Palaeoflood and floodplain records from Spain: Evidence for long-term climate variability and environmental changes

Abstract

Palaeoflood chronologies from seven Spanish river basins and floodplain aggradation chronologies from thirteen rivers are analysed. These fluvial records were divided in to two sub-sets, namely Atlantic (10 ka record) and Mediterranean (3 ka record) river basins, which represent distinct modern hydroclimatic conditions. In Atlantic basins floods result from intense, widespread rainfalls associated with Atlantic frontal systems transported by westerly airflow. Mediterranean river flooding is related to heavy rainfall induced by mesoscale convective systems (MCSs) during autumn months. Evidence from radiocarbon dates in slackwater flood deposits shows six periods of flood clusters at 10,750-10,240; 9550-9130; 4820-4440; 2865-2350; 960-790; and 520-290 cal BP. Despite the different flood-producing weather conditions in Atlantic and Mediterranean rivers, the radiocarbon sample clusters overlap and indicate changes in largescale atmospheric circulation and climatic conditions in the Iberian Peninsula. Comparison with proxy records of mean temperature for the Northern Hemisphere demonstrates a relationship between the period of slackwater flood deposition and cold climatic phases (e.g. the 2650 yr BP climatic event or AD 1590-1650 period of the Little Ice Age). Radiocarbon dates from aggraded floodplain sediments were clustered at 2710-2320, 2000-1830, and 910-500 cal BP. The first cluster period is in phase with the timing of slackwater deposition, whereas the third (910-500 cal BP) occurs in between two periods of increased flood frequency as indicated by the palaeoflood and documentary flood records. It is argued that the 910-500 cal BP floodplain aggradation period reflects the first post-Roman evidence of environmental change related to generalised land-use changes at the catchment scale, which produced high sediment load transported to overbank areas during high flows.

Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy

“…1500 to 1850 cal AD. This is also in agreement with the increase in flood activity during the LIA in many Mediterranean river basins (Benito et al, 2008;Moreno et al, 2008;Wilhelm et al, 2012). The comparison with Alpine summer temperature series reconstructed from tree-ring data (Büntgen et al, 2011;Corona et al, 2011) highlights a general synchronicity between summer-temperature decreases and flood-frequency increases, such that climate appears to be a significant driving factor of flood frequency variability.…”

“…100 cal BP (1850 cal AD). These periods of maximum flood frequency since 1500 cal AD have also been reported by Schmocker-Fackel and Naef (2010) from northern Switzerland, and they appear to be synchronous with multiple records of Spanish flood activity (Barriendo and Rodrigo, 2006;Benito et al, 2003), suggesting that these flood patterns result from large-scale climate changes at the European scale or larger. The long-term trend of increased flood frequency during the last millennium also contains two successive periods of low and high flood frequency, which coincide with the Medieval Warm Period (MWP) followed by the cooler Little Ice Age (LIA) from ca.…”

The Holocene occurrence of cold water corals in the NE Atlantic: Implications for coral carbonate mound evolution

“…However periods lacking corals reflect warm climate conditions in the northern Hemisphere, while those having high VMGR reflect colder climate conditions as recorded in marine and continental records (Bond et al, 2001;Vollweiler et al, 2006;Mangini et al, 2007). Moreover, periods without corals coincide with increased freshwater discharge of European rivers (Benito et al, 2008). While, glacial environmental conditions apparently inhibit reef development potentially through the absence of sufficient food or reduced bottom current activity and enhanced sedimentation, one may speculate whether particular warm periods seem to decrease coral populations as well.…”

Non-stationary flood frequency analysis in continental Spanish rivers, using climate and reservoir indices as external covariates

“…Other factors in addition to low-frequency climate variability that may influence the magnitude and frequency of river floods are linked to human activities, such as changes in land use, deforestation, dam construction, etc. With respect to continental Spain, one of the human activities that may have a considerable impact on flood frequency is the high degree of regulation of major rivers, which is the result of the construction of numerous dams in the twentieth century: the number of large dams grew from 58 in 1900 to 1195 in 2000 and with a total storage capacity of 56 500 hm 3 (Berga-Casafont, 2003), which is as high as 16 % of the annual precipitation over Spain (Estrela et al, 1999). Therefore, the effect of intensifying the strategies of regulation by dams in time must be considered when modelling floods in most of the continental Spanish rivers.…”