Darwin

1976 - 1988

To look back on the changes that have occurred around the city of Darwin, we have to choose our times carefully.

Darwin is the northern-most city in Australia. It is the undisputed focus of the wet-dry tropics, the top of 'The Top End'. In summer when the sun is high in the sky at Landsat overpass time (~0930 hours), Darwin is already covered by clouds that steadily increase in coverage during the day, and provide the spectacular late afternoon storms of 'The Wet'. To find cloud-free Landsat MSS scenes of Darwin, we had to settle for 'The Dry', the winter months. We will look back at the changes in Darwin that are visible from space over the period of just 12 years, from May 16, 1976 to June 1, 1988.

.Three Landsat FCC images of Darwin: May 16, 1976; June 1, 1988; and the 1976-1988 Difference.

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

My Territorian friends always impress upon me two important dates that must be remembered. I pass them on to you. The most recent is July 1, 1978 when the Northern Territory achieved self-government. The second date is January 1, 1974 when Cyclone Tracy largely destroyed the entire city in a few hours.

The devastation of Darwin in 1974 was not captured by space images, but its rebuilding and subsequent growth has been. The images are especially interesting because they capture not only the fascinating beauty of the Top End but also the dynamics of that society. The Territory is different from any other part of Australia, but the changes we will find are familiar.

The modern city of Darwin lies at the end of the Shoal Bay Peninsula and fronts the Timor Sea. It is a definitive terminus of the north - south Stuart Highway. The original settlement was surveyed by the Surveyor General of South Australia, Goyder, in 1869. He laid out a grid pattern, very similar to the city of Adelaide, for the city to be on a peninsula plateau. Initially called Palmerston, this settlement was renamed Darwin in 1911, but the imprint of the surveyor Goyder is still apparent in the pattern of Darwin today.

Between the census dates of 1971 and 1989, the population of Darwin has increased by a whopping 47%; from 39,000 in 1971 to 73,000 in 1989. This high growth rate of 2.6% per annum is slowing. The first count figures for the 1991 census show Darwin's population to be now 78,000 people; an increase of 6,000 since the 1986 census and an annual growth rate over these last five years of 1.6%. The lower growth rate may partly result from the development of the statistically separate satellite city of Palmerston. These changes that we detect in our satellite images are included in the Darwin urban area.

The Northern Territory has a low absolute population, 175,000 in 1991, but a high relative growth rate of 2.6%. Unlike the other states, Darwin is not the sole focus of this population growth. Only 47% of total population of the Northern Territory lives in Darwin. As a city-state, it ranks seventh; the second lowest, just ahead of Hobart.

The 1976 image of Darwin is striking in the tremendous spectral variation in the scene: the turbidity patterns in Port Darwin and Fannie Bay, the city itself on a small south-west pointing peninsula, the crimson red colours of the mangroves along the interface between land and ocean or of wetland vegetation lining the inland drainage patterns. The imposed pattern of human activity is readily detected. There are the geometric patterns of the Stuart and Arnhem Highways and tenure boundaries: sharp, straight lines in an otherwise intricately curved landscape.

There are also the naturally patterned darker areas. These are fire 'footprints', acres of charred vegetation and soot covered ground. Fire is an ever present feature of 'Top End' landscapes and we can see them here close to the city in 1976 and in 1988. At this later date the footprints are fewer and older. Their dark colour is more subdued as the soot and charred plant material have been dispersed.

The Difference FCC image captures the consequences of both influences on landcover; urban expansion with its permanent conversion of landcover, and fire with a temporary transformation of the vegetation. The change in cover because of urban expansion is obviously a much, much smaller area than that occupied by the fire footprints. The development of the satellite city of Palmerston and the suburbs in and around the urban centre of Casuarina are the two most prominent areas. Areas of urban infill, much smaller, can also be interpreted.

These landcover changes are insignificant in area when compared with that resulting from fire. Particularly striking in the Difference image are the white areas that indicate the very dark 1976 fire footprints that were not burned in 1988. The fire induced changes are temporary, it is thought, so while they dominate the landcover change in the Darwin area, they are of little significance compared with the urban expansion.

There is one (dark) area of vegetation cover loss that is intriguing. A large area of floodplain wetlands at the headwaters of Hope Inlet near Koolpinyah has changed. This area has become much barer and has less plant cover in 1988 than in 1976. The best interpretation I can make is that this area has been heavily grazed (by buffalo?).

Even though Darwin is the smallest city and the dominant changes we have found in looking back are due to natural rather than human forces, our perception can be further enhanced with higher quality satellite images. As for Canberra I include a high resolution SPOT image of Darwin as a glimpse of the future. This satellite is building an archive of images of Australia that began in 1986. When this book is rewritten in the year 2000, it will be done using images from the SPOT satellite to reveal the fine detail of landcover change.

In summary: In Darwin, the smallest but most dynamic of the capital cities, we have found the landcover change due to Urbanisation is small, but similar in nature and origin to that found in all the other cities. The very dynamic environment of the Top End provides a background that shows these changes to be small and insignificant.

What does it all mean? What is the take home message?