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River flooding - Cities and FUAs

<p align="justify">This dataset provides indicators of population and built-up exposure to river floods.</p>

<h3>Data sources and methodology</h3> <p align="justify"> River flooding indicators are estimated using the River Flood Hazard Maps at European and Global Scales datasets <a href=https://doi.org/10.2905/1D128B6C-A4EE-4858-9E34-6210707F3C81>(Dottori, F. et al., 2021)</a>, 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 <a href=https://doi.org/10.24381/cds.006f2c9a>(Copernicus Climate Change Service, Climate Data Store, 2019)</a> and population exposure is computed using the Global Human Settlement Population layer <a href=https://doi.org/10.2760/098587>(European Commission, GHSL Data Package 2023)</a>. Harmonised international hazard models are used to ensure global comparability, consistent modelling assumptions across countries, and complete subnational coverage. </p>

<p align="justify">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. </p>

<h3>Defining FUAs and cities</h3> <p align="justify">The OECD, in cooperation with the EU, has developed a harmonised <a href="https://www.oecd.org/en/data/datasets/oecd-definition-of-cities-and-functional-urban-areas.html">definition of functional urban areas</a> (FUAs) to capture the economic and functional reach of cities based on daily commuting patterns <a href=https://doi.org/10.1787/9789264174108-en>(OECD, 2012)</a>. FUAs consist of: <ol> <li><b>A city</b> – defined by urban centres in the degree of urbanisation, adapted to the closest local administrative units to define a city.</li> <li><b>A commuting zone</b> – including all local areas where at least 15% of employed residents work in the city.</li> </ol> The delineation process includes: <ul> <li>Assigning municipalities surrounded by a single FUA to that FUA.</li> <li>Excluding non-contiguous municipalities.</li> </ul> The correspondence table between SAUs and FUAs/cities is available in <a href=https://webfs-cfe.oecd.org/files/.Stat/cities_local_areas/fua_cities_sau_mapping.parquet>parquet </a> and <a href=https://webfs-cfe.oecd.org/files/.Stat/cities_local_areas/fua_cities_sau_mapping.csv>csv</a> format.

The definition identifies 1 272 FUAs and 1 269 cities in all OECD member countries except Costa Rica and three accession countries.</p> <h3>Cite this dataset</h3> <p>OECD Regions, cities and local areas database (<a href="http://data-explorer.oecd.org/s/1d9 ">River flooding - Cities and FUAs</a>), <a href=http://oe.cd/geostats>http://oe.cd/geostats</a></p>

<h3>Further information</h3> <ul> <li> <a href=https://localdataportal.oecd.org/>OECD Local Data Portal </a> </li> <li> <a href=https://www.oecd.org/en/publications/oecd-regions-and-cities-at-a-glance-2024_f42db3bf-en.html/>OECD Regions and Cities at a Glance </a> </li> </ul> <p align="justify">For questions and/or comments, please email <a href="mailto:CitiesStat@oecd.org">CitiesStat@oecd.org</a>