Frequency and intensity of palaeofloods at the interface of Atlantic and Mediterranean climate domains

B Wilhelm,C Crouzet,F S Anselmetti,D Etienne,H Vogel

doi:10.5194/cp-12-299-2016

Abstract

Abstract. Mediterranean climatic influences was explored by studying a lake sequence (Lake Foréant) of the Western European Alps. High-resolution sedimentological and geochemical analysis revealed 171 event layers, 168 of which result from past flood events over the last millennium. The layer thickness was used as a proxy of intensity of past floods. Because the Foréant palaeoflood record is in agreement with the documented variability of historical floods resulting from local and mesoscale, summer-to-autumn convective events, it is assumed to highlight changes in flood frequency and intensity related to such events typical of both Atlantic (local events) and Mediterranean (mesoscale events) climatic influences. Comparing the Foréant record with other Atlantic-influenced and Mediterranean-influenced regional flood records highlights a common feature in all flood patterns that is a higher flood frequency during the cold period of the Little Ice Age (LIA, AD 1300–1900). In contrast, high-intensity flood events are apparent during both the cold LIA and the warm Medieval Climate Anomaly (MCA, AD 950–1250). However, there is a tendency towards higher frequencies of high-intensity flood events during the warm MCA. The MCA extremes could mean that under the global warming scenario, we might see an increase in intensity (not in frequency). However, the flood frequency and intensity in the course of the 20th century warming trend did not change significantly. Uncertainties in future evolution of flood intensity lie in the interpretation of the lack of 20th century extremes (transition or stable?) and the different climate forcing factors between the two periods (greenhouse gases vs. solar and/or volcanic eruptions).

Highlights

Heavy rainfall events trigger mountain-river floods, one of the most significant natural hazards, causing widespread loss of life, damage to infrastructure and economic deprivation (e.g. Kundzewicz et al, 2014)
The stratigraphic succession of a coarsegrained layer overlain by a graded layer suggests that the two layers were induced by a single event
Fe is the only element which elevated in event layers. These results suggest that the Fe / K ratio may be used as a millimetre-scale proxy for relative grain-size distribution and for detecting millimetre-scale event layers

Summary

Introduction

Heavy rainfall events trigger mountain-river floods, one of the most significant natural hazards, causing widespread loss of life, damage to infrastructure and economic deprivation (e.g. Kundzewicz et al, 2014). This is especially the case for the Alpine area in Europe, where tourism and recent demographic development with an increasing population raise the vulnerability of infrastructure to natural hazards One way of overcoming this issue is to extend flood series beyond observational data and compare these data sets with independent climatic and environmental forcing. In this purpose, many types of sedimentary archives have been studied (e.g. Luterbacher et al, 2012 and references therein).

Methods

Results

Discussion

Conclusion