River response to climate variability and land-use in the Bernese Alps during the last 2400 years

Gently sloping surfaces for settlement are scarce in high mountains ranges and they are commonly related to distal parts of alluvial fans where floods hazards can be expected. To understanding the influence of external factors, such as climatic variability and land uses, on the alluvial fan accretion and flooding processes, sedimentology and pollen analysis from local site provide valuable data. Fluvial sedimentation is intermittent in time and space and sediments may be removed by subsequent reworking phases (Lewin and Macklin, 2003). Despite the discontinuities of these records, fluvial sediments provide accurate data about terrestrial environmental change such as hydrological regime, sediment supply and land use. The Alps, bordering mountains between the humid mid-latitudes with Atlantic influence and the Mediterranean subtropical zone, are especially sensitive to events of extreme precipitation and disastrous floods and to changes in the circulation of the atmosphere at global scale (Wanner et al., 2004; Pfister, 2004). Natural paleofloods result from excessive rainfall intensity and frequency, snowmelt, glaciermelt, precipitation combined with frozen soils etc. However, landuse can modify substantially mountain ecosystems and dynamics of river systems.