Variability in urban population distributions across Africa

Cascade Tuholske,Tom Evans,Ryan Avery,Kelly Caylor

doi:10.1088/1748-9326/ab2432

Cascade Tuholske, Tom Evans + Show 2 more

Open Access

https://doi.org/10.1088/1748-9326/ab2432

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Abstract

Africa is projected to add one billion urban residents by 2050. Yet developing sustainable solutions to tackle the host of challenges posed by rapid urban population growth is stymied by a lack municipality-level population data across the continent. To fill this gap, we intersect volunteered urban settlement data from OpenStreetMap with five synthetic gridded population datasets to estimate the how Africa’s urban population is distributed among over 4750 individual urban settlements across Africa. We assess how urban settlement distributions changed from 2000 to 2015 within and between countries and across moisture zones. To this end, we construct urban settlement Lorenz curves to calculate change in Gini coefficients and test the degree to which Africa’s urban settlements distributions fit power law distributions exhibited by Zipf’s law. Our results reveal that 77%–85% of urban settlements in Africa have fewer than 100 000 people and that at least 50% of Africa’s urban population live in urban settlements with fewer than 1 million residents. Across almost all African countries, the distribution of urban population shifted towards larger cities between 2000 and 2015. However, in arid regions, our results indicate that small- and medium-sized urban settlements are absorbing a greater share of urban population growth compared to large urban settlements. While our urban population estimates vary across gridded population datasets and differ from United Nations estimates, this is the first paper to measure urban population across Africa using a consistent methodology to identify urban settlement populations. Unlike UN urban population data for Africa, our results can readily be incorporated with geolocated environmental, public health, and economic data to support efforts to monitor United Nations Sustainable Development Goals related to urban sustainability, poverty reduction, and food security across Africa’s ever-growing urban settlements.

Highlights

Africa is projected to add one billion urban residents over the thirty years, ballooning from 491 million in 2015 to nearly 1.5 billion by 2050 [1]
Comparative estimates of Africa’s urban population by settlement size The total number of Africans estimated to be living in urban settlements ranges from 479.15 for WorldPop 2015 to 608.89 million for World Population Estimate (WPE) 2016
Total urban population grouped by settlement size varies considerably by gridded population data sets (figure 2(a)), though across all data sets urban settlements with 1–5 million people encompass the greatest share of urban population by settlement size category (figure 2(a)) While UN data shows that 65% of urban Africans lived in urban areas with fewer than 1 million people in 2015 [1], our estimates range from 42% for LandScan 2015 to 50% for GHS-Pop 2015

Summary

Introduction

Africa is projected to add one billion urban residents over the thirty years, ballooning from 491 million in 2015 to nearly 1.5 billion by 2050 [1] Such rapid urban growth presents a host of challenges for the continent’s development prospects. Troubling research from South Asia suggests that some African cities may become inhospitable as climate change produces more frequent extreme temperatures in mid-latitude regions [9]. Together these mounting challenges raise concerns for Africa’s ability to achieve United Nations Sustainable Development Goal 11 to ‘Make cities and human settlements inclusive, safe, resilient and sustainable’ [10]

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