Chronicle of a forecast flood: exposure and vulnerability on the south-east coast of Spain

In recent years, floods have become one of the natural hazards that generate the greatest economic and human losses on the planet. As is well known, torrential rainfall events are the triggering factor for flooding processes; nevertheless, it is worth examining the responsibility of the human factor, such as urban development, in the occurrence of these potential natural disasters. To this end, rainfall observations obtained during different precipitation events have been analysed. The evolution and urban development from the growth of the number of buildings was also examined. The information obtained has been crossed with the digital cartography of flooded areas (National System of Flood Zones Cartography, SNCZI in Spanish acronym). The results obtained show that the last two extraordinary rainfall events (December 2016 and September 2019) that occurred in the municipalities of Los Alcázares and San Javier (Region of Murcia, SE Spain) exceeded 200 mm, and quantified very high hourly intensities (> 50 mm/h). On the other hand, the number of buildings constructed and the built-up area in both municipalities has increased notably, with an evolution between 1950 and 2019 from 1057 to 15,969 buildings constructed, increasing from 16.09 ha. to 450.06 ha. occupied. This real estate development has caused the number of buildings exposed to flooding to reach 3840 in 2019 for a 10-year RP (return period) and 5941 for a 500-year RP. It can be concluded by indicating the clear influence of territorial transformation on the increase of exposure and economic losses generated by flood events.