When Floods Hit the Road – Impacts of rainy season flooding on transit and commuting in Kinshasa
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A rainy commute is unpleasant for most. But in many cities across Africa, a rainy season brings more than mere inconvenience. Especially where drainage and sewage systems are inadequate, rainfall can quickly result in flooded streets. Pedestrians are forced to take off shoes to trudge through murky waters. Overcrowded public transport experiences significant travel delays caused by impassable roads and slower driving speeds as drivers navigate flooded intersections and potholes of unknown depth. As urban mobility is obstructed, some people get cut off completely from their jobs and essential services. From Dar es Salaam to Kampala and Accra, these scenes are all too familiar in many cities – even under normal rainfall amounts.
Rainfall causes a substantial disruption to urban mobility.
But how do these disruptions impact individuals’ access to their jobs and urban economies as a whole? With support from the Global Facility for Disaster Reduction and Recovery, we decided to take a deeper look at this in Kinshasa, Democratic Republic of Congo. To do so, we teamed up with GoMetro to map and record Kinshasa’s public transport network, both under dry and rainy conditions. This effort involved surveyors riding along the city’s public transit routes, using the four main formal and informal public transport modes (Transco, Esprit de Vie, Esprit de Mort, and Taxi Jaune). Using an app-based data collection system, they recorded the origins and destinations of transit lines, the locations of stops, as well as the travel times between stops along the way. This effort generated transit feeds that are publicly available, which researchers and urban planners can use to improve the efficiency and resilience of Kinshasa’s public transit system.
We use these data to document the changes in itineraries, stop locations, vehicle frequencies, and travel speeds caused by the combination of water and bad road conditions. We find that while some public transport routes are unaffected, others see changes in itineraries both major and minor, including skipping stops or using different transport axes, impacting the commute of many. In addition, public transport vehicle headways increase on average by 13, 10, and 9 min for Esprit de Mort, Esprit de Vie, and Taxi Jaune vehicles respectively (between a 30% and 75% increase), while TRANSCO buses stopped operating. And average travel speeds decrease for all transit modes by up to 4 km/h, a 17% reduction.
Figure 1: Illustration of rerouting taking place as a result of rainy conditions on a Esprit de Mort itinerary
Economic costs amount to $1.2 million for each day of rain.
We then use this information to estimate the economic costs of transport disruptions from floods in Kinshasa. By using a 2018 commuter survey collected by the Japan International Cooperation Agency (JICA) we assess the origins and destinations of commuters, as well as their typical transport mode and socio-economic characteristics.
We find that on average, the share of jobs that can be reached within one hour, a commonly used metric to assess urban labor market physical integration, declines from 20% to 15% under rainy conditions, a 25% decrease. We also find that this average figure hides sizeable socio-spatial heterogeneities, with clusters of low-income residents incurring a large share of the travel delays caused by floods. This finding is especially important for public policy considerations to target disadvantaged groups and communities for in-kind and financial support.
Figure 2: Map of average travel delay aggregated to Traffic Analysis Zones (TAZs) (left panel) and income hot spot analysis on (right panel)
In aggregate, we estimate the city-wide economic costs caused by commuter travel delays for various flood intensities to be at least US$ 1.2 million per flood day – a number that should be multiplied by the number of days on which flooding is present. While these are substantial losses, they only partially measure the economic impacts of transport disruptions; for instance, they ignore infrastructure damages and the impacts on firms and supply chains. Instead, they focus exclusively on the losses incurred by households. It also downplays some of the increased detrimental effects from lower frequency/more intense rainy events.
Figure 3: Identifying the most critical links in Kinshasa’s road network to help prioritize upgrades
Our work doesn’t stop at assessing the problem; we also consider how resilience upgrades need to be prioritized to reduce disruptions most effectively. For all of Kinshasa, we identify the most critical transport links at risk of flooding and create the most extensive travel delays for commuters. In other words, we identify the road segments and intersections that are responsible for the highest economic losses and should be prioritized for upgrades. This information can help local decision-makers channel their resources – e.g., for public transport investment and road maintenance – where they will deliver the highest dividends in ensuring smooth urban mobility under normal and rainy conditions.
Full paper: He, Yiyi, Stephan Thies, Paolo Avner, and Jun E. Rentschler. 2020. “The Impact of Flooding on Urban Transit and Accessibility : A Case Study of Kinshasa.” World Bank Policy Research Working Papers, no. 9504: 1–31.