“Cholera Forcing” and the Urban Water Infrastructure: Lessons from Historical Berlin
Did cholera function as a potent catalyst for the reform of urban water infrastructure in 19th century Europe's disease-ridden cities, serving as “our old ally” in the struggle for urban sanitation (Robert Koch)? Based on a detailed case study of Berlin's hydrological reconfiguration, this paper challenges popular narratives that paint the emergence of safe tap water supplies and sanitary sewers as an efficient, scientifically motivated reaction to Europe's recurrent cholera epidemics since 1831. While historians have long stressed the dominance of aesthetical and industrial over sanitary concerns, the study of Berlin' contemporary discourse suggest that the causal link between cholera and water infrastructure reform was not only weak, but ambiguous. Far from motivating the right actions for the wrong reasons, cholera's conception through the dominant miasmatist frameworks and limited proto-epidemiological tools of the pre-bacteriological era inspired inefficient, at times even counterproductive approaches that potentially deepened the urban mortality penalty. Berlin's role as a political and scientific center of 19th century Europe suggests that her experience was the norm rather than the exception. A nuanced understanding of Western Europe's sanitary past has important implications for the continuing struggle for urban sanitation in today's developing world.
Covid-19 across European Regions: The Role of Border Controls
Attempts to constrain the spread of Covid-19 included the temporal reintroduction of travel restrictions and border controls within the Schengen area. While such restrictions clearly involve costs, their benefits have been disputed. We use a new set of daily regional data of confirmed Covid-19 cases from the respective statistical agencies of 18 Western European countries. Our data starts with calendar week 10 (starting 2nd March 2020) and extends to calendar week 17 (ending 26th April 2020), which allows us to test for treatment effects of border controls. We use Poisson models with fixed effects and controls for the stringency of national measures, as well as a Bayesian spatio-temporal specification using an integrated nested Laplace approximation (INLA) to take unobserved spatio-temporal heterogeneity into account. Both approaches suggest that border controls had a significant effect to limit the pandemic.
Persistent Shocks to Urban Density: Evidence from the Berlin Air Raids
Temporary shocks can have persistent effects on the distribution of economic activity across urban space, suggesting considerable “stickiness” in adjustment to spatial equilibrium. I examine the long-run effect of World War II air raids on Berlin’s contemporary population density profile, exploiting random variation in the extent of damage caused at the scale of street blocks, while controlling for a flexible, secular time trend in the citywide density gradient. 70 years after the end of the war, blocks affected by irreparable damage feature significantly lower population density, while repairable damage had no lasting effect. These findings are consistent with a vintage effect, where large fixed costs associated with the construction of new buildings retard adjustment of the housing supply to growing demand for low-density structures.
Dense, Diverse and Healthy? Mixed-Income Housing and the Spread of Urban Epidemics
During the second half of the 19th century, the incidence of infectious and epidemic diseases declined dramatically across Western cities. While contemporary observers agreed that changes to the social geography of densifying cities were a fundamental driver of this urban health transition, the spread of mixed-income housing gave rise to controversial debate. Proponents of social mixing anticipated the New Urbanist case for local desegregation, expecting substantial benefits from the transmission of health-conducive norms, shared use of sanitary infrastructure, and access to informal help-in-kind networks within diverse buildings. Critics warned that mixed-income housing undermined traditional social barriers and exposes residents to a more diverse set of disease vectors, thus facilitating the spread of epidemics across all classes of urban society. While the social mixing controversy played a central role in the 19th century housing reform discourse, the interplay of increasing diversity and declining epidemic incidence during the urban health transition has not been systematically explored.
Filling this gap, this paper provides causal estimates of the effect of social diversity on epidemic incidence from the universe of buildings in Berlin in 1866 – the year of the most lethal cholera outbreak in what was arguably 19th century Europe's most diverse urban environment. Adaption of the biological concept of species diversity and a mapping of the occupations of roughly 89,000 household heads listed in the 1866 town directory to a social stratification scale provide a building-level measure of social diversity. Conditional on a wide range of risk factors, and exploiting exogenous variation from building lots' geometric properties in a non-linear control function approach, social diversity has an ambiguous effect on cholera incidence: A one-standard-deviation increase in diversity results in a 26 percentage points higher risk of initial incidence (which is about the citywide a priori probability of incidence, 26.5 %), and a .5 percentage points drop in the case rate among affected buildings (11 % of the mean case rate, 4.5 %). These competing margins roughly cancel each other out on average, resulting in a close-to-zero overall effect. Results are robust to a variety of sensitivity checks, controls for spatial auto-correlation and alternative measures of diversity.
A plausible interpretation is that diversity increases a residential community's probability to contract infectious diseases from outside vectors, while also providing additional means to confine further in-house spread – meaning that both critics and supporters of social mixing had a point. A causal mediation framework quantifies the importance of four potential underlying mechanisms. Most importantly, mediation analysis reveals that diversity and the number of infected neighbors living close-by strongly interact in increasing the risk of initial infection, while bearing little effect along the intensive margin. In contrast, about 10 % of the incidence-reducing effect of diversity on the intensive margin is attributable to mediation via shared sanitary infrastructure in the form of building-wide tap water access.
Sanitation, Externalities and the Urban Mortality Transition
During the late 19th and early 20th centuries, the roll-out of tap water and sewerage infrastructure contributed to a dramatic mortality decline in Western cities. However, recent studies show that substantial health benefits only materialized after both systems were in joint operation, whereas the isolated introduction of tap water infrastructure offered little benefit and could even increase mortality before the advent of sanitary sewers. This paper offers an explanation based on a negative externality arising from spatio-temporal disparity in the roll-out of tap water and sewerage networks within a city. Access to a cheap, reliable and pressurized fresh water source allows individuals to clean up their local environment by flushing away liquid and solid waste. While this results in direct health benefits, the emission of pathogens to streets, gutters, ground water acquirers and open water bodies imposes indirect costs on neighbors located along the spatial trajectory of the resulting waste flows. As a result, city-level mortality does not necessarily decrease monotonously in the roll-out of tap water infrastructure. Sanitary sewers neutralize the externality, thus yielding social benefits on top of any direct gains for connecting households.
I test this mechanism using a newly constructed dataset of all roughly 14,300 buildings in Berlin, observed in 1875 and 1880 – a crucial five-year period during which the city's mortality rate dropped by almost 20 %, while the share of buildings connected to the tap water and sewerage networks increased from 59 to 84 % and 0 to 55 %, respectively. Based on a digital terrain model and its implied flow direction matrix, I trace the spatial trajectory of waste flows, thus directly measuring the impact of the health externality. In a difference-indifferences PPML specification, I find that a building’s crude death rate (CDR) drops by .085 and .168 percentage points after obtaining tap water and sewerage, respectively – accounting for 13 and 26 % of the total CDR decline between 1875 and 1880. On top of these direct benefits, a one-standard-deviation drop in waste flow exposure decreases the CDR by .067 percentage points or 11 % of the total CDR decline. I show that the implied aggregate net effects are consistent with recent city-level studies. Exploiting sharp cut-offs in the roll-out of sewerage across Berlin’s main water bodies, I report consistent results from a complimentary regression discontinuity design.
Using building-level occupational data, I explore the distribution of direct benefits and indirect costs across the income distribution. In line with long-standing claims in the qualitative literature, I find that the benefits from pre-sewerage tap water infrastructure were biased in favor of the affluent, thus widening the socioeconomic health gap. Rather than closing this gap, the roll-out of sewerage further widened urban health inequality. Based on counter-factual analyses, I conclude that there was no feasible alternative policy that would have brought about similar average health benefits while reducing both socioeconomic health inequality and exposure to waste flows. The paper concludes with a discussion of the role of private and public sanitary infrastructure provision during the Western historical mortality transition.