Methodology to support cities on measuring their safeguarding from flooding

With climate change impacts increasingly affecting cities, the C40 Cities Climate Leadership Group (C40) is implementing a global project to support their member cities in assessing their climate safeguarding, a key step in building climate-resilient cities. Under this project, OneWorld was contracted to develop a methodology that C40 member cities can use to undertake self-assessments of their solutions to safeguard against flood damage.

OneWorld carried out a synthesised literature review and developed a database of available flood safeguarding methods and best practice. This allowed the identification of a set of five broad categories of safeguard actions recommended for African cities, in terms of their feasibility (ease of implementation), availability of data (e.g. costs and benefits) and availability of datasets; and their impact on people – a key factor. Safeguard categories identified included urban watershed and river flood management, urban drainage water system management, and coastal flooding management. In addition, Early Warning Systems and Flood forecasting are cross-cutting actions.

The project team then developed a GIS methodology to assess flooding risk and vulnerability (including identifying the most vulnerable and exposed areas in terms of both flooding and vulnerability of the population). The methodology enables gauging the impacts of flood management actions and facilitates decision-making in safeguarding these cities from floods. The methodology was tested with two African cities, one coastal and one inland, to provide lessons learned and best practices for broader application.

The final part of this project was developing a risk and vulnerability (RVA) tool for policy makers. The RVA tool assists cities to identify the best safeguards for their respective cities. It calculates the cost benefits of avoided impacts attained through implementing given flood safeguard actions and applies mixed methods to calculate the impact of floods on vulnerable populations, in terms of the safeguard measures being applied by cities. It draws on data from the GIS mapping to quantify the associated impacts on cities. The objective is to enable users to assess and determine which of the flood safeguarding actions will have the greatest mitigating impact on people and buildings in the city concerned. It was developed such that the different safeguard measures are tailored for each city.