Adelaide

1972 - 1989

The population of the state of South Australia grew from 1 200 000 at the time of the 1971 census to 1 401 000 in 1991. This is a 17% increase in twenty years or an average of just less than 1% per year.

Where did this population grow? In the urban areas, in keeping with the national trend. If we take the Adelaide Statistical Division as the city of Adelaide, some 72% of the population of this state resided there in 1971, increasing to 73% in 1991. South Australia is an urbanised state, but the city of Adelaide itself is compact. It occupies an area of 664 square kilometres, or just 0.07% of the total area of the state. Into this area is crammed 73% of the population giving an average density of 1540 people per square kilometre in 1991.

Three Landsat images of Adelaide: December 29 1972, January 28 1989 and the 1972-1988 Difference.

Use your browser to open each image in a new window to compare them.

What changes in the landcover of Adelaide occurred during the last twenty years? The earliest useful image of Adelaide was acquired on December 20, 1972 and this is compared with a cloud-free image acquired January 28, 1989, seventeen years later.

The urban complex of Adelaide lies on the plains between the Mount Lofty Ranges, the 'Adelaide Hills', in the east and the sea on the west. The urban area of Adelaide, as we have defined it here, spreads along its longest axis. The area is wedge-shaped and is orientated in a north - south direction. The northern base of the wedge is Port Adelaide with its distinctive (bright red) area of mangroves around Torrens Island and Barker Inlet. The southern point of the wedge is the seaside town of Moana.

The 'square mile' design of the city centre, with its corona of radiating roads is distinctive and clearly visible in both satellite images, particularly the 1972 FCC image. The area of the ice-blue inner city, high density suburbs and CBD is quite small and compact. The area of this type of urban landcover is obviously smaller than that in a city of comparable size, such as Brisbane. The difference in the area that can be detected from space is probably results from a difference in vegetation, particularly amenity plantings, between the two cities rather than a real difference in infrastructure.

By examining the 1972 FCC image, it is not hard to read the history of Adelaide from its geography. From an initial landing and settlement on the coastline just west of the city centre, the landcover of Adelaide plains - a grassy eucalypt woodland (eM2G, AUSLIG 1990) - was slowly cleared and converted into cereal crops and pastures. The soils and climate of the Adelaide plains are suitable for Mediterranean agriculture, and the initial colony prospered. However, as the population grew, patterns of economic activity changed. This in turn transformed the landcover of the Adelaide Plains: wheat fields, pastures, orchards and vineyards have become houses and roads. The urban areas expanded to the south to the point of the wedge, as well as to the north and north-east. The spatial pattern of the penetration of urban areas into agricultural landscapes is clearly visible at the northern base of the wedge. For better or for worse, some of the most productive agricultural soils in South Australia are now permanently covered by houses and roads.

Very little of the original vegetation remains in the Mount Lofty Ranges. This landcover, as well as that on the plains, was subject to change with the coming of European Australians. As an open eucalypt forest at time of settlement, it most probably increased in tree density and declined in grass cover as the frequency of burning by Aboriginal Australians decreased. Then a pattern of landcover change followed as the land was used for increasingly intensive agricultural purposes; pastures, cropping and horticulture. With the continuing drive of Urbanisation, and the limited areas for expansion of the city on the plains, the near-agricultural areas of the Mount Lofty Ranges have been also transformed. Urban expansion of the existing small towns has occurred in company with the transformation of small holdings to hobby farms.

The landcover changes resulting from Urbanisation and other driving forces can be detected by examining the Difference FCC image and, if necessary, referring to the 1972 and 1989 images. I immediately point out one factor that will be a problem in our interpretation of landcover change. In the 1989 image there is a smoke plume lying over the Mt. Lofty Ranges. It appears to begin in the footslopes and streams southeast over the hills. Its presence in the 1989 image generates false change signals in the Difference FCC image.

The Difference FCC image flags surprisingly little change that we can attribute to urban expansion. The large black areas in the Northeast are clearly new suburbs. The shape and location of these areas of change indicate the conversion of agricultural to urban landcover. There are smaller more diffuse areas of change in the southern suburbs, the area of much of Adelaide's growth. The most extensive areas of dark tones show in the north of the image, where presumably crops in 1972 appear as bare ground or fallow in 1989. These changes are temporary and of no interest.

There are a multitude of very small areas of change scattered throughout the Mount Lofty Ranges next to the south-eastern Freeway that suggest that some of this change may not be small scale agriculture, but includes Urbanisation, the intensifying of rural towns and villages. If you explore the Ranges you can detect new roads, freeways and water storages. The spatial rather than the spectral pattern of this landscape has changed during the Looking Back period. It appears a little more 'busy'. This fragmentation and division of the landcover suggest an urban intensification that is not detectable using our spectral criteria.

In summary

Adelaide is a city that is bounded by natural constraints on two sides. Most of its growth over the last few decades has been along its longest (north - south) axis at the expense of productive agricultural landcover. The population of South Australia is growing relatively slowly but most of that growth is in Adelaide. During its modern growth, Adelaide became a Car City. Over the sixteen years we have looked back, very few extensive and coherent areas of urban expansion could be detected. Instead, there appear many small and diffuse landcover changes occurring because of the progressive Urbanisation of the previously agricultural areas of the Mt. Lofty Ranges. This Car City is overcoming its natural boundaries.