The region's population is growing at a rate of about 1.2% yr-1, approximately equally from natural increase and immigration. The population is progressively aging, in line with other OECD countries. Health status is improving, but indigenous peoples lag significantly. The main population centers are growing faster than rural areas. Australian lower latitude coastal zones are developing two to three times faster than the Australian average (see Section 12.6.4), for urban/suburban uses and for recreation and tourism. In New Zealand, there is a steady internal migration northward to Auckland.
Agricultural commodity prices have tended to fall, but yields per hectare have risen, and farm sizes and total volume of production have increased (ABARE, 1997; Wilson and Johnson, 1997). Average return on agricultural assets is low. Service industries are an increasing fraction of all industry, and there is a trend toward more intensive agriculture and forestry and to diversification of rural land use, including specialty crops and tourism. There is increasing competition for water in areas of low rainfall where irrigation is essential to intensive cropping; urban demands are rising quickly, and water is needed to maintain natural ecosystems (Hassall and Associates, et al., 1998). Tourism is a major growth industry that is increasing the pressure on areas of attractions such as coastal zones and reefs.
Environmental concerns include air and water pollution from urban industries, land transport, and intensive farming and related processing and soil erosion, rising water tables, and salinization. Environmental management increasingly is based on the principle of sustainable management, as enshrined in New Zealand's Resource Management Act, and an integrated approach to environmental impacts in both countries. A major trend to a "user pays" principle and, especially in Australia, to market-driven water rights, with caps on irrigation supplies, is causing significant changes in rural industry. However, there still are many instances, particularly in coastal management, where these principles are not applied.
Trends identified in the region continue to be generally consistent with those elsewhere in the world. Research on regional trends has been summarized in Salinger et al. (1996) and in specific studies by Plummer (1996), Torok and Nicholls (1996), Holbrook and Bindoff (1997, 2000), Lavery et al. (1997), Plummer et al. (1997), Zheng et al. (1997), McKeon et al. (1998), Collins and Della-Marta (1999), Hennessy et al. (1999), and Plummer et al. (1999).
Mean temperatures have risen by 0.05-0.1ºC per decade over the past century, with a commensurate increase in the frequency of very warm days and a decrease in the frequency of frosts and very cold days (Plummer et al., 1999; Collins et al., 2000). Nighttime temperatures have risen faster than daytime temperatures; hence, the diurnal temperature range has decreased noticeably in most places. The past decade has seen the highest recorded mean annual temperatures.
Trends in rainfall are less clear. Australian annual mean rainfall has increased by a marginally significant amount over the past century (Collins and Della-Marta, 1999; Hennessy et al., 1999). However, increases in the frequency of heavy rainfalls and average rainfall are significant in many parts of Australia. Average rainfall has increased most in the northwest and southeast quadrants (Collins and Della-Marta, 1999). The largest and most statistically significant change has been a decline in rainfall in the winter-rainfall-dominated region of the far southwest of western Australia, where in the period 1910-1995, winter (June-July-August, JJA) rainfall declined by 25%, mainly during the 1960s and 1970s. Previous studies (Wright, 1974; Allan and Haylock, 1993; Yu and Neil, 1993), as well as a more recent one (Smith et al., 2000), have noted this decrease and attribute it to atmospheric circulation changes, predominantly resulting from natural variability.
There are marked interdecadal variations over northern and eastern Australia in summer half-year rainfall, which are dominated by ENSO-induced variations (Power et al., 1999a). There also are clear interannual and decadal variations in central and eastern Australian rainfall associated with Indian and Pacific Ocean sea surface temperatures (SSTs) (Power et al., 1999b). Some of the regional linear trends observed during the past century merely may reflect a particular pattern of decadal variation. Thus, the high degree of decadal variability may enhance or obscure a signal that is related to climatic change for several decades. A growing body of evidence is being obtained about past climate variability from coral cores (e.g., Lough and Barnes, 1997; Isdale et al., 1998; Quinn et al., 1998).
The strength of the relationship between eastern Australian climate and ENSO has been observed to vary over the past century. This seems to be linked to longer term climate oscillations such as the North Pacific Decadal Oscillation (NPDO) (e.g., Power et al., 1999a). Salinger and Mullan (1999) examined the 20-year periods before and after 1977 and showed increases after 1977 (some statistically significant) in mean rainfall for New Zealand's west coast, associated with strengthening westerly winds. These fluctuations in rainfall are partially explained by the increase in El Niño conditions over recent decades. There is some evidence of long-term variations in the Australasian region in storm frequency and tropical cyclones (Nicholls et al., 1996a; Radford et al., 1996; Hopkins and Holland, 1997; Leighton et al., 1997). Nicholls et al. (1998) show that although there has been a decrease in tropical cyclone numbers from 1969 to 1996 in the Australian region (105°E to 160°E), there has been an increase in the frequency of intense tropical cyclones with central pressures of less than 970 hPa.
The average rise in sea level in the Australia/New Zealand region over the past 50 years is about 20 mm per decade (Rintoul et al., 1996; Salinger et al., 1996), which is within the range of the current estimate of global sea-level rise (IPCC, 1996, WGI Section 7.2.1). However, the greater frequency and duration of El Niño episodes since the mid-1970s has reduced local New Zealand sea-level trends: The average sea-level change since 1975 at Auckland is close to zero (Bell et al., 1999). There has been a weak warming trend in ocean temperatures to 100-m depth in the southwest Pacific (39°S to 49°S, 141°E to 179°E) of about 0.13°C during the 34-year period 1955-1988 (Holbrook and Bindoff, 1997), and there have been shorter period SST fluctuations associated with ENSO.
Other reports in this collection