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A climate history of droughts and floods
Dr. B. Lynn Ingram Professor, UC Berkeley
Dr. Frances Malamud-Roam Senior Environmental Planner,
Caltrans
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The questions that our book addresses:
• How much does climate vary naturally? • How frequent and severe were past
droughts and floods and what were the impacts?
• Is our current way of life in the American West sustainable?
• How will future warming impact water resources?
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Shasta Reservoir
Folsom Lake
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(UPI/NASA Visible Earth)
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The Dust Bowl Drought 1928-1937 (1928-1934 in California)
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Worst single year drought: 1976-1977
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Looking at the past using environmental proxies
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Provide a history of fires
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Other proxy records
Ring widths Air bubbles Temperature Sea level
Ice cores
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SEDIMENT CORES
Oceans; lakes; estuaries; bogs; marshes
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Tree rings Lake sediments Floodplain cores San Francisco Bay Sediments – why are they so informative?
California climate archives
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date with 14C Separate fossil
shells Chemistry
reflects salinity
San Francisco Bay sediment core
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Unusual period of drying
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1977 Scirpus
1995 - after 5 yr drought Spartina
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Depth(cm)
Plant roots
Plant parts -rhyzomesand sheaths
140
1063
1242
1135
305
0
50
100
150
200
250
Trans itionto pea tP eat
C lay-richP eat
M inera l richestuarine seds(B ay M ud)
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What do other records tell us about this time?
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(Stine, 1990)
wet dry *
drought
wet
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Submerged tree-stumps -A.D. 900-1100 -A.D. 1200-1350
Stine (Nature, 1994)
“Medieval megadrought”
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(from Swetnam et al., 2008)
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Mesa Verde, SW Colorado
Montezuma Castle, central Arizona
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Other climate swings
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Earlier megadrought 6000-4700 years ago
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Lake Tahoe level was much lower (trees grow along shores)
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Owens Lake
Tulare Lake
Humans migrated from interior deserts to the coast
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1938 Orange County (Santa Ana River)
20th century floods:
1955 Santa Cruz (San Lorenzo River)
And others: 1969, 1983, 1997, 2006…
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(historical reconstructions from Mock, 2006)
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CA Coast: Santa Barbara Basin
Sacramento Valley floodplain sediments
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Megafloods occurred every 200 years
(Schimmelmann et al., 2003)
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What about future warming?
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Lake Powell, 2009. Water level was down 60% from 1999 levels after a decade of drought in the West.
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Warming and drying will lead to more frequent wildfires
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Snowpack in Sierra Nevada will decrease in future. More precipitation will fall as rain (instead of snow). This will lead to larger floods in winter