# 1. Introduction

In all parts of the world, cities are providing jobs and improved livelihoods to an ever growing number of people. Through the density of social and economic activity, people living in or moving to cities gain easy access to services, jobs, and markets. Analogously, firms benefit from facilitated access to large and diverse labor markets. The benefits from spatial proximity are made possible through infrastructure systems that increase connectivity and efficiency. Transport infrastructure for example connects people to markets and jobs, and connects firms to suppliers, consumers, and markets. In providing the backbone of most economic activity, infrastructure systems thus play a crucial role for anything from meeting the basic needs of people, to supporting sustainable and resilient livelihoods and enabling ambitious economic endeavors.

However, the functioning of infrastructure and the urban economy can be threatened by natural hazards. Urban flooding in particular is a major cause of disruptions in cities across the world, and especially in developing countries. From Buenos Aires to Dar es Salaam, Amman, Dhaka, and Jakarta – around the world, urban flooding is a frequent and devastating occurrence, and the resulting disruptions extend well beyond just the flood-zone. Of course, urban flooding is directly damaging public assets, affecting people’s homes and assets, and destroying the productive assets of firms. But beyond the direct impacts, floods are also causing knock-on effects on infrastructure networks well beyond the flooded areas. As one road segment is flooded, traffic across the entire city is disrupted, thus affecting people’s access to jobs and the smooth functioning of supply chains. The indirect costs of urban flooding are real and often significant.

In order to better assess this threat, this analysis addresses three topics. First, it analyses how economic activity and road transportation infrastructure is exposed by urban flood risk. Second, the network-level effects of floods on urban connectivity and accessibility are assessed. Finally, it investigates whether flood risk affects infrastructure disruptions at the level of an individual firm. To address these questions, flood maps, employment density maps, infrastructure maps, and geocoded firm-level micro data is used for the 13 cities of Abidjan, Accra, Addis Ababa, Bamako, Cotonou, Douala, Dar es Salaam, Freetown, Kampala, Kigali, Monrovia, Nairobi, and Zanzibar.

The analysis finds that a significant fraction of economic activity is exposed to flood risk – though the level exposure varies significantly across cities. In Kampala, about 10% of all jobs are directly located in flood risk zones. Indeed, large fractions of the road network in these cities are located in areas that are potentially prone to flooding, often with depths that make traversing the roads impossible. In Kampala, hydrological flood models estimate flood depths at several road segments to exceed one meter (or three feet). Moreover, the impacts of flooding are felt not only in directly exposed flood zones, but across the entire city. Connectivity between firms is estimated to be affected significantly with travel times more than doubling for a quarter of all firms. Urban flooding is also estimated to make hospitals inaccessible to a third of all locations within the “golden hour”, i.e. the 60 minutes window following a critical medical incident beyond which survival rates are reduced drastically.

The remainder of this study is structured as follows. Section 2 outlines the types of data that are crucial to conduct city level hazard assessments, including high-resolution flood maps, and open source infrastructure network data. Section 3 presents evidence from a pooled dataset of up to 3,000 firms from 13 major cities in Sub-Saharan Africa, showing that infrastructure disruptions are transmitted across citywide networks and affect firms in- and outside of flood zones. Section 4 applies a geospatial network analysis tool to assess the direct exposure of jobs, road networks, and urban connectivity. Section 5 concludes.

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