From flood chronologies to exposure tipping points: preliminary evidence from the Segura River Basin District, SE Spain

Flood risk in Mediterranean basins is usually discussed in relation to heavy rainfall and hydroclimatic extremes. However, the damage caused by floods is not only the result of the physical event itself. It is also shaped by the way societies have occupied flood-prone areas over time. This contribution presents preliminary results for the Segura River Basin District, in south-eastern Spain, where a long history of floods coexists with intense urbanisation, especially since the second half of the twentieth century.

The analysis is based on AMARNA, a multidisciplinary database for natural risk analysis that allows flood episodes and municipal flood cases to be reconstructed from historical, documentary, bibliographic and press sources. For the Segura basin, 664 rainfall episodes and 2,042 municipal flood cases have been identified between 1258 and 2025. Each case is classified according to hydrological behaviour, damage to infrastructure and human vulnerability. This makes it possible to compare very different historical periods and to move from a simple list of events to a more systematic interpretation of flood impacts.

In order to explore the relationship between floods and territorial exposure, the paper develops a preliminary Flood Impact and Exposure Index for the period 1900–2025. The index combines two types of information. On the one hand, it uses the AMARNA scores related to infrastructure damage and human vulnerability as an indicator of recorded impact. On the other hand, it incorporates exposure through cadastral data on the age and use of buildings, official flood-prone areas for the 10-, 100- and 500-year return periods, and population data where available. The purpose of the index is not to model hydraulic hazard, but to identify municipalities where flood impacts have become more relevant because urban growth has placed more buildings, people and activities in areas historically exposed to flooding.

The preliminary results show a complex temporal pattern. Over the full historical series, the number of recorded flood episodes increases. However, since 1900 this trend becomes less clear, while the number of affected municipalities per episode and the accumulated impact scores tend to rise, particularly after 1960. This suggests that recent flood impacts cannot be explained only by changes in rainfall. Long-standing inland hotspots such as Murcia, Orihuela, Lorca, Cartagena and Caravaca remain important, but the geography of recent impacts points to a growing concentration in coastal and peri-coastal municipalities, especially around the Mar Menor and in urbanised areas crossed by ramblas, ephemeral channels and alluvial fans.

These findings support the idea that flood risk in the Segura basin has increasingly been amplified by exposure. The expansion of tourist-residential development and other urban uses within flood-prone areas has contributed to a process of coastalisation of risk. The results also raise a broader question for adaptation policies: structural flood defence and channel modification may reduce local hazard, but they can also encourage further occupation of dangerous areas. The proposed historical-GIS approach can therefore help identify exposure tipping points and support spatial planning, disaster risk reduction and climate adaptation in Mediterranean basins.