Dry Spells, Urban Swells: Analyzing the Drought-Induced Expansion of Cities in Sub-Saharan Africa

Rafael Van der Borght, Oscar Anil Ishizawa Escudero, Jean Thuret and Joaquin Ignacio Munoz Diaz

No 11099, Policy Research Working Paper Series from The World Bank

Abstract: Droughts are increasingly cited as a driver of urbanization across Sub-Saharan Africa, yet little is known about the role they play in shaping the spatial expansion of cities. Combining satellite imagery on built- up areas with climatic data for 1984–2015, this study empirically examines whether and to what extent droughts influence the spatial expansion of African cities. It further investigates the heterogeneity of these effects across cities and countries. The findings indicate that extreme droughts significantly accelerate the built-up growth rate of cities, while more frequent but less severe droughts have negligible impacts. Importantly, these effects are strongly differentiated across cities. The 1 percent most extreme droughts boost the average speed at which new settlements emerge in the surroundings of a country's largest city by 75 percent, yet they do not alter the expansion of smaller cities and towns. These drought-induced effects intensify the sprawl of the largest cities and bear important policy implications. Extreme droughts put additional pressure on the largest and often overcrowded cities, potentially deepening congestion effects. They also contribute to exacerbating the speed at which cities expand in flood-prone areas, thereby magnifying urban flood risk. As the climate changes, the frequency of both extreme droughts and extreme rainfall events is projected to increase across the region, aggravating the likelihood of future drought-induced expansions of the largest cities and worsening urban flood risk prospects. These findings call for urgent and tailored risk reduction measures in both cities and rural areas.

Date: 2025-04-10
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