Causes of population decline
The components of population growth are birth, deaths and international migration. For a population to grow, the number of births and immigrants (inflow) must exceed the number of deaths and emigrants (outflow). When the outflows exceed the inflows, the population will decline.
Current population projected to decline
New Zealand's population currently comprises just over 4 million people. Projections indicate that the population is unlikely to exceed 5 million without significant and historically unsustainable long-term gains in international migration and/or a return to high fertility. From about the middle of this century, the size of the population may begin to decline.
Recent patterns of population change
In recent history, permanent and long-term migration patterns for the New Zealand population have been very volatile, with periods of population gain due to migration and periods of net loss of migrants.
Over the last century, the average net gain from international migration has been around 5,000 people per year.
However, during the period from the early 1970s to the late 1990s, virtually all growth came from natural increase with very little gain due to international migration. With expected global competition for migrants, it is likely that this scenario will become the norm.
Projections based on small, steady international migration gain
The projections that the population will peak at around 5 million assumed that the long-term average gain of 5,000 people per year would be maintained.
Increased life expectancy
Even though fertility has declined, the population has continued to grow as life expectancy has increased. This has resulted in more people in the older age groups. The ageing population will present an increase in the number of deaths.
Changing fertility patterns
Changes in fertility patterns are resulting in relatively smaller childbearing age groups and women are expected to be having fewer children later in life. This changes the timing and the spacing of births - not only will there be fewer births per woman, but the number of women having children will fall and the generation length will increase.
Result: population decline
Thus, if there are fewer births and fewer immigrants at the same time as there are more deaths and relatively more emigrants, the population will decline. The challenge for policy makers is to either seek ways to modify this pattern or devise solutions to ameliorate the consequences.
Decline is temporary
The key point is that this scenario is temporary. Any population decline is likely to be relatively short-lived and will continue only while the older cohorts are large enough to contribute more deaths than the childbearing cohorts produce babies. The population will eventually stabilise into a new structure. How long the transition lasts and how severe the consequences will depend directly on the timing of this transition and the relationship between the various components of this change. What is clear, though, is that the period is measured in decades, it is predictable and it can be planned for.
How ageing is related to population decline
Potential population decline should be considered along with population ageing.
The ageing of the population experienced in the late 20th and early 21st century is a precursor to population decline. The relationship between ageing and population decline can be seen in the relationship between the population size and the changes in median age suggested by population projections.
Under the most plausible scenarios, population projections indicate that the peak in population size will occur around two decades before the peak median age. Ageing will continue for a time even after the onset of population decline. However, this will probably be followed by a slight drop in the median age before the population age structure settles into a new equilibrium.
Decline and regional development
Regional diversity in population change is of increasing importance, not just at the local level, but with social and economic implications nationally.
Some local authority territories are already experiencing significant losses of people in key economic age groups resulting in labour shortages and infrastructural stresses. These areas have rapidly ageing populations, large demands for seasonal workers, large outflows for education or health needs and similar special features.
Other areas are affected by inflows of people in some age groups at the same time as they experience outflows in different age groups. In an environment of general decline in population size, the consequences of these lop-sided flows may become significant for policy planning.
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