Adam Storeygard

Global trends in emerging infectious diseases.

Emerging infectious diseases (EIDs) are a significant burden on global economies and public health. Their emergence is thought to be driven largely by socio-economic, environmental and ecological factors, but no comparative study has explicitly analysed these linkages to understand global temporal and spatial patterns of EIDs. Here we analyse a database of 335 EID ‘events’ (origins of EIDs) between 1940 and 2004, and demonstrate non-random global patterns. EID events have risen significantly over time after controlling for reporting bias, with their peak incidence (in the 1980s) concomitant with the HIV pandemic. EID events are dominated by zoonoses (60.3% of EIDs): the majority of these (71.8%) originate in wildlife (for example, severe acute respiratory virus, Ebola virus), and are increasing significantly over time. We find that 54.3% of EID events are caused by bacteria or rickettsia, reflecting a large number of drug-resistant microbes in our database. Our results confirm that EID origins are significantly correlated with socio-economic, environmental and ecological factors, and provide a basis for identifying regions where new EIDs are most likely to originate (emerging disease ‘hotspots’). They also reveal a substantial risk of wildlife zoonotic and vector-borne EIDs originating at lower latitudes where reporting effort is low. We conclude that global resources to counter disease emergence are poorly allocated, with the majority of the scientific and surveillance effort focused on countries from where the next important EID is least likely to originate.

Farther on Down the Road: Transport Costs, Trade and Urban Growth in sub-Saharan Africa

This paper investigates the role of inter-city transport costs in determining the income of sub-Saharan African cities. In particular, focusing on fifteen countries whose largest city is a port, I find that an oil price increase of the magnitude experienced between 2002 and 2008 induces the income of cities near that port to increase by 7 percent relative to otherwise identical cities 500 kilometers farther away. Combined with external estimates, this implies an elasticity of city economic activity with respect to transport costs of -0.28 at 500 kilometers from the port. Moreover, the effect differs by the surface of roads between cities. Cities connected to the port by paved roads are chiefly affected by transport costs to the port, while cities connected to the port by unpaved roads are more affected by connections to secondary centers.

50 Years of Urbanization in Africa: Examining the Role of Climate Change

This paper documents a significant impact of climate variation on urbanization in Sub-Saharan Africa, primarily in more arid countries. By lowering farm incomes, reduced moisture availability encourages migration to nearby cities, while wetter conditions slow migration. The paper also provides evidence for rural-urban income links. In countries with a larger industrial base, reduced moisture shrinks the agricultural sector and raises total incomes in nearby cities. However, if local cities are entirely dependent on servicing agriculture so their fortunes move with those of agriculture, reduced moisture tends to reduce local urban incomes. Finally, the paper shows that climate induces employment changes within the rural sector itself. Drier conditions induce a shift out of farm activities, especially for women, into non-farm activities, and especially out of the workforce. Overall, these findings imply a strong link between climate and urbanization in Africa.

Is urbanization in Sub-Saharan Africa different ?

In the past dozen years, a literature has developed arguing that urbanization has unfolded differently in post-independence Sub-Saharan Africa than in the rest of the developing world, with implications for African economic growth overall. While African countries are more urbanized than other countries at comparable levels of income, it is well-recognized that total and sector gross domestic product data are of very low quality, especially in Africa. When instead viewed from the perspective of effective technology, as suggested in endogenous growth frameworks (and as proxied by educational attainment), the African urbanization experience overall matches global patterns. There are differences, however, at the sector level. Agricultural trade effects that improve farm prices deter African urbanization, while they promote urbanization elsewhere. Potential reasons include differences in land ownership institutions and the likelihood of agricultural surpluses being invested in urban production. Positive shocks to modern manufacturing spur urbanization in the rest of the developing world, but effects are dependent on the level of development. Thus many countries in Africa, with their lower level of development, do not respond to these shocks. Finally, historical indicators of the potential for good institutions promote urbanization both inside and outside Africa.