Combined Components of Population Change by Territorial Authority Area
These maps show the combined contribution to net population change from natural change (births minus deaths) and net migration (known as ‘components of change’), for each of New Zealand’s 67 territorial authority areas, for the observed period (1996-2013) and projected period 2013-2043 (see below for data sources and methodology).
The maps depict how the components of change interact to result in three types of growth and three of decline (drawing on Jackson, Cameron & Pool 2015, and Jackson, Brabyn & Maré 2016). The framework also recognises two types of zero growth, but for our purposes here we show only zero growth.
Type A growth (shown on the maps in bright red) occurs when both natural increase and net migration are positive. In Type B growth (orange shading), natural increase is positive and offsets accompanying net migration loss. In Type C growth (pink shading), natural increase is negative (i.e. there is natural decrease) but it is offset by net migration gain.
Type D net population decline (pale blue shading) occurs when there is net migration gain, but it is insufficient to offset accompanying natural decrease. The opposite occurs to result in Type E decline (mid-blue shading): natural increase is positive, but is insufficient to offset accompanying net migration loss. In Type F decline (dark blue), both natural increase and net migration are negative.
These maps show that while natural increase has played a major role in offsetting past net migration loss at territorial authority area level to deliver growth, natural decrease is slowly emerging, and will soon become much more widespread, leaving territorial authority areas experiencing net migration loss, increasingly ‘unprotected’ (Jackson and Brabyn 2017; Jackson and Cameron 2017).
Data Sources and methodology: Data for the period 1996-2013 were calculated using the three-step process described below; data for the projected period 2013-2043 were drawn directly from Statistics New Zealand (2015b) Subnational Population Characteristics, medium variant projections 2013(base)-2043 (note that these projections have since been superseded with the 2043 Update).
Step 1: First we obtained, from Statistics New Zealand (2016), births and deaths data (based on birth and death registrations) for territorial authority areas, for the years ending June 1997-2013, based on 2013 geographic boundaries. All data had been randomly rounded by Statistics New Zealand to base 3. We also sourced Estimated Resident Population by age and sex (Statistics New Zealand 2015b).
Step 2: From these data we calculated natural increase (births minus deaths). Natural Increase was then subtracted from net change in Estimated Resident Population, to generate a residual measure of net migration.
Step 3: The natural increase/decrease and net migration components were then compared with the direction of net population change (positive or negative).
Jackson NO and L Brabyn (2017) ‘The mechanisms of subnational population growth and decline in New Zealand, 1976-2013’ Policy Quarterly Supplement 13: 22-36. http://igps.victoria.ac.nz/publications/PQ/2017/PQ-Vol-13-Supplementary-2017.pdf.
Jackson, NO, L Brabyn and D Maré (2016) New Zealand’s towns and rural centres 1976-2013 – experimental components of growth’. Working Paper No. 7. National Institute of Demographics and Economic Analysis, University of Waikato, Hamilton New Zealand. http://www.waikato.ac.nz/__data/assets/pdf_file/0017/324134/No7-New-Zealands-towns-and-rural-centres-1976-2013.pdf
Jackson NO and MP Cameron (2017) ‘The unavoidable nature of population ageing and the ageing-driven end of growth - an update for New Zealand’ Population Ageing: 1-26. DOI: 10.1007/s12062-017-9180-8.
Jackson, NO, MP Cameron and I Pool (2015) The mechanisms of subnational depopulation – towards a typology. Session presentation to ‘Our People, Our Places’, Population Association of New Zealand Biennial Conference. Hamilton. June 29-30.
Statistics New Zealand (2016) Customised database. Estimated birth and death occurrence, at 30 June 1997-2013 by Territorial Authority Area of Usual Residence based on 2013 boundaries.
Statistics New Zealand (2015a) Subnational population by age and sex, June 1996, 2001, 2006, 2013.
Statistics New Zealand (2015b) Subnational population projections, characteristics, 2013(base) -2043 (medium variant).