Research

Ongoing Work

Droughts and the growth of cities.  

Abstract: Some researchers and policymakers posit that climate change should increase city growth and urbanization as rising temperatures make rural livelihoods pre- carious, while others posit that climate change might trap rural households who cannot afford to migrate because of increasing poverty. Existing empirical evidence on the link between climate and urbanization is inconclusive. This paper provides new evidence, exploiting novel data that maps city growth for 7,000 cities in 108 low and lower-middle income countries across 23 years to provide new evidence on the relationship between drought and urbanization. Cities experience large and persistent declines in growth rates after major drought events: after 11 years, cities are 1 percent smaller, compared to a drought-free counterfactual. I show that a positive correlation between drought and con-temporaneous city growth is misleading and that fully accounting for dynamic effects is essential to correctly understand the relationship between drought and city growth. Consistent with models that envision a drought-migration poverty trap, the negative effects on urbanization are more pronounced for the poorest countries.

Trade and pollution - Evidence from India (with Malin Niemi and Anna Tompsett).  

Abstract: What happens to pollution when developing countries open their borders to trade? Trade might increase production and thus pollution (the scale effect), increase incomes and thus demand for cleaner production (the technique effect), or shift production towards more or less clean industries (the composition effect). Empirical evidence on the environmental effects of trade liberalization in developing countries remains limited. We study the effects of the 1991 Indian trade liberalization reform on water pollution. We find that water pollution increased by 0.13 standard deviations per one standard deviation reduction in district-level tariff exposure.

60 years of global environmental change 1939-1999: digitization of 1.6 million historical aerial photographs (joint with Hannah Druckenmiller, Solomon Hsiang, Trinetta Chong, Shruti Jain, Andreas Madestam, Luna Yue Huang, Simon Greenhill, Joel Ferguson, Hikari Murayama, Sherrie Wang and Anna Tompsett).  

Abstract: Satellite imagery has transformed our understanding of both the natural world and human well-being, but the instrumental record only begins in 1972. We develop an approach to extend these data backwards in time an additional 30 years. We digitize the only complete archive of 1.6 million aerial photographs collected during the processes of mapping what was then the British Empire. This archive surveys more than 60 former colonies, where granular data from other sources is notoriously sparse, repeatedly from the 1940s to the 1990s. We develop a novel machine learning approach to assemble these photographs into mosaics comparable to modern satellite observations. We then generate large-scale, gridded datasets that provide measures of population density, land use, and infrastructure at 1km resolution.