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As countries urbanize, human settlements are rapidly expanding into hazardous flood zones. This study provides a global analysis of spatial urbanization patterns and the evolution of flood exposure between 1985 and 2015. Using high-resolution annual data, it shows that settlements across the world grew by 85 percent to over 1.28 million square kilometers. In the same period, settlements exposed to the highest flood hazard level increased by 122 percent. In many regions, risky growth is outpacing safe growth, particularly in East Asia, where high risk settlements have expanded 60 percent faster than safe ones. Developing countries are driving the recent growth of flood exposure: 82 percent of the 36,500 square kilometers of settlements built in the world’s highest-risk zones since 1985 are in low- and middle-income countries. In comparison, recent growth in high-income countries has been relatively slow and safe. These results document a divergence in countries’ exposure to flood hazards. Rather than adapting their exposure to climatic hazards, many countries are actively increasing their exposure.

Transportation networks underpin socioeconomic development by enabling the movement of goods and people. However, little is known about how flooding disrupts transportation systems in urban areas in developing country cities, despite these natural disasters occurring frequently. This study documents the channels through which regular flooding in Kinshasa, the Democratic Republic of Congo, impacts transport services, commuters' ability to reach their jobs, and the associated economic opportunity costs from travel delays. This assessment is based on transit feed specification data sets collected specifically for this analysis under normal and flooded conditions. These data sets were combined with travel survey data containing travelers' socioeconomic attributes and trip parameters, as well as a high-resolution flood maps. The results show that (1) flood disruptions cause increases in public transit headways and transit re-routing, decreases in travel speeds, and thus travel time delays, which translate into substantial economic costs to local commuters; (2) accessibility to jobs decreases under flooded conditions, hindering the establishment of an integrated citywide labor market; (3) there are spatial clusters where some of the poorest commuters experience among the highest travel delays, highlighting socio-spatial equity aspects of floods; (4) certain road segments are critical for the transport network and should be prioritized for resilience measures; and (5) the estimated daily cost of flood disruption to commuters’ trips in Kinshasa is $1,166,000. The findings of this assessment provide disaster mitigation guidance to the Office des Voiries et Drainage under the Ministry of Infrastructure, as well as strategic investment recommendations to the Ministry of Housing and Planning.

This paper investigates the costs and benefits of three ex ante flood management strategies -- risk-based insurance, zoning, and subsidized insurance -- in an urban economics framework that takes land scarcity into account. In a theoretical setting and in the absence of market failures, risk-based insurance perfectly internalizes flood risks and maximizes social welfare. However, risk-based insurance faces major technical, social, and political challenges and is not always realistic. Flood zoning and subsidized insurance are two second-best options that are easier to implement and less technically demanding. The paper explores analytically and with numerical simulations the welfare losses and distributional impacts with these second-best options, and demonstrates that total losses often remain small. Flood zoning is close to optimal when flood-prone areas are small, floods are frequent, and housing quality is low. Zoning keeps total land value unchanged but transfers wealth from landowners in flood-prone areas to landowners in safe locations. Subsidized insurance is close to optimal when a large fraction of a city is flood prone, floods are rare, and housing quality is high. And although it increases flood losses through the moral hazard effect, subsidized insurance encourages more construction, which reduces housing rents and benefits tenants regardless of where they live. Subsidized insurance transfers wealth from landowners in safe locations to landowners in flood-prone areas. When the implementation of risk-based insurance is unrealistic, as is often the case in developing countries, a combination of zoning in high-risk areas and subsidized insurance for low-risk areas might be a good alternative.

This paper presents an analysis of transit accessibility to employment for 11 African cities. The use of identical methodologies and similar data sets allows for the creation of the first benchmark to compare accessibility across urban areas in Africa through different metrics and visuals. The study shows how the spatial pattern of land use and transport systems perform in connecting people to employment opportunities in these various settings. This first comparable benchmark is achieved by overcoming two significant data hurdles that are common in many developing country cities and in Africa in particular: (i) the scarcity of information on the distribution of employment and (ii) the lack of information on transit routes and travel times. These data gaps are filled through a novel methodology to estimate the distribution of employment in urban areas (Employment Opportunity Areas) as well as a comprehensive mapping of informal transit networks. The analysis developed here can be replicated in different cities in the future. The computation of these baseline accessibility studies also opens up the possibility to assess the impacts of future transport investments and/or land use changes, through the use of counterfactual scenarios, which could assist decision makers in these cities. Finally, this analysis can serve as a demonstration that the computation of accessibility metrics is achievable, including in data scarce environments, and should be considered as a progress indicator for Sustainable Development Goal 11.2, which focuses on safe and affordable transport for all, including public transport.

This review examines the literature on the welfare impacts of infrastructure disruptions. There is widespread evidence that households suffer from the consequences of a lack of infrastructure reliability, and that being connected to the grid is not sufficient to close the infrastructure gap. Disruptions and irregular service have adverse effects on household welfare, due to missed work and education opportunities, and negative impact on health. Calibrating costs of unreliable infrastructure on existing willingness to pay assessments, we estimate the welfare losses associated with blackouts and water outages. Overall, between 0.1 and 0.2 percent of GDP would be lost each year because of unreliable infrastructure -- electricity, water and transport.

The inter-connectedness of workers’ residential locations and job opportunities is a key determinant of labor market outcomes. This study provides an analysis of the spatial distributions of job accessibility, housing rents, and poverty in a large African city. In Nairobi, Kenya, workers and jobs are not well connected: On average, residents can access fewer than 10 percent of existing jobs by foot within an hour. Even using a minibus, they can reach only about a quarter of jobs. This study further demonstrates that poorer households and residents living in informal settlements are even more limited. Living closer to job opportunities is costly in Nairobi. Not only are housing quality and living conditions frequently better in such areas, but the high value placed on job accessibility also makes these areas more expensive. This severely affects the residential location choices of low-income households.

Although climate scientists explore the effects of climate change for 2100, it is a challenging time frame for urban modellers to foresee the future of cities. The question addressed in this paper is how to improve the existing methodologies in order to build scenarios to explore urban climate impacts in the long term and at a fine scale. This study provides a structural framework in six steps that combines narratives and model-based approaches. The results present seven scenarios of urban growth based on land use strategies and technological and socio-economic trends. These contrasted scenarios span the largest possible world of futures for the city under study. Urban maps for 2010, 2040 and 2100 were used to assess the impacts on the Urban Heat Island. The comparison of these scenarios and related outputs allowed some levers to be evaluated for their capacity to limit the increase of air temperature. Narrative scenarios of urban change are flexible and highly imaginative.Model-based scenarios of urban change allow for quantitative environmental assessment.A six-step method provides a framework for combining and benefiting from both approaches.Contrasting scenarios of urban change and their impacts on Urban Heat Island are simulated.The comparison of scenarios provides insights into key triggers to improve urban adaptation.

Whether individuals and job opportunities are well connected is a key determinant of productive urban labor markets. The overall level of job accessibility in a city depends on the locations of jobs and workers' residences, as well as transport networks. Moreover, who has good access to job opportunities hinges on the trade-off faced by households in their residential choices over job accessibility, living conditions, and housing costs. This paper empirically analyzes the spatial distributions of job accessibility, housing rents, and poverty in Nairobi, Kenya. It finds that workers and jobs are not well connected in the city: Nairobi residents can on average access fewer than 10 percent of existing jobs by foot within an hour. Even using a minibus, they can reach only about a quarter of the jobs. This paper further shows that poorer households and/or those who live in informal settlements can reach a more limited number of jobs. Living closer to job opportunities is indeed costly in Nairobi, not only because housing quality and living conditions tend to be better in such areas, but also job accessibility itself is valued as a great amenity in the housing markets, which challenges low-income households' residential location choice.

Transit subsidies in the urban area of Buenos Aires are high, amounting to a total of US$5 billion for 2012. They have been challenged on several counts: suspected of driving urban sprawl and associated infrastructure costs, diverting resources from system maintenance, and failing to reach the poor among others. In this context, this paper examines the impacts of cost recovery fares under a range of different policy scenarios that could cushion the impact of fare increases. The alternative scenarios that are scrutinized are the uncompensated removal of the transit subsidy, its replacement by a lump sum transfer, and its replacement by two different construction subsidy schemes. Using a dynamic urban model (NEDUM-2D) calibrated for the urban area of Buenos Aires, all scenarios are assessed along four dimensions: (i) the efficiency/welfare impact on residents, (ii) the impacts on the internal structure of the urban area and sprawl, (iii) the impact on commuting-related carbon dioxide emissions, and (iv) the redistributive impacts, with a focus on the poorest households. A series of results emerge. First, there are consumption-related welfare gains for residents associated with replacing the transit subsidy by a lump sum transfer. Second, there are only moderate reductions in urbanization over time and thus infrastructure costs associated with the subsidy removal. Third, the replacement of the transit subsidy leads to only moderate increases in carbon dioxide emissions despite lower public transport mode shares, because households will chose to settle closer to jobs, thereby reducing commuting distances. Finally, the replacement of the transit subsidy by a lump sum transfer will lead to short-term harsh redistributive impacts for captive transit users in some areas of the urban area. Medium-term adjustments of land and housing prices will partially mitigate the negative impacts of higher transport costs for tenants, but will further hurt homeowners.

National audience; Le Versement pour Sous Densité est une mesure innovante qui a fait son entrée dans la loi française depuis mi-2012 et qui vise à limiter l’étalement urbain en taxant les nouvelles constructions qui n’atteignent pas un Seuil minimal de densité. Ce papier, à travers l’utilisation d’un modèle transportusage des sols (NEDUM 2D), quantifie les impacts potentiels de cette politique sur l’Ile-de-France et examine les conditions qui lui permettraient de gagner en efficacité tout en limitant les coûts sociaux de sa mise en œuvre. Les résultats de cette étude montrent que si cet outil est correctement utilisé, il peut contribuer à limiter l’étalement urbain tout en augmentant les surfaces construites et donc en diminuant le niveau des prix immobiliers et des loyers. De façon surprenante, il s’agit donc d’une taxe sur la construction qui a pour résultat un accroissement des surfaces des logements. Cependant la mise en œuvre de cette politique est compliquée puisque le choix du Seuil minimal de densité en conditionne largement l’efficacité. Si celui-ci est trop bas le versement peut avoir des impacts contre-productifs comme une accélération de l’étalement urbain. De plus, en fonction de l’objectif privilégié (limitation de l’étalement urbain, accès aux transports en commun, …), le choix du seuil optimal variera.

Well-functioning cities reduce the economic distance between people and economic opportunities. Cities thrive because they enable matchmaking -- among people, among firms, and between people and job opportunities. This paper examines employment accessibility in Nairobi, Kenya and evaluates whether modification of land use patterns can contribute to increases in aggregate accessibility. The assessment is based on simulation of counterfactual scenarios of the location of jobs and households throughout the city without new investments in housing or transport infrastructure. The analysis finds that modifications to the spatial layout of Nairobi that encourage land use clustering can increase the share of overall opportunities that can be accessed within a given time-frame. When commuters travel by foot or using the minibus network, the share of accessible economic opportunities within an hour doubles from 11 to 21 percent and from 20 to 42 percent respectively. The analysis also finds that spatial layouts that maximize the number of households that have access to a minimum share of jobs, through a more even jobs-housing balance, come at the expense of average accessibility. This result is interpreted as a trade-off between inclusive and efficient labor markets.

L’objectif de cet article est d’evaluer les apports et les limites d’usage des modeles SLEUTH, LCM et NEDUM-2D pour spatialiser des scenarios prospectifs d’amenagement du territoire. Les deux modeles de changements d’occupation et d’usage des sols spatialement explicites SLEUTH et LCM sont bases sur une approche inductive de simulation de patrons spatiaux tandis que NEDUM-2D est un modele economique d’expansion urbaine a base de processus. L’application porte sur l’aire urbaine de Toulouse dont les trajectoires d’evolution des changements d’occupation et d’usage des sols entre 1990 et 2006 ont prealablement ete reconstruites. Le but est de suivre la dynamique spatio-temporelle de l’expansion urbaine et de calibrer les deux modeles SLEUTH et LCM. Apres une presentation detaillee de la demarche methodologique de construction de scenarios contrastes, coherents et plausibles de developpement urbain, le fonctionnement et les hypotheses propres a chacun des trois modeles de spatialisation sont presentes. Ensuite, une analyse comparative des resultats des deux modeles SLEUTH et LCM est menee a travers la spatialisation d’un scenario tendanciel elabore a l’horizon 2025. Les resultats obtenus montrent d’importantes differences entre les simulations issues des deux modeles. L’influence de ces derniers concerne a la fois la quantite de changement et son allocation spatiale. Les resultats indiquent aussi que les deux modeles empiriques SLEUTH et LCM, calibres a l’aide des trajectoires passees, ne permettent pas de spatialiser des scenarios de rupture avec les tendances passees. A l’issue de cette analyse, nous proposons de developper un nouveau modele hybride couplant l’approche economique et l’approche geographique, utilisable de facon controlee conformement a la definition de scenarios normatifs.

This paper investigates the effect of carbon or gasoline taxes on commuting-related CO2 emissions in an urban context. To assess the impact of public transport on the efficiency of the tax, the paper investigates two exogenous scenarios using a dynamic urban model (NEDUM-2D) calibrated for the urban area of Paris: (i) a scenario with the current dense public transport infrastructure, and (ii) a scenario without. It is shown that the price elasticity of CO2 emissions is twice as high in the short run if public transport options exist. Reducing commuting-related emissions thus requires lower (and more acceptable) tax levels in the presence of dense public transportation. If the goal of a carbon or gasoline tax is to change behaviors and reduce energy consumption and CO2 emissions (not to raise revenues), then there is an incentive to increase the price elasticity through complementary policies such as public transport development. The emission elasticity also depends on the baseline scenario and is larger when population growth and income growth are high. In the longer run, elasticities are higher and similar in the scenarios with and without public transport, because of larger urban reconfiguration in the latter scenario. These results are policy relevant, especially for fast-growing cities in developing countries. Even for cities where emission reductions are not a priority today, there is an option value attached to a dense public transport network, since it makes it possible to reduce emissions at a lower cost in the future.

L'urgence climatique appelle des politiques de réduction de gaz à effet de serre ambitieuses. Depuis la mise en oeuvre du protocole de Kyoto les avancées sont réelles avec notamment la création du marché carbone européen (EU ETS) pour les entreprises fortement émettrices. Cependant, il apparaît aujourd'hui que cette direction ne peut à elle seule suffire à placer les économies sur des sentiers de croissance suffisamment vertueux. Dans ce contexte, les villes qui sont les hôtes principaux des populations (plus de 50% de la planète vit en zone urbaine depuis 2007) et des activités consommatrice d'énergie (transport, bâtiment...), apparaissent comme une « nouvelle » aire d'investigation pour les politiques climatiques constituant d'immenses potentialités de réduction de gaz à effet de serre. De nombreux territoires sont convaincus de leur rôle fondamental dans la bataille du climat et tendent à se regrouper et à s'engager dans des plans climat locaux que des éclairages scientifiques pourraient contribuer à rendre plus efficaces. L'émergence de la ville / du territoire comme niveau approprié de mise en oeuvre des politiques climatiques, impose aux chercheurs de renouveler outils et approches méthodologiques afin de pouvoir rendre compte des nouvelles options techniques et organisationnelles et éclairer la décision politique. Ce chapitre explore les pistes d'amélioration possibles des outils de prospective dans le domaine énergie – climat, pour apporter aux collectivités territoriales des éclairages appropriés à des politiques climatiques locales plus ambitieuses.