Are migrants to blame for rapid population growth ?

Barely a day goes by without some comment in the media about the problems associated with high levels of immigration.  Overseas migrants are blamed for a range of problems, from traffic congestion to housing affordability and beyond.  There's no doubting that Australia's population is growing rapidly, but less attention is paid to how it is growing.  The ABS has recently changed the way they calculate population growth for sub-state geographies to a component based model.  This provides the opportunity to have a closer look at how the population is growing and changing at smaller areas of geography.

What are the components of population change?

People are born, they die, and they move around - this is how populations grow and decline, and are known as the components of population change.  The difference between the number of births and the number of deaths is called natural increase.  In Australia there are more births than deaths so the population will increase in the absence of any migration.  The reverse can also be true ie more deaths than births, and this is termed natural decrease.  In some parts of Australia this plays a significant role in population change.

Migration is the other component of population change, and can be considered in terms of interstate migration and overseas migration.  Interstate migration is between the states and territories and for Australia sums up to zero.  Overseas migration is between Australia and other countries - curiously in the debate over the level of overseas migration it's often forgotten that people do move out of Australia, so effectively media comments are about net overseas migration.

How is Australia's population growing?

In 2016-17 Australia's population grew by 388,120 persons - 124,710 through natural increase (37%) and 245,410 through net overseas migration (63%).  Overseas migrants overwhelmingly settle in NSW and Victoria (76%).  So yes it's true to say that net overseas migration is playing a major role in the rapidity of population growth, but clearly it isn't the only factor.

It is important to consider that migration is an extremely volatile component of population change.  Overseas migration in particular is subject to changes in government policy, and it's also reliant on economic conditions.  When jobs are plentiful levels of overseas migration increase simply because there are jobs available - you only have to consider the impact of the mining boom in Western Australia to see how this plays out demographically.  

On the other hand, natural increase is far more stable over time as changes in birth and death rates are influenced by societal change and health, which do not exhibit the same volatility over time.  Therefore, the contribution that each component makes to total population change is strongly influenced by the level of overseas migration.

How is Melbourne's population growing?

The new methodology employed by the ABS to calculate sub-state population growth provides an opportunity to see how the different components of change play out spatially.  Recently I looked at population growth in Victoria, observing that most growth was occurring in Melbourne.  Let's take that analysis a little further to look at the components of population change in Melbourne's LGAs.

Metropolitan Melbourne (defined by the 31 LGAs in the metropolitan area) grew by 123,360 persons in 2016-17.  Overseas migration comprised almost 65% of this total, natural increase 29% and interstate migration 7%.  Of all the growth attributable to overseas migration in Victoria in 2016-17, around 92% settled in Greater Melbourne.  

The map below shows the rate of population change through overseas migration for each LGA in metropolitan Melbourne.  Effectively this is what the growth rate would be if the only component of change was overseas migration.  All LGAs recorded population growth through overseas migration, but the spatial pattern was different to that of total population growth.

The City of Melbourne clearly stands out, with an overseas migration growth rate of 6.3% - by far the strongest in metropolitan Melbourne.  In numerical terms, this equated to 9,310 persons - around three-quarters of total population growth.  It is likely that this is related to the high number of international students residing in and around the city.  This is also likely to explain the higher overseas migration growth rate in Monash (3.5%).  2016 data from the Department of Education and Training indicates that over 33,000 international students were enrolled at the University of Melbourne and RMIT, both of whom have their main campus in the city.  A further 18,500 were enrolled at Monash University.  Of course international students are not the only overseas migrants but these enrolment statistics shed light on the scale of the contribution they make to population growth in our cities.

Interestingly, there was not a strong spatial relationship between the overseas migration rate and the rapidly growing LGAs on the urban fringe.  While overseas migration does play a role in population growth in these areas, they are more likely to grow through natural increase and interstate migration.  For instance, the City of Wyndham grew by 6.1% in 2016-17, but the overseas migration growth rate was 2.1%, the highest of the urban fringe LGAs.  This compares with 2.3% for interstate migration and 1.7% for natural increase.  

The lowest overseas migration rate (0.4%) was recorded in the outer urban LGAs of Mornington Peninsula and Yarra Ranges.  Both LGAs recorded modest growth overall, but natural increase (0.6%) was the more important in Yarra Ranges.  On the other hand, Mornington Peninsula recorded the lowest natural increase growth rate (0.05%) in metropolitan Melbourne, influenced no doubt by the older age profile in this LGA ie more deaths.

Summary

Overseas migration is the most volatile of the components of population change, responding to government policy and economic conditions.  The current high levels of population growth show some relationship with higher levels of overseas migration at the macro geographic level, but this doesn't translate well at the small scale.  Currently 65% of population growth in metropolitan Melbourne is attributable to overseas migration, but this varies widely by LGA.  The strongest overseas migration growth rate was recorded in the City of Melbourne, and the lowest in Yarra Ranges and Mornington Peninsula.