World’s Soil Resources

15.3 | Climate
The climate of the region is strongly influenced by circulation patterns and processes in the Pacific Ocean
(the Southern Oscillation) that bring La Niña conditions associated with floods and cyclones and El Niño
conditions that are associated with droughts. A similar circulation pattern in the Indian Ocean (the Indian
Ocean Dipole) influences drought across southern Australia. The Southern Annular Mode of the Southern
Ocean affects weather and climate in New Zealand and southern Australia. These large-scale circulation
processes interact with the landscape (e.g. through orographic processes and in accord with the scale of
the land mass) to exert a strong control on land use and management across the region. Some of the most
significant features are as follows.
• Australia has a very highyear-to-year rainfall variability, and major droughts and wet periods occur on
a decadal scale. Resilient systems of land and water resource management are essential to deal with
this level of climate variability.
• Landscapes in the tropics and sub-tropics experience cyclones and very high intensities of rainfall
especially in coastal areas. Maintenance of surface cover is essential to avoid extremely high rates of
soil erosion.
• The wet-dry tropics of northern Australia and some Pacific Islands receive most of their rainfall in three
consecutive months and the remainder of the year is severely water-limited. This restricts options for
land use unless some form of irrigation is possible. The harsh climate, in conjunction with the ancient
and strongly weathered soils, largely accounts for the dramatic difference in land use and population
density of Northern Australia when compared to nearby Indonesia and Papua New Guinea.
In some parts of the region, there is a sensitive interplay between rainfall, evaporation and the capacity
of soil to store water. Many soils in southern Australia have a limited capacity to store water and this makes
them especially vulnerable to small changes in the distribution and amount of rainfall. As a consequence,
relatively small changes in rainfall and temperature caused by climate change are having a significant impact
on farming systems and water resources (Reisinger et al., 2014). Likewise, sea-level rise caused by global
warming (Nurse et al., 2014) creates an immediate and serious threat to thousands of low lying atoll islands
in the region.
15.4 | Land use
15.4.1 | Historical context
The history of human settlement has occurred in several distinct waves over a very long period. In every
case the impact on soils has been substantial and in some cases catastrophic. The earliest records indicate
that human arrival occurred in Papua New Guinea and Australia at least 45 000 years BP. At this time, sea
levels were much lower and a land bridge connected the two countries forming the single continent of Sahul.
This continent was widely colonized by 35 000 years BP (O’Connell and Allen 2004).
It is difficult to assess the impact on soils caused by the initial colonization of the region, particularly by
the Australian Aborigines, because it coincides with a period of rapid climate change towards the end of the
Pleistocene. In Australia, major changes in fire, vegetation, and wildlife occurred (Roberts, Jones and Smith,
1990; Roberts et al., 1994; Bowler et al., 2003; Turney et al., 2001). The cumulative effect on soils caused
by humans and other environmental drivers during this time may rival the later direct impact caused by
Europeans, although the latter has been concentrated into a very short period.
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
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in the Southwest Pacific