately 2 ½ times the height of the trees in the sheltering strip.
- Mulching to reduce soil temperature and surface wind driven evaporation
- Shallow tilling to create dirt mulch. This will need to be replenished or redone after any rainfall to maintain the separation of the surface mulch layer from the deeper layers of the soil being used as water storage.
- Weed control
- Reduce plant transpiration water losses by:
- appropriate plant selection,
- for example dwarf varieties,
- plants with thin leaves,
- plants able to close their leaf stomas when hot to reduce water loss,
- plants with adaptations such as corn which can curl their leaves during the hot afternoon and open them at night, effectively reducing their leaf surface area to reduce transpiration,
- Plants utilising the C4 cycle such as succulents. (These plants store their photosynthetic by-products as intermediate 4 carbon acceptor compounds during the day, and undertake further processing or biosynthetic cycles at night.) The presence of C4 acceptor compounds within the plant locks in water stores by osmotic pressure.
Desert Crops of the Future
Other considerations include
- plants with deep or extensive root systems,
- plants which store water in the tissues and release water slowly,
- plants protected from water loss by wax on their leaf services,
- Plants with high desiccation tolerance.
Trees can often be the most useful crops in arid areas due to their deep roots making maximum use of groundwater and their potential to fulfil many purposes i.e. cropping soil conservation salinity control shade or windbreaks.
Shading, e.g. greenhouses. (Trees are often not used in arid environments for shelter strips or shading. Generally trees have extensive and deep root systems which remove water, usually exacerbating both moisture and fertility issues).
Erasmus : It is important to remember that when one is talking about the drought tolerance of plants one is generally talking about the drought tolerance of the growing or the mature plant. In most crops, seeds must be germinated under conditions of normal water availability.
Crop adaptation to arid regions is a very specialised science. Systems used by natives in many regions the world, although they appear archaic, would usually represent accumulated experience of centuries of experimentation. So often it can be very difficult to improve or change species that tolerate cultivation in many arid areas of the world.
The difficulties of the Australian climate and the lack of suitable plants or animals have essentially precluded Australian aborigines from developing farming. The Australian aborigines have remained nomadic hunter gatherers, perhaps utilising sporadic techniques for farming such as random distribution of seeds while eating or moving across the landscape.