Methods for Analyzing the Mobility Impacts of Urban Flood Events

2020

English

Urban flooding as a result of high-intensity rain events is common in many cities. This is also the case in the Accra Metropolitan Area where the rapid and extensive urban development of recent years has increased the frequency and severity of urban flooding because many natural water ways have been partly blocked or restrained by new houses and infrastructure. The objective of the CLIMACCESS Work Package C is to spatially analyze the vulnerability of the transport system within the context of the current urban development practices and the rapid urban expansion using novel applications of GIS network tools. The aim is to analyze how and where flooding events directly affect the transport network by reducing or temporarily removing network connectivity at certain locations, and how this further affects levels of mobility and accessibility in different urban areas. While flooding in the urban areas presents numerous problems for the affected urban population, this report focus specifically on GIS-based methods for analyzing the effects that floods potentially have on the overall physical mobility within Accra. In this context, the mobility is defined as daily or frequent trips to specific other parts of the urban region and to central Accra which is common to many residents' livelihood strategies. By linking GIS-based mobility/accessibility analysis with the flood predictions maps resulting from CLIMACCESS Work Package B we are able to produce new ‘vulnerability maps’ of the transport network in different parts of the city area as well as spatial predictions of accessibility and mobility levels under future flood scenarios. In this way, the described spatial analysis methods can assist in the identification of vulnerable ‘gateway’ locations in the Accra area that are characterized by a high risk of flooding as well as a position in the transport system that affects the mobility of a large part of the population. The methods can furthermore be applied to assess how the magnitude of the rain events influences the mobility situation. The report details how to produce maps that show where floods are most likely affect the transportation network and to calculate the cost in terms of number of potentially affected people for each individual flood location. This information is relevant for infrastructure planning and decisions about where to initiate efforts to reduce the frequency and magnitude of flooding.

Allotey, A. N.; Fog, B.; Kofie, R. Y.; Møller-Jensen, L.