Elodie BRISSET, Frédéric GUITER, Cécile MIRAMONT Tiané TROUSSIER, Yoann POHER, Rosine CARTIER Edward ANTHONY How humans feed flood: lessons from the past
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Elodie BRISSET, Frédéric GUITER, Cécile MIRAMONT Tiané TROUSSIER, Yoann POHER, Rosine CARTIER
Edward ANTHONY
How humans feed flood:
lessons from the past
Flood hasards in mountains • Steep slopes (velocity) • Highly erodible geology (sediment load)
How humans have modified past flood response to climate ?
What this means for our future ?
Future projections in the Alps (Boroneant et al., 2006)
• “Frequency of extreme precipitation is likely to increase in a warmer climate” • “More moisture will evaporate over the sea […] facilitate the built up of intense
weather systems”
Land degradation
Studying the past
Environmental reconstructions
using lake sediment archives
Long-term perspective of present/futur
changes
• Past complex environmental dynamics • Trend and threshold of long-term evolution
Case study: the alpine Lake Allos
Methods: multiproxy analysis on lake sediment archive
Chronology: 15 14C ages AMS
Sedimentology of flood layers Lamina counting on smear-slides Grain-size measurements
Palynology Chemical extraction, pollen taxa identification
Results
Increase of number of floods
Increase of low intensity flood frequency
Increase of sediment yield during high and medium
intensity floods
Increase of sediment yield
Step change 2000 years ago :
Results
Increase of number of floods
Step change 2000 years ago :
Increase of sediment yield
Transhumant pastoralism
Mining
Deforestation
Gradual change in human impact
Results
Increase of number of floods
Step change 2000 years ago :
Increase of sediment yield
Gradual change in human impact
Long term human impact induced
an abrupt and lagged response of
flood increase
Vegetation did not act its
role of buffer of
precipitations
Holocene floods over the European Alps
Flood frequency in lake sediment archives a) Allos (this study) b) Anterne (Giguet-Covex et al., 2012) c) Ledro (Vannière et al., 2013) d) Southern Alps stack (Wirth et al., 2013) e) Northern Alps stack (Wirth et al., 2013) f) Mondsee (Swierczynski et al., 2013)
Higher mean flood frequency
and higher variability
Common pattern of accelerated
erosion during the Late Holocene
By changing sensitivity of landscapes,
human societies have amplified
geomorphic response of natural hazards
contact: [email protected]
IMPLICATION FOR FUTURE • Slope sensitivity to erosion has been a
decisive long-term factor modulating flood
• Vegetation management may be crucial to significantly mitigate flood risk in the course of future more frequent climatic extremes
Schematic alpine landscape evolution
Today
2000 years ago
7000 years ago
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