Spain at flood risk: over a million homes stand at hazardous areas by elDiario.es

Spain at Flood Risk is an interactive and data-driven journalistic investigation that exposes the vulnerability of over a million homes in Spain to river and coastal flooding. This project, developed by elDiario.es, cross-referenced 8,000 square kilometers of flood-prone areas, as defined by the National System of Cartography of Flood Zones (SNCZI), with the footprints of more than 12 million buildings, creating the first-ever interactive map that reveals flood risks at the building level.

The findings are alarming: at least 4.3% of Spanish homes are at risk, a figure that is expected to rise due to climate change and extreme weather events. The investigation uncovers how weak regulations have allowed urbanization in high-risk areas, contributing to €7 billion in flood-related compensation over the past three decades.

For the first time, this project consolidated the cartographic records of all Spanish buildings into a unified nationwide flood risk database. Using automated geospatial processing, we analyzed each building’s exposure to flooding, considering 100-year return period flood zones. To address inconsistencies in official flood mapping across river basins, an automated standardization process was developed, redefining flood-prone areas for better accuracy.

The most innovative aspect of this project is its interactive flood risk map, which allows readers to explore street-level data on flood-prone regions. This visualization reveals entire villages within river flood perimeters and highlights new coastal developments at high risk of inundation. The data-driven storytelling format transforms abstract statistics into a tangible, immersive experience that reshapes public understanding of flood risk in Spain.

Technically, the project required significant computational effort, similar to our previous work mapping urban density in "Spain lives in flats". We developed custom scripts in R to automate the processing of 12 million buildings, integrating cadastral data, flood maps, and topographic models. We also optimized geographic data compression to ensure smooth visualization across devices, using Mapbox, D3.js, and JavaScript.

The impact of this investigation has been profound. Following the tragic floods in Valencia (October 2024), which claimed over 200 lives, thousands of people used our interactive map to assess their own risk. By making this data publicly accessible, the project empowers citizens, policymakers, and businesses to take proactive measures against future disasters.

Spain at Flood Risk is not just an investigative piece; it is a wake-up call for urban planners, policymakers, and society. Through data journalism and innovative visualization, the project highlights the urgent need for better regulations, climate adaptation, and sustainable urban planning to prevent future catastrophes.