500-year flood history in the arid environments of southeastern Spain. The case of the Almanzora River

Abstract

The study of flood events, especially analyses of flood magnitude and flood frequency, is crucial for the planning and management of settlements and infrastructure located near river channels. This work studies the historical floods of the Almanzora catchment, in southeastern Spain, one of the driest regions in Europe. We compile, describe and statistically process flood data that extend back to the year 1500 CE. The data were collected from historical sources held in both local and regional archives. The analysis of the flood record shows that the most destructive events occurred in 1550, 1729, 1879 and 1973, the last of these being the most catastrophic event on record. The synoptic configurations of the four most destructive floods in the time-series were explored and found to present the same type of pattern (cold drop). Historical flood discharges were estimated by calibrating historical flood magnitudes with instrumental data. This assessment was undertaken using a cumulative function applied to flood episodes that exceeded the threshold of magnitudes ≥3. The flood frequency analysis performed by combining instrumental and historical data shows that catastrophic events, such as the 1973 flood with a discharge of 5600 m3 s−1, occur with a return period of <100 years. We also estimate that high magnitude floods with a discharge between 684 and 3081 m3 s−1 can occur every 10-50 years. During recent decades, several municipalities and, above all, the coastal area of the Almanzora catchment have experienced significant urban growth and land use changes, as a result of the development of both tourism and extensive agriculture. This, in turn, has contributed to an increase in flood exposure.