Rural water availability and the growth of cities

joined work with Alexander Marbler, University of Graz, Wegener Center for Climate and Global Change, AUSTRIA

In this paper, we examine how climate-driven agricultural productivity shocks in rural areas affect economic activity in nearby cities and towns in Sub-Saharan Africa.

Little is known about how climate-driven rural out-migration affects nearby cities and towns. Existing studies analysing climate-driven rural-to-urban migration focus on urbanization rates and migration at the country-level or rely on infrequently collected survey data on individual migration decisions and infrequently available census data on population at subnational level within a single country or groups of countries. Instead, in this paper, we focus on the perspective of cities and seek to uncover how agriculturally relevant climatic shocks occurring in rural areas affect nearby cities and towns in Sub-Saharan Africa.

To answer these research questions, we assemble a rich set of high-resolution geospatial information to identify the size and location of cities as well as location-specific migration costs and agriculturally-relevant climatic shocks for rural areas in Sub-Saharan Africa.

We find the effect of climate-driven agricultural productivity shocks on city growth to be non-linear. Cities grow faster when there is less water available than normal during the growing season in the rurality of a city. Cities grow slightly slower when there are mildly wet conditions, which are favourable for agricultural production. This non-linear relationship is robust and observable over our entire sample of cities in Sub-Sahara Africa. Additionally, we show that these effects are heterogeneous, conditional on the initial size of cities.

Currently, around 55 percent of the human population lives in urban areas and by 2050 the global urban population is expected to increase by another 2.5 billion people. The UN projects that 90 percent of this increase is going to happen in Asia and Africa alone. The imminent urban growth due to climate change in Sub-Saharan Africa will also mean substantial changes for the African urban system. New cities will emerge, and existing cities are expected to grow substantially.