Global Urban Demographic Change is unfolding unevenly across cities worldwide, according to a new study published in Nature Cities. Researchers analyzed demographic data from more than 10,000 cities between 2000 and 2020 and found major differences in age structures, migration trends, and population growth patterns that national averages often fail to capture.
The study highlights how cities are becoming increasingly central to economic development, climate adaptation, and social stability. Yet, demographic shifts differ sharply depending on region, city size, and migration dynamics. While some urban areas are rapidly expanding through migration and natural population growth, others are aging or facing slower demographic change.
Researchers found that the global ratio of dependent populations — children and older adults — to working-age adults declined significantly during the two-decade period. The urban dependency ratio dropped from 0.87 in 2000 to 0.59 in 2020, reflecting the growing concentration of working-age populations in many cities. However, smaller cities consistently remained younger than larger urban centers, especially across Africa.
Smaller Cities Face Growing Demographic Pressures
The research revealed strong demographic contrasts between small and large cities. In African cities with populations below 50,000, dependency ratios remained especially high, indicating a larger share of children relative to working-age adults. Larger cities, by contrast, tended to attract working-age migrants seeking economic opportunities, lowering their dependency burdens.
Nigeria illustrated these differences clearly. Lagos, with a large working-age population, showed a much lower young dependency ratio compared with Kano, where children made up a substantially larger share of residents. Similar demographic divides were identified in Ethiopia, where smaller towns recorded some of the highest dependency ratios globally, while Addis Ababa showed much lower levels.
Researchers noted that these disparities could significantly affect economic productivity, public services, climate vulnerability, and long-term urban resilience. Smaller cities often receive less infrastructure investment despite housing rapidly growing populations, making them particularly vulnerable to economic and environmental pressures.
The study also examined urban sex ratios and identified major regional imbalances. Cities across the Middle East and North Africa displayed some of the world’s highest male-to-female ratios, largely driven by labor migration. In several Gulf-region cities, there were more than twice as many working-age men as women, reflecting sustained inflows of male migrant workers.
Meanwhile, cities such as Addis Ababa showed female-majority populations, demonstrating how migration and economic patterns can shape demographic structures differently even within the same region.
Migration Emerges as a Major Driver of Urban Growth
One of the study’s most significant findings involved the role of migration in urban population growth. Researchers estimated that global urban populations increased by 785 million people between 2000 and 2020. Of this growth, 45% was linked to net migration, while 55% resulted from natural population increase.
Regional differences were substantial. Cities in eastern and southern Asia recorded the largest population increases, with migration contributing nearly 70% of growth. In Sub-Saharan Africa, migration and natural increase contributed almost equally to urban expansion.
The study also found major variation between individual cities. In Burkina Faso, for example, Ouagadougou experienced rapid population growth largely driven by migration, while the smaller city of Koudougou expanded primarily through natural increase.
Researchers emphasized that migration is reshaping urban economies, labor markets, and demographic structures worldwide. Cities experiencing high levels of migration may see faster economic development but could also face greater social and environmental pressures, particularly in sectors vulnerable to climate risks.
The study concludes that city-level demographic data are essential for effective urban planning and sustainable development. By revealing how migration, fertility, and aging patterns differ between cities, the research offers a clearer understanding of the forces transforming urban populations globally.
