Sustainable Urbanization

Around three and a half billion people live in cities today and approximately five billion people are projected to live in cities by 2030. Though world's cities occupy just three percent of the Earth's land but they account for sixty to eighty percent of energy consumption. The urbanization of global citizens - the movement of residents from rural to urban regions - is exerting pressure everyday on potable water supplies, sewage, the living environment, and public health while also reshaping economies of our cities as they grapple to adapt.

In 2015, United Nations member states responded and adopted the 2030 Agenda for Sustainable Development, which includes seventeen connected goals aiming at a sustainable future for all. These goals concern sectors such as health, poverty, education, environment, and peace. The eleventh sustainable development goal, is known as “Sustainable Cities and Communities” and focuses on sustainable urbanization by envisioning cities and human settlements that are inclusive, safe, and resilient.

By 2050, almost three-quarter of the world population is predicted to live in urban settlements and the global demand for energy is likely to increase even more with this sudden inflow of people to urban areas. If cities do not prepare, the confluence of these two phenomenon will be detrimental to both the environment and the social conditions.

This project, housed within the Sustainable Urbanization Lab (SUL), tackles and explores what is driving urban growth trends through the use of data and media. Using natural language processing and studying Global sentiments we identify and map existing and emerging patterns as cities grow. We seek to understand cities and their changing resource demands using various lenses including political, environmental, and mobility in an effort to see how we can support and guide sustainable urbanization.

Project website

Does clean air increase the demand for the consumer city? Evidence from Beijing

Cities offer a large menu of possible employment and leisure opportunities. The gains from such consumer city leisure are likely to be lower on more polluted days. We study the association between daily consumption activity and outdoor air pollution in China and find evidence in favor of the hypothesis that clean air and leaving one's home for leisure trips are complements. Given the high levels of air pollution in cities in the developing world, regulation induced improvement in environmental quality is likely to further stimulate demand for the consumer city.

Air pollution and elite college graduates’ job location choice: evidence from China

In this paper, we examine the impact of air pollution on the job location choice of a highly educated labor force. Using the administrative job contract records of all graduates from Tsinghua University from 2005 to 2016, we find that air pollution significantly reduces the probability of elite graduates accepting job offers in a polluted city. Specifically, all else equal, if a city’s PM2.5 level increases by 10 μg/m3, the share of Tsinghua graduates choosing that city will decrease by 0.23 percentage point (9% of the mean value). This “crowding-out” effect is larger for master’s and doctoral graduates, but insignificant for undergraduates. A placebo test finds this effect does not exist for individuals who had signed a job contract prior to university admission, which strengthens our finding. Heterogeneity analysis indicates that males, students who grew up in cleaner provinces, and students graduating from school of the environment are more sensitive to air pollution. Different levels of preference for clean air and tolerance to pollution, as well as whether having the knowledge of pollution’s harms, can effectively explain the heterogeneous effect of air pollution’s impacts on job location choices of those elites.

Urban China's high level of ambient air pollution lowers quality of life and raises mortality risk. China's wealthy can purchase private products such as portable room air filters that offset some of their pollution exposure risk. Using a unique data set of Internet purchases, we document that households invest more in masks and air filter products when ambient pollution levels exceed key alert thresholds. Richer people are more likely to invest in air filters, which are much more expensive and more effective than masks. Our findings have implications for trends in quality of life inequality in urban China.

A 43-Million-Person Investigation into Weather and Expressed Sentiment in a Changing Climate

Understanding how the impacts of climate change are likely to modify individual well-being in the future is crucial for developing mitigation and adaptation strategies. Despite its importance, little is known about the day-to-day impacts of weather on individual subjective well-being in developing nations. To fill this gap, we use over 400 million geotagged posts across 43 million users from the social media Weibo in China, coupled with the meteorological conditions people face when posting, to estimate how climatic factors influence people's real-time expressed sentiment. We find that extreme weather worsens emotional expressions on social media. Females and individuals in poorer cities are more responsive to unpleasant temperatures. The centralized winter heating in North China effectively increases individuals' resilience against cold temperatures, whereas measures of air-conditioning prevalence do not show a substantial adaptation effect in summer. Our projections indicate the potentially harmful impacts of global warming on future subjective well-being.

Air pollution lowers Chinese urbanites’ expressed happiness on social media

High levels of air pollution in China may contribute to the urban population’s reported low level of happiness. To test this claim, we have constructed a daily city-level expressed happiness metric based on the sentiment in the contents of 210 million geotagged tweets on the Chinese largest microblog platform Sina Weibo4,5,6, and studied its dynamics relative to daily local air quality index and PM2.5 concentrations (fine particulate matter with diameters equal or smaller than 2.5 μm, the most prominent air pollutant in Chinese cities). Using daily data for 144 Chinese cities in 2014, we document that, on average, a one standard deviation increase in the PM2.5 concentration (or Air Quality Index) is associated with a 0.043 (or 0.046) standard deviation decrease in the happiness index. People suffer more on weekends, holidays and days with extreme weather conditions. The expressed happiness of women and the residents of both the cleanest and dirtiest cities are more sensitive to air pollution. Social media data provides real-time feedback for China’s government about rising quality of life concerns.

Exploring the effect of air pollution on social activity in China using geotagged social media check-in data

Understanding the complex impact of air pollution is crucial to assessing exposure risk and defining public health policies in China. However, the evidence and hence knowledge of how urban activity responds to air pollution are limited. In this paper, we propose to use geotagged check-in records on Weibo, a Tweeter-like platform, to systematically investigate the effect of air pollution on urban activity.

Based on panel models, we found clear evidence that such effect exists and varies between pollutants, visitors and residents, and different activity types. Typically, SO2 has the largest impact, followed by PM2.5, NO2, and PM10; local citizens' activities are more susceptible than visitors; leisure-related activity has a sensitivity at least twofold higher than work-related activities. Additionally, we tested hypotheses about the heterogeneous effect. We confirmed the role of Income and air quality, showing that people who live in richer and more polluted cities are more likely to experience the effects of air pollution. Specifically, people who live in a more polluted city with 100 unit increments in AvgAQI show on average the same sensitivity as those who live in a less polluted city and earn about 20.3 thousand yuan more in average Income.

This reveals new insights about environmental injustice in China. By presenting a portrait of the spatial heterogeneity, we argued that environmental injustice in terms of air pollution is not just about the difference in exposure risk measured based on population distribution, rather the measurement should also consider the disparity derived from urban activity. Secondly, new injustice may arise in underdeveloped areas where manufacture industry is transferred to but people barely take avoidance behavior. Finally, the map also reveals the general neglect of the detrimental effect of light air pollution, which we speculate is partly due to China's comparatively low standard in governmental regulations.

We believe our finding contributes significantly to exposure risk assessment and environmental justice debates. Hence it highlights the necessity and urgency of public healthy polices that spread the health consequence of air pollution, especially in the underdeveloped region.

Subway Expansion, Jobs Accessibility and Home Value Appreciation in Four Global Cities: Considering Both Local and Network Effec

We explore the potential of incorporating accessibility analysis in studying the impact of subway expansions on the real estate market. We first demonstrate that using increases in accessibility to firms as a continuous treatment variable instead of its binary alternative, the station-dummy approach, yields better goodness-of-fit in a quasi-experimental econometric analysis. We show that the dummy treatment variable consistently reported overestimated coefficients of impact for new subway stations. Furthermore, accessibility measures allow the exploration of impacts beyond the local effects around new subway stations, shedding light on network impact that has been largely overlooked in the literature. To provide greater external validity to our results, we apply the same analysis to the cities of Santiago (Chile), São Paulo (Brazil), Singapore, and Barcelona (Spain) and explore the common results. We argue that the integration of urban economics and transportation analysis can bring innovation to the empirical approach commonly adopted in the literature, and the use of accessibility measures in causal empirical studies on transportation impacts can produce more robust and comprehensive results and capture the nuanced spatial heterogeneity effects.

Subway Expansion and the Rise in the Spatial Disparity of Consumer Amenities

In this paper, we investigate how subway expansions have impacted the geographic concentration of consumer amenities within four global cities, namely Santiago, Singapore, Barcelona and São Paulo. Thereby, we delve into which neighborhoods benefit more and which suffer deficits from improved subway connectivity and their associated impacts upon local vibrancy. We found that originally vibrant communities in terms of consumer amenities benefit more than non-vibrant ones in terms of the attraction of new restaurants and shops. Further, we look into which accessibility destinations promoted by the subway expansion (e.g., accessibility to high-skill jobs or to affluents neighborhoods) result in the most significant effects. We show evidence that agglomeration economies are a relevant location driver mechanism that mediates the impact of accessibility improvements on the attraction of consumption activities. We also found to be evident that purchasing power of both workers and households matters as a market-access amenities location driver. Intra-city spatial concentration of economic activities, including consumption affairs, has been recognized as a longstanding urban phenomenon with implications on different dimensions within the urban planning domain. We discuss how much subway expansion increase or decrease such a spatial disparity of urban opportunities within the urban space.

Global air network and cross-border venture capital mobility

Using 23-year panel data of cross-border venture capital investment and global air network expansion as a natural experiment, this paper investigates the effect of air travel on cross-border capital mobility. We find international airlines have a significant facilitating effect on venture capital mobility. Based on the difference-in-differences estimate, for our research period one additional flight per day leads to an increase in VC investment between the city pair by 0.14 deals on average per year (1.08 times the mean value). The heterogeneous analysis indicates that, with more air connections, emerging industries and firms in earlier developmental stages receive more investment, and non-syndication investment increases more than syndication investment. In addition, we find the effect significantly increases with geographical distance: city pairs that are far away from each other experience a larger increase in VC flow after flight connections exist. Lastly, the evidence suggests that most of this increase in capital flows happens in wealthier cities. Connections between poor cities show little effect on VC flow. The paper presents evidence on the role of the global air network in reducing information transmission cost and raising the expectation for future growth potential. All results are shown to be robust using alternative VC investment measures and the regression discontinuity method.

How does urban agglomeration integration promote entrepreneurship in China? Evidence from regional human capital spillovers and

Using firm birth records and startup data matched with cities' characteristics, this paper analyzes nearly 300 prefecture-level cities to examine the role of human capital and market access in shaping the economic geography of innovation-driven entrepreneurship in China. We document strong positive entrepreneurial effects of local human capital resources and market size as well as market integration and human capital spillovers from mega-urban agglomerations of integrated cities. Our estimates point to an elasticity of innovation-driven entrepreneurship with respect to human capital spillovers of 0.50–0.79. The elasticity with respect to market integration is 0.53–0.89. Our results also suggest heterogeneous human capital spillover and market integration effects across urban agglomerations. These effects are more robust in first-tier urban agglomerations because first-tier urban agglomerations have a stronger economic base and greater connectivity. Strong human capital spillover and large gains from access to surrounding economic mass jointly highlight the integrated development of mega-urban agglomerations in China. We discuss policy implications that concern promotion of local innovation-driven entrepreneurship by strengthening intercity coordination, building transportation and social infrastructure, and improving urban management.