River flooding - Cities and FUAs

This dataset provides indicators of population and built-up exposure to river floods.

Data sources and methodology

River flooding indicators are estimated using the River Flood Hazard Maps at European and Global Scales datasets (Dottori, F. et al., 2021), which provide the extent of river floods for different return periods (10 to 100 years). A return period corresponds to the estimated time interval between floods of similar intensity. For OECD countries located in Europe and the Mediterranean Basin, the regional 250-metre resolution map was used. For the remaining OECD countries, the global map with a spatial granularity of 1 km was used. Built-up area exposure to river floods is computed by intersecting this map with Copernius annual land cover data (Copernicus Climate Change Service, Climate Data Store, 2019) and population exposure is computed using the Global Human Settlement Population layer (European Commission, GHSL Data Package 2023). Harmonised international hazard models are used to ensure global comparability, consistent modelling assumptions across countries, and complete subnational coverage.

These estimates may differ from official subnational flood risk statistics due to differences in methodological approaches - such as the use of global, modelled top down hazard maps versus national hydrological models or administrative flood zone delineations - as well as variations in input data sources, spatial resolution, and hydraulic modelling techniques.

Defining FUAs and cities

The OECD, in cooperation with the EU, has developed a harmonised definition of functional urban areas (FUAs) to capture the economic and functional reach of cities based on daily commuting patterns (OECD, 2012). FUAs consist of:

1. A city – defined by urban centres in the degree of urbanisation, adapted to the closest local administrative units to define a city.


2. A commuting zone – including all local areas where at least 15% of employed residents work in the city.

The delineation process includes:

• Assigning municipalities surrounded by a single FUA to that FUA.


• Excluding non-contiguous municipalities.

The correspondence table between SAUs and FUAs/cities is available in parquet and csv format.

The definition identifies 1 272 FUAs and 1 269 cities in all OECD member countries except Costa Rica and three accession countries.

Cite this dataset

OECD Regions, cities and local areas database (River flooding - Cities and FUAs), http://oe.cd/geostats

Further information

• OECD Local Data Portal


• OECD Regions and Cities at a Glance

For questions and/or comments, please email [email protected]