A transparent framework for comparing river, surface-water, coastal and climate-related flood susceptibility in Porto, Matosinhos, Viseu, Valpaços, Marinha Grande, Évora and Bragança.
The dashboard is a comparative city-scale screen. It combines evidence for river flooding, surface-water or flash flooding, coastal flooding and climate-related amplification. Porto has the highest combined susceptibility because three credible pathways coincide: the Douro estuary, intense-rainfall drainage stress and Atlantic overtopping. Matosinhos also has a multi-pathway profile. Bragança ranks third because Portugal’s environmental authority has proposed a combined fluvial/pluvial significant-risk area on the Rio Fervença.
| Rank | City | Index | Band | Fluvial | Pluvial / flash | Coastal | Climate |
|---|---|---|---|---|---|---|---|
| 1 | Porto | 81 | Very high | 4 | 4 | 3 | 5 |
| 2 | Matosinhos | 69 | High | 3 | 4 | 3 | 4 |
| 3 | Bragança | 51 | High | 3 | 3 | 0 | 3 |
| 4 | Viseu | 43 | Moderate | 2 | 3 | 0 | 3 |
| 5 | Marinha Grande | 42 | Moderate | 2 | 2 | 0 | 4 |
| 6 | Évora | 35 | Moderate | 1 | 3 | 0 | 3 |
| 7 | Valpaços | 30 | Moderate | 1 | 2 | 0 | 3 |
The European Flood Awareness System, or EFAS, provides European overviews of ongoing and forecast floods up to ten days ahead. It is an operational awareness and forecasting system rather than a long-term parcel-risk map.1
The Joint Research Centre global river-flood dataset provides modelled water depth at 90 m resolution for seven return periods from 10 to 500 years. The source states that it is not an official flood-hazard map and excludes small islands and river basins below 500 km².2 The peer-reviewed European predecessor identifies further limitations, including omitted flood defences, omitted rivers with upstream areas below 500 km², and difficulty representing channels and lowland topography.3
The national reference is the Agência Portuguesa do Ambiente (APA). Under the European Floods Directive, APA identifies Areas of Potentially Significant Flood Risk, known as ARPSI, prepares flood-hazard and flood-risk maps, and develops six-year Flood Risk Management Plans.4 The second-cycle process identified 63 ARPSI in mainland Portugal and includes fluvial, pluvial and coastal mechanisms.5
Each component uses an ordinal evidence score. Zero means that no meaningful pathway was established. One indicates low or limited evidence. Two indicates a locally relevant pathway. Three indicates a material pathway. Four indicates high susceptibility. Five indicates very high, recurrent or extensive susceptibility. The climate-outlook score represents the strength of authoritative evidence for future amplification through approximately 2050–2100.
| Index | Band | Intended interpretation |
|---|---|---|
| 0–24 | Low | Limited evidence of meaningful city-scale susceptibility in the reviewed sources. |
| 25–49 | Moderate | One or more locally relevant pathways, but evidence is spatially limited, indirect, or not a current significant-risk designation. |
| 50–74 | High | Multiple material pathways or an official/proposed significant-risk area with substantial supporting evidence. |
| 75–100 | Very high | Several high-susceptibility pathways with strong official and local evidence, including a strong future amplification signal. |
The weights emphasize present-day river and surface-water pathways while retaining explicit coastal and future-climate dimensions. They are analytical choices for comparison. They are not APA or EFAS weights.
Porto occupies the lower Douro estuary and includes the Atlantic frontage at Foz. APA identifies the Porto–Vila Nova de Gaia river ARPSI and Porto–Foz coastal ARPSI. The municipal assessment also identifies urban drainage vulnerability and raises late-century fluvial risk and coastal overtopping within its scenario framework.7 8
The lower Rio Leça, dense urban drainage and Atlantic frontage create three pathways. APA’s 2025 preliminary assessment proposes the Leça area as ARPSI PTRH2Leça01, while municipal Civil Protection distinguishes progressive, flash and urban flooding.9 10
APA’s preliminary Douro assessment proposes a combined fluvial/pluvial ARPSI on the Rio Fervença. The proposal is consultation-stage evidence and must not be represented as final detailed hazard mapping.16
The Rio Pavia and constrained urban drainage support a moderate profile in which surface-water and rapid urban flooding are more material than large-river flooding. Municipal planning includes drainage, permeability, watercourse and warning measures.11
The municipality is included in APA’s fluvial Leiria/Lis ARPSI, and the plan applies a 6% peak-flow increment to the analysed Lis 100-year scenario for 2041–2070. This does not establish that the plotted city-centre coordinate is within the floodplain.13
The urban-plan evidence documents post-heavy-rain inundation linked mainly to impermeable surfaces, concentrated runoff, changed flow paths, and blocked or undersized drainage. The profile is therefore dominated by pluvial susceptibility.14 15
Evidence points to localized exposure around small streams and drainage. Municipal planning calls for floodable-area review, peak-flow capacity assessment, retention, warning and torrential-ribeira studies.12
Long-term flood risk is not a simple function of annual rainfall. Climate change can reduce average precipitation while increasing the concentration or intensity of short-duration rainfall. Coastal sea-level rise adds a separate pathway in Porto and Matosinhos. Urbanisation can increase exposure and runoff even where river-flow projections are uncertain.
JRC PESETA IV projects rising European river-flood impacts overall. Its Portugal country-scale table shows a comparatively flat climate-only signal under a fixed present-day economy: expected annual damage is €53 million in the baseline and €57 million, €58 million and €53 million at 1.5°C, 2°C and 3°C warming, respectively.6 This national result is not a city forecast. It supports using local hydrography, official ARPSI mapping, surface-water evidence and coastal exposure rather than applying a uniform climate multiplier.
The dashboard stores the full structured evidence in data/cities.json and comparable values in data/city_scores.csv. The script build_data.py regenerates the data files from the bundled research source. The file query_apa.sh reproduces screening-envelope queries against APA’s public ArcGIS flood layers. A screening envelope is not a municipal boundary, and an intersection does not establish that the city-centre point is inundated.
The map uses OpenStreetMap data under the Open Database License and displays the required attribution.17 Standard OpenStreetMap tiles are intended for normal interactive viewing and not for bulk download or offline prefetching.18