A climate history of droughts and floods

Dr. B. Lynn Ingram Professor, UC Berkeley Dr. Frances Malamud-Roam Senior Environmental Planner, Caltrans The questions that our book addresses:

• How much does climate vary naturally? • How frequent and severe were past droughts and floods, and how did they impact past human societies? • How will future warming impact water resources? • How can we adapt to a drier future?

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2013-2014 1976-1977

Shasta Reservoir – currently at 62% historic average for this date

Folsom Lake - currently at 76 % historic average for this date

(UPI/NASA Visible Earth)

The Dust Bowl Drought 1928-1937

(1928-1934 in ) Worst single year drought: 1976-1977

20th century floods:

1938 Orange County 1955 Santa Cruz (Santa Ana River) (San Lorenzo River)

And others: 1969, 1983, 1997, 2006… (historical reconstructions from Mock, 2006)

Sacramento Valley floodplain sediments CA Coast: Santa Barbara Basin

Megafloods occurred every 200 years

(Schimmelmann et al., 2003) El Nino / La Nina on 4 to 10 year cycles

Pacific Decadal Oscillation on 20 to 40 year cycles

Previous ice age interglacial Tree rings Lake sediments Floodplain cores

SF Bay/marsh Sediment cores Freshwater

SF Bay sediment core

• date with 14C •Separate fossil shells •Chemistry reflects salinity Drought shows up in our records during the Medieval Period, around 10th through 13th centuries Depth (cm) 0

C lay-rich 50 P eat 140 Transition to peat 305 P eat 100 1063 M ineral rich estuarine seds 1135 (B ay M ud) 150 Plant parts - rhyzomes and sheaths 1242 200 Plant roots

250 Medieval Drought

drought

wet * wet dry

(Stine, 1990) Submerged tree-stumps – Eastern Sierra Walker Lake and Lake

-A.D. 900-1100 -A.D. 1200-1350

“Medieval megadrought” Stine (Nature, 1994)

(from Swetnam et al., 2008) Mesa Verde, SW Colorado

Montezuma Castle, central Arizona

Earlier megadrought: 6000-4700 years ago

Med Drought level was much lower (trees grow along shores) Tulare Lake

Owens Lake

Humans migrated from interior deserts to the coast What about future warming? Lake Powell, 2009. Water level was down 60% from 1999 levels after a decade of drought in the West. Snowpack in will decrease in future.

More precipitation will fall as rain (instead of snow).

This will lead to larger floods in winter Warming and drying will lead to more frequent wildfires

Warming will also mean more severe storms