The world’s fastest growing cities
Which factors determine whether a city makes it onto the list of the world’s fastest growing cities? In the latest in a series focusing on the transition to a predominantly urban world, David Satterthwaite takes a closer look.
When I compiled a list of the world’s 20 fastest growing cities between 2000 to 2020 (see table 1), measured by population growth rates, I thought I had made a mistake. (I often manage to get the exponential growth rate formula wrong).
Looking at the list, I had never even heard of many of these cities. Where were the Kinshasas, the Delhis, the Dhakas and the Lagoses that have shot up the global rankings of the world’s largest cities?
A city’s population growth is usually measured by its annual average population growth rate. But city and national governments need to know the absolute change in population each year as this includes the number of newcomers (by birth or in migration) needing housing and public services.
Table 2 adds another apparent paradox. It lists the cities with the world’s largest annual increment in population from 2000 to 2020 – but many of these have relatively slow population growth rates.
A surprise: slow or no growth
We get so used to discussions on fast-growing cities that perhaps we forget to look at slow growing cities. Of the 1860 cities included in the United Nations database for 2000 to 2020, 107 had populations that were not growing or were indeed declining, and 311 had population growth rates between 0.1% and 1.0% a year.
The cities recording the largest absolute declines in population in these two decades were Detroit, Khulna and, tragically, Aleppo. (The data for Khulna is also a bit suspect; perhaps the statistics are for Khulna division, not Khulna urban agglomeration?)
Which cities are included in the analysis?
Any list of the fastest growing cities is going to be heavily influenced by which cities get included in the analysis. Table 1 draws from the UN Population Division’s database, which includes all cities that had 300,000 or more inhabitants in 2018.
By 2020, only one of the cities (Malappuram in India) had reached a million inhabitants. If the list of the fastest growing cities from 2000 to 2020 included cities with one million or more inhabitants in 2020, only Malappuram among the cities in table 1 would feature – the others (and all other cities with 300,000 to one million inhabitants) would be cut out of the analysis.
The world’s largest cities never appear in lists of the world’s most rapidly growing cities when their growth is measured by population growth rates – although they inevitably did when they were smaller.
The larger a city’s population at the beginning of any period for which population growth rates are being calculated, the larger the denominator used to divide the increment in the city’s population. Thus, it is not surprising that most of the cities in table 1 had relatively small populations in 2000. All had less than a million inhabitants; eight had less than 100,000.
When reviewing inter-census changes in population for all urban centres in a country, there are often small cities with very rapid population growth rates for one or two census periods – much more rapid than the cities in table 1. For instance, three cities in Kenya had annual average population growth rates of 13% or more between 1989 and 2009: Kiambu, Ngong and Ruiru.
This means that their populations increased more than tenfold in these two decades. But most do not sustain this very rapid growth; if they did they would become large cities. Or get absorbed into large cities that are expanding – all three fast growing cities mentioned above are close to Nairobi.
A very large city of 15 million is not going to grow tenfold in two decades. But some very large cities have doubled, or close to doubled, their population in the last two decades, including Delhi, Shanghai, Dhaka and Beijing.
Cities with the largest increment in population
However, if we consider the absolute number of people added to city populations each year, many of the largest cities figure prominently as the most rapidly growing cities.
The scale of their population increment is astonishing: Delhi getting an average of 730,000 new residents a year over these 20 years; Shanghai with 641,000; Dhaka with 536,000; Beijing with 509,000 per year; Sao Paulo with a slow population growth rate (1.4% a year over 20 years) yet still with a quarter of a million more persons a year.
Very large cities with more people moving out than moving in during 2000-2020 still had large annual average increments in their populations because of their very large size and rate of natural increase.
However, some caution is needed when comparing increments in population between cities, because boundary extensions or changing city or metropolitan government systems (which produce different boundaries) often include large populations that were not previously considered part of that city.
My blogs to date, including this one, have focused on cities (and mostly large cities). The next blog will look at the size of the world’s urban population, the scale of its growth and how its distribution between regions and between countries categorised by their per capita income has changed.
- Read Asia’s fastest growing cities… and why these are mostly small cities by David Satterthwaite (2023)