Interpretation of palaeohydrological changes from alluvial sequences is a complex task because of problems in the identification of their causation (climate vs. land-use change) in a region with a long history of human intervention. During the last decade there has been increasing interest in applying palaeoflood hydrology for the record of individual floods (magnitude and frequency) during the Holocene. This presentation will review the results of these analyses and evaluate changes in the spatial and temporal distribution of floods in the Spain over the last 2000 years on the bases of radiocarbon dating and environmental (documentary) history. In the Iberian Peninsula, increased flood frequency and magnitude were identified in the sedimentary record at AD 1000-1150, 1430-1700 and 1730-1800; though chronological resolution using radiocarbon dating during the last 300 years is relatively poor. The largest historical flood peak discharges since AD 1500 occurred when the North Atlantic Oscillation during the winter months was in its negative phase. In Iberian Mediterranean catchments, documentary sources indicate highest flood severity during AD 1580-1620 and AD 1840-1870. The lack of slackwater deposits between AD 1200 and 1400 highlights as a period of particularly low frequency of large floods, and is also evident in the documentary record. However, this period (1150-1450 cal. AD) comprises one of the main phases of historical floodplain aggradation of Iberian rivers that has been interpreted as a result of land-use changes. This phase of accelerated alluviation during the late medieval period is ubiquitous in Spanish rivers, and commonly resulted in the burial of irrigation structures and dams. At site-specific records (e.g. Guadalentin River), palaeoflood records indicate an anomalous increase in the frequency of large magnitude floods between AD1830-1900, which was attributed to climatic variability accentuated by intensive deforestation and land-use practices during the first decades of the 19th century. However, this late Agricultural Revolution was not synchronous all over Spain, and periods of high sediment production associated to floods may started earlier in other Mediterranean rivers (e.g. Rambla de la Viuda in Castellón).

Peer Reviewed