A flood zone is territory that may be covered by water in a flood of a given return period (T10, T100, T500 years). In Spain, the SNCZI (National Flood Zone Mapping System) delineates these areas for each river basin.
Regulation
The EU Floods Directive (2007/60/EC) requires flood zone mapping and limits construction within them. However, many Spanish developments were built before these regulations in T100/T500 zones. The combination of Mediterranean torrential rain with encroachment on watercourses and dry riverbeds makes Spain one of Europe's most flood-vulnerable countries.